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. 2021 Feb 26;16(2):e0247926. doi: 10.1371/journal.pone.0247926

Protein intake in inhabitants with regular exercise is associated with sleep quality: Results of the Shika study

Fumihiko Suzuki 1,*, Emi Morita 2,3, Sakae Miyagi 4, Hiromasa Tsujiguchi 1,5, Akinori Hara 1,5, Thao Thi Thu Nguyen 1,6, Yukari Shimizu 1,7, Koichiro Hayashi 1,8, Keita Suzuki 1,8, Takayuki Kannon 5,9, Atsushi Tajima 5,9, Sumire Matsumoto 2,10, Asuka Ishihara 2,10, Daisuke Hori 11, Shotaro Doki 11, Yuichi Oi 11, Shinichiro Sasahara 11, Makoto Satoh 2, Ichiyo Matsuzaki 2,11, Masashi Yanagisawa 2, Toshiharu Ikaga 12, Hiroyuki Nakamura 1,5
Editor: Jose M Moran13
PMCID: PMC7909647  PMID: 33635905

Abstract

Study objectives

Although associations between sleep quality and environmental factors and nutrient intake have been reported, interactions between these factors have not been elucidated in detail. Therefore, this cross-sectional study examined the effects of regular exercise and nutrient intake on sleep quality using the Pittsburgh Sleep Quality Index (PSQI), which is the most frequently used index for sleep evaluation.

Methods

The participants included 378 individuals aged 40 years or older living in Shika Town, Ishikawa Prefecture. Of these individuals, 185 met the inclusion criteria. The participants completed a self-administered questionnaire assessing lifestyle habits and frequency and duration of exercise, the PSQI, and the brief-type self-administered diet history questionnaire (BDHQ) on nutrient intake.

Results

A two-way analysis of covariance on regular exercise and PSQI scores indicated that protein intake (17.13% of energy) was significantly higher in the regular exercise and PSQI ≤10 groups than in the non-regular exercise or PSQI ≥11 groups (p = 0.002). In a multiple logistic regression analysis with PSQI scores (≤10 and ≥11), protein intake was a significant independent variable in any of the models adjusted for confounding factors such as age, sex, body mass index, current smoker, and current drinker (OR: 1.357, 95% CI: 1.081, 1.704, p = 0.009) in the regular exercise group but not in the non-regular exercise group.Conclusions

We identified a positive relationship between sleep quality and protein intake in the regular exercise group. These findings suggest that regular exercise at least twice a week for 30 minutes or longer combined with high protein intake contributes to good sleep quality.

Introduction

Sleep plays an important role in maintaining health. Sleep disorders have been shown to negatively affect lifestyle-related diseases, such as metabolic syndrome [1], hypertension [2, 3], diabetes [4, 5], and cardiovascular disease [6, 7]. The following underlying mechanisms have been suggested for this association: neurobiological and physiological stressors [2]; the inhibition of glycemic control, which increases dietary intake through the secretion of ghrelin [5]; and the promotion of insulin resistance by increasing cortisol, IL-6, and TNFα levels [5]. Therefore, preventing sleep disorders is important for maintaining health.

Exercise has been noted to have a positive impact on sleep disorders. Epidemiological studies on sleep disorders and exercise/physical activity have examined non-restorative sleep in middle-aged and elderly individuals [8] and sleep quality in nursing homes [9]. Intervention studies have reported improvements in sleep quality in adults [10] and elderly individuals with depression [11]. Exercise affects sleep via the following mechanisms: its thermoregulatory effects reduce wake times during the night [10], it facilitates sleep onset by activating a heat dissipation mechanism controlled by the hypothalamus to increase central body temperature [12], and it improves mood due to its antidepressant/anxiety effects [13]. In animal studies, exercise was shown to increase the levels of adenosine, which activates the sleep center in the hypothalamus [14], and serotonin, which synthesizes the sleep hormone melatonin [12].

Nutrition has been investigated as another factor related to sleep disorders. Epidemiological studies have reported a relationship between sleep quality and micronutrients such as carotenoids [15], vitamin B12 [15, 16], calcium [17], and selenium [18]. However, the relationships between sleep and macronutrients remain unclear. A previous study indicated the presence of a relationship between sleep and protein intake [16], but another study reported that no such relationship existed [19]. The latter study demonstrated that sleep was associated with lipid and carbohydrate intake [19]. Thus, the findings obtained from previous epidemiological studies are inconsistent. These discrepancies may exist because of the lack of a uniform method for evaluations using questionnaires [15, 16, 18, 20, 21]. Therefore, we conducted an epidemiological study to investigate the factors affecting sleep using the Pittsburgh Sleep Quality Index (PSQI), which is one of the most frequently used indices for evaluating self-rated sleep quality in sleep medicine.

The role of environmental factors must be considering when examining the association between nutrient intake and sleep. However, previous studies have not yet investigated this triangular relationship in detail. Two previous studies that reported different findings on the relationship between protein intake and sleep [16, 19] did not perform an analysis adjusted for environmental factors such as exercise. Therefore, the effects of interactions between environmental factors and nutrient intake on sleep remain unclear. The present cross-sectional study examined the effects of regular exercise and nutrient intake on sleep quality.

Methods

Data collection

In this cross-sectional study, comprehensive health survey data were collected from the residents of Shika Town, Ishikawa Prefecture, Japan, between November 2017 and February 2018. As of November 2017, there were 21,007 residents in Shika Town, and 15,012 were older than 40 years [22]. The Shika study epidemiologically investigates the causes of lifestyle-related diseases through interviews, self-administered questionnaires, and comprehensive medical examinations. Previous studies have also examined the relationship between nutrition and health [23–25].

Participants

This study was conducted on participants recruited from those who underwent a medical examination in Shika Town. For details, a total of 378 people aged 40 years and older who live in four model districts (Horimatsu, Tsuchida, Higashimatsudo, and Togi) provided their consent to participate in this sleep study. Of these individuals, 193 were excluded because they did not meet the survey criteria [169 participants did not complete the brief-type self-administered diet history questionnaire (BDHQ), 1 participant did not have energy records within 600 – 4000Kcal/day, and 23 participants did not complete the smoking, drinking, or exercise questionnaire]. Fig 1 shows the inclusion criteria. In total, 185 participants (95 males and 90 females; mean age ± standard deviation: 60.5 ± 9.7 years, range 41–83 years) who answered all relevant questions in the questionnaires and did not withdraw their consent were included in the analysis.

Fig 1. Participant recruitment chart.

Fig 1

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* This reference value was chosen for the following reasons: less than 600 kcal/day is equivalent to half the energy intake required for the lowest physical activity category; more than 4000 kcal/day is equivalent to 1.5 times the energy intake required for the medium physical activity category.

Questionnaire and measurements

The participants completed a self-administered questionnaire on lifestyle and underlying diseases. Lifestyle items included the number of exercise days per week and the mean exercise time during each session, whether they were current smokers (1. yes, 2. no) and/or current drinkers (1. yes, 2. no), and education (1. junior high school, 2. high school 3. junior college, 4. university or higher). Underlying disease items included metabolic syndrome (1. yes, 2. no), hypertension (1. yes, 2. no), diabetes (1. yes, 2. no), angina (1. yes, 2. no), myocardial infarction (1. yes, 2. no), and depression (1. yes, 2. no). Body mass index (BMI) was measured using health survey data from the Shika study.

Nutrient intake was assessed using the BDHQ [26, 27]. The BDHQ is a four-page structured questionnaire that assesses the consumption frequency of 58 foods and beverages that are commonly consumed by the general Japanese population. The BDHQ estimates dietary intake in the last month using an ad hoc computer algorithm. The validity of the BDHQ has been demonstrated in previous studies in Japanese populations [26, 27]. To analyze nutrient data, the density method was used to estimate intake per 1000 Kcal. The following formula was used to calculate the energy intake ratio (% energy) of energy-producing nutrients (proteins, lipids, carbohydrates, and alcohol): energy intake from each nutrient/energy intake (EN) × 100, adjusted intake of non-energy-producing nutrients: crude intake of various nutrients/EN × 1000 Kcal.

Sleep status was assessed using the PSQI [28, 29]. The PSQI assesses sleep quality and disturbances over a one-month period and consists of the following components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbance, the use of sleeping medication, and daytime dysfunction. Each component of the PSQI is scored from 0 to 3. The PSQI global score is a sum of these components that ranges between 0 and 21, with higher scores indicating poorer sleep quality. The validity of the PSQI has been demonstrated in previous studies in Japanese populations [29].

Statistical analysis

Regular exercise was defined as exercise for at least 30 minutes at a time and twice a week [30]. Buysse et al. [28] defined a PSQI score >5 as poor sleep quality; however, their study population included adolescents and differed from that in our Shika study, which included those aged 40 years and older. In the present study, the median PSQI of the participants was 10; thus, they were classified into PSQI ≤10 and ≥11 groups. The age distribution of the participants in the present study did not differ from that of the Shika Town inhabitants.

The distribution of variables was checked by the Kolmogorov–Smirnov, and Shapiro–Wilk normality tests, or the normal distribution curve in the histogram was confirmed before using other statistical tests. The Student’s t-test was used to compare the means of continuous variables and the Chi-square test was performed to compare the proportions of categorical variables. All participants were stratified into two groups based on their PSQI scores (PSQI ≤10 and ≥11) and whether they participated in regular exercise (regular exercise group and non-regular exercise group). A two-way analysis of covariance (ANCOVA) was used to examine the effects of the interaction between regular exercise and PSQI on nutrient intake. The following confounding factors were adjusted for: age, sex, BMI, current smoker, current drinker, education, hypertension, and diabetes. A multiple logistic regression analysis was conducted to examine the effects of regular exercise and nutrient intake on sleep quality. The dependent variable was the PSQI (≤10 and ≥11). We used three models in the logistic regression analysis. Model 1 included the individual factors of age, gender, and BMI. Model 2 included the environmental factors of current smoker and current drinker together with individual factors. Model 3 included the disease factors of hypertension and diabetes together with individual factors. Additionally, the analyses were stratified by whether the participants performed regular exercise. Pearson’s correlation coefficient was used to confirm multicollinearity. Specifically, there was no value of | r | >0.9 in the correlation matrix table between independent variables. The forced input method was used for variable selection. The significance level was set at 5%. IBM SPSS Statistics version 25 for Windows (IBM, Armonk, NY, USA) was used for the statistical analysis.

Ethics statement

The present study was conducted with the approval of the Ethics Committee of Kanazawa University (No. 1491). Written informed consent was obtained from all participants.

Results

Participant characteristics

The participants’ sleep quality and nutrient intakes are shown in Table 1. Among the 185 participants, there were 95 males with a mean age of 60.9 years (SD = 9.6) and 90 females with a mean age of 60.3 years (SD = 10.1); there was no significant difference between genders. BMI (p < 0.001) was significantly higher in males than in females. Significantly more males were current smokers (p < 0.000), current drinkers (p < 0.001), and had metabolic syndrome (p < 0.001), diabetes (p = 0.049), and angina (p = 0.019) than females. The mean PSQI was 10.7 (SD = 2.7) in males and 10.7 (SD = 2.8) in females, with no significant difference between genders. When comparing nutrients, the total energy (p < 0.001) was significantly higher in males. Conversely, the intakes of other nutrients, excluding carbohydrates, sodium, vitamin D, and vitamin B12, were significantly higher in females.

Table 1. Participant characteristics.

  Total (N = 185) Male (N = 95) Female (N = 90) p Value *
  Mean (n) SD (%) Mean (n) SD (%) Mean (n) SD (%)
Age, years 60.5 9.7 60.9 9.6 60.3 10.1 0.791
BMI, kg/m2 23.1 3.1 23.8 3.3 22.2 2.6 <0.001
Exercise / week, days 1.5 2.3 1.4 2.4 1.5 2.2 0.700
Exercise time / each session, minutes 27.2 52.2 24.4 53.4 30.2 51.0 0.452
Current smoker, n (%) 31 16.8 25 26.3 6 6.7 <0.001
Current drinker, n (%) 107 57.8 75 78.9 32 35.6 <0.001
Education 0.142
    Junior high school, n (%) 38 20.5 19 20.0 19 21.1
    High school, n (%) 79 42.7 39 41.1 40 44.4
    Junior college, n (%) 39 21.1 15 15.8 24 26.7
    University or higher, n (%) 29 15.7 22 23.2 7 7.8
PSQI 10.7 2.7 10.7 2.7 10.7 2.8 0.988
Underlying diseases              
metabolic syndrome, n (%) 46 24.9 36 37.9 10 11.1 <0.001
Hypertension, n (%) 61 32.8 37 38.5 24 26.5 0.086
Diabetes, n (%) 14 8.0 11 12.1 3 3.6 0.049
Angina, n (%) 10 5.4 9 9.9 1 1.2 0.019
Myocardial infarction, n (%) 3 1.6 2 2.2 1 1.2 1.000
Depression, n (%) 1 0.6 1 1.1 0 0.0 1.000
Nutrients              
Total energy, Kcal 1968.21 632.39 2214.45 648.63 1708.29 499.40 <0.001
Protein, %energy 15.11 3.08 14.33 3.12 15.93 2.84 <0.001
Fat, % energy 25.36 5.76 23.65 5.91 27.17 5.04 <0.001
Carbohydrate, % energy 53.66 7.58 53.08 7.97 54.27 7.15 0.287
minerals, % energy 10.32 1.98 9.72 1.89 10.94 1.88 <0.001
Sodium, mg/1000 Kcal 2397.76 486.77 2338.00 493.78 2460.84 473.82 0.086
Potassium, mg/1000 Kcal 1413.49 412.08 1252.45 331.72 1583.49 421.83 <0.001
Calcium, mg/1000 Kcal 291.66 109.87 260.60 109.61 324.45 100.74 <0.001
Magnesium, mg/1000 Kcal 141.30 32.01 130.51 28.43 152.68 31.76 <0.001
Phosphorus, mg/1000 Kcal 573.06 129.32 537.85 132.97 610.22 114.81 <0.001
Iron, mg/1000 Kcal 4.23 1.05 3.86 0.88 4.61 1.08 <0.001
Zinc, mg/1000 Kcal 4.47 0.64 4.28 0.68 4.67 0.53 <0.001
β-carotene equivalent, μg/1000 Kcal 2044.46 1278.57 1630.35 975.87 2481.58 1413.37 <0.001
Retinol equivalent, μg/1000 Kcal 359.43 175.78 325.33 177.92 395.43 167.03 0.006
Vitamin D, μg/1000 Kcal 8.17 5.23 7.83 5.33 8.53 5.12 0.363
α-Tocopherol, mg/1000 Kcal 3.96 1.06 3.58 0.91 4.37 1.07 <0.001
Vitamin K, μg/1000 Kcal 168.40 87.03 142.38 67.30 195.85 96.90 <0.001
Vitamin B1, mg/1000 Kcal 0.41 0.09 0.38 0.08 0.45 0.09 <0.001
Vitamin B2, mg/1000 Kcal 0.66 0.17 0.61 0.16 0.72 0.16 <0.001
Niacin, mg/1000 Kcal 9.47 2.49 8.90 2.36 10.08 2.49 0.001
Vitamin B6, mg/1000 Kcal 0.70 0.17 0.65 0.15 0.75 0.18 <0.001
Vitamin B12, μg/1000 Kcal 5.53 2.75 5.31 2.77 5.77 2.72 0.258
Folic acid, μg/1000 Kcal 178.61 63.21 158.26 50.75 200.09 68.06 <0.001
Pantothenic acid, mg/1000 Kcal 3.40 0.72 3.13 0.66 3.69 0.67 <0.001
Vitamin C, mg/1000 Kcal 63.04 31.90 53.24 25.05 73.39 35.07 <0.001
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* p-values were calculated from the Student’s t-tests for continuous variables and from the Chi-square test for categorical variables (p-values less than 0.05 are highlighted in bold). Abbreviations: SD, standard deviation; BMI, body mass index; PSQI, Pittsburgh Sleep Quality Index.

Comparison with the PSQI

The mean age of the 106 participants in the PSQI ≤10 group was 59.2 years, which was significantly younger than that of the 79 participants in the PSQI ≥11group (62.4 years, p = 0.026) (Table 2). The PSQI ≤10 group reported significantly more exercise days per week (p = 0.004) and a significantly longer mean exercise time per session (p = 0.008). Furthermore, these factors were significantly greater in the PSQI ≤10 group even after adjusting for age, sex, BMI, current smoker, current drinker, education, hypertension, and diabetes (exercise days and exercise time: p < 0.001 and p = 0.004, respectively). Therefore, regular exercise was beneficial for sleep quality. The proportion of participants with metabolic syndrome (p = 0.026) was significantly higher in the PSQI ≤10 group. When comparing each nutrient, the intakes of retinol equivalent (p = 0.044) and vitamin B2 (p = 0.024) were significantly higher in the PSQI ≤10 group than in the PSQI ≥11 group.

Table 2. Differences in characteristics and daily nutrient intake between the PSQI ≤10 and ≥11 groups.

  Total (N = 185)
PSQI ≤ 10 (n = 106) PSQI ≥ 11 (n = 79) p Value *
  Mean (n) SD (%) Mean (n) SD (%)
Age, years 59.2 9.9 62.4 9.3 0.026
Sex: male, n (%) 50 47.2 45 57.0 0.234
BMI, kg/m2 23.4 3.1 22.6 3.0 0.064
Exercise / week, days 1.9 2.5 1.0 1.8 0.004
Exercise time / each session, minutes 35.3 61.9 16.3 32.5 0.008
Current smoker, n (%) 19 17.9 12 15.2 0.693
Current drinker, n (%) 58 54.7 49 62.0 0.367
Education 0.427
    Junior high school, n (%) 18 17.0 20 25.3
    High school, n (%) 48 45.3 31 39.2
    Junior college, n (%) 23 21.7 16 20.3
    University or higher, n (%) 17 16.0 12 15.2
PSQI 8.9 1.2 13.2 2.2 <0.001
Underlying diseases          
metabolic syndrome, n (%) 33 31.1 13 16.5 0.026
Hypertension, n (%) 33 31.1 28 35.6 0.636
Diabetes, n (%) 6 5.9 8 10.1 0.275
Angina, n (%) 5 5.0 5 6.8 0.746
Myocardial infarction, n (%) 2 2.0 1 1.4 1.000
Depression, n (%) 0 0.0 1 1.4 0.427
Nutrients          
Total energy, Kcal 1993.88 673.94 1933.77 574.35 0.524
Protein, %energy 15.48 3.07 14.61 3.05 0.056
Fat, % energy 25.80 5.54 24.77 6.04 0.229
Carbohydrate, % energy 53.58 7.35 53.76 7.94 0.873
minerals, % energy 10.46 1.95 10.13 2.01 0.270
Sodium, mg/1000 Kcal 2407.42 471.59 2384.80 509.17 0.755
Potassium, mg/1000 Kcal 1449.58 418.96 1365.07 400.18 0.168
Calcium, mg/1000 Kcal 300.81 115.94 279.39 100.56 0.190
Magnesium, mg/1000 Kcal 143.67 32.37 138.12 31.44 0.244
Phosphorus, mg/1000 Kcal 587.05 133.72 554.28 121.50 0.088
Iron, mg/1000 Kcal 4.34 1.06 4.08 1.02 0.097
Zinc, mg/1000 Kcal 4.55 0.61 4.37 0.66 0.058
β-carotene equivalent, μg/1000 Kcal 2151.41 1347.64 1900.95 1172.67 0.179
Retinol equivalent, μg/1000 Kcal 381.22 189.21 330.20 152.28 0.044
Vitamin D, μg/1000 Kcal 8.56 5.74 7.65 4.43 0.226
α-Tocopherol, mg/1000 Kcal 4.02 1.05 3.89 1.07 0.398
Vitamin K, μg/1000 Kcal 175.54 93.46 158.81 77.11 0.185
Vitamin B1, mg/1000 Kcal 0.42 0.09 0.40 0.10 0.183
Vitamin B2, mg/1000 Kcal 0.69 0.18 0.63 0.16 0.024
Niacin, mg/1000 Kcal 9.77 2.37 9.06 2.61 0.054
Vitamin B6, mg/1000 Kcal 0.70 0.18 0.69 0.17 0.541
Vitamin B12, μg/1000 Kcal 5.72 2.83 5.28 2.63 0.290
Folic acid, μg/1000 Kcal 181.94 65.37 174.14 60.32 0.408
Pantothenic acid, mg/1000 Kcal 3.49 0.74 3.29 0.67 0.058
Vitamin C, mg/1000 Kcal 62.66 31.54 63.56 32.57 0.850
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* p-values were calculated from the Student’s t-tests for continuous variables and from the Chi-square test for categorical variables (p-values less than 0.05 are highlighted in bold). Abbreviations: PSQI, Pittsburgh Sleep Quality Index; SD, standard deviation; BMI, body mass index.

Comparisons with regular exercise

The mean age of the 59 participants in the regular exercise group (64.2 years) was significantly older than that of the 126 participants in the non-regular exercise group (58.8 years, p < 0.001) (Table 3). The mean PSQI (p = 0.003) was significantly higher in the non-regular exercise group. When comparing each nutrient, the intakes of protein (p <0.001), minerals (p < 0.001), and 12 kinds of vitamins were significantly higher in the regular exercise group than that in the non-regular exercise group.

Table 3. Differences in characteristics and daily nutrient intake between regular and non-regular exercise groups.

  Total (N = 185)        
Regular exercise (n = 59)   Non-regular exercise (n = 126)   p Value *
  Mean (n) SD (%) Mean (n) SD (%)  
Age, years 64.2 7.8 58.8 10.1 <0.001
Sex: male, n (%) 26 44.1 69 54.8 0.208
BMI, kg/m2 22.8 3.0 23.2 3.1 0.378
Exercise / week, days 4.3 1.7 0.2 0.8 <0.001
Exercise time / each session, minutes 80.3 64.2 2.3 11.7 <0.001
Current smoker, n (%) 5 8.5 26 20.6 0.056
Current drinker, n (%) 30 50.8 77 61.1 0.204
Education 0.536
    Junior high school, n (%) 13 22.0 25 19.8
    High school, n (%) 27 45.8 52 41.3
    Junior college, n (%) 10 16.9 29 23.0
    University or higher, n (%) 9 15.3 20 15.9
PSQI 9.9 2.2 11.1 2.9 0.003
Underlying diseases      
metabolic syndrome, n (%) 15 25.4 31 24.6 1.000
Hypertension, n (%) 21 35.6 40 31.7 0.618
Diabetes, n (%) 7 11.9 7 5.6 0.144
Angina, n (%) 2 3.4 8 6.3 0.506
Myocardial infarction, n (%) 1 1.7 2 1.6 1.000
Depression, n (%) 0 0.0 1 0.8 1.000
Nutrients        
Total energy, Kcal 1961.70 554.63 1971.26 667.77 0.924
Protein, %energy 16.33 3.42 14.54 2.74 <0.001
Fat, % energy 25.79 6.04 25.16 5.64 0.488
Carbohydrate, % energy 52.63 6.80 54.14 7.90 0.206
minerals, % energy 11.10 1.99 9.95 1.87 <0.001
Sodium, mg/1000 Kcal 2460.96 473.81 2368.17 491.78 0.228
Potassium, mg/1000 Kcal 1624.20 432.14 1314.83 364.07 <0.001
Calcium, mg/1000 Kcal 349.42 124.82 264.62 90.70 <0.001
Magnesium, mg/1000 Kcal 156.34 32.86 134.25 29.15 <0.001
Phosphorus, mg/1000 Kcal 635.65 146.91 543.75 109.04 <0.001
Iron, mg/1000 Kcal 4.71 1.10 4.00 0.95 <0.001
Zinc, mg/1000 Kcal 4.72 0.72 4.36 0.57 <0.001
β-carotene equivalent, µg/1000 Kcal 2629.14 1537.63 1770.68 1035.57 <0.001
Retinol equivalent, µg/1000 Kcal 436.79 206.07 323.21 147.08 <0.001
Vitamin D, µg/1000 Kcal 9.95 6.46 7.34 4.32 0.001
α-Tocopherol, mg/1000 Kcal 4.34 1.16 3.79 0.97 0.001
Vitamin K, µg/1000 Kcal 199.24 92.18 153.95 80.91 0.001
Vitamin B1, mg/1000 Kcal 0.46 0.10 0.39 0.08 <0.001
Vitamin B2, mg/1000 Kcal 0.75 0.16 0.63 0.16 <0.001
Niacin, mg/1000 Kcal 10.21 2.54 9.12 2.40 0.005
Vitamin B6, mg/1000 Kcal 0.77 0.17 0.66 0.16 <0.001
Vitamin B12, µg/1000 Kcal 6.18 2.92 5.23 2.62 0.027
Folic acid, µg/1000 Kcal 207.76 66.76 164.96 56.79 <0.001
Pantothenic acid, mg/1000 Kcal 3.74 0.73 3.25 0.66 <0.001
Vitamin C, mg/1000 Kcal 76.62 34.64 56.68 28.52 <0.001
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* p-values were calculated from the Student’s t-tests for continuous variables and from the Chi-square test for categorical variables (p-values less than 0.05 are highlighted in bold). Abbreviations: PSQI, Pittsburgh Sleep Quality Index; SD, standard deviation; BMI, body mass index.

Effects of the interaction between regular exercise and the PSQI on nutrient intake

The regular exercise group was divided into two groups based on PSQI scores; there were 43 participants in the PSQI ≤10 group and 16 in the PSQI ≥11 group. The non-regular exercise group was similarly divided into two groups based on the PSQI scores; there were 63 participants in the PSQI ≤10 group and 63 in the PSQI ≥11 group (Table 4). A two-way ANCOVA adjusting for age, sex, BMI, current smoker, current drinker, education, hypertension, and diabetes was used to examine the effects of interactions between regular exercise and the PSQI on nutrient intake. Interactions were observed for age (p = 0.006), education (p = 0.002), protein (p = 0.002), carbohydrate (p = 0.045), phosphorus (p = 0.008), zinc (p = 0.031), vitamin D (p = 0.015), vitamin B12 (p = 0.007), and pantothenic acid (p = 0.008). A post hoc Bonferroni analysis indicated that there was significantly higher protein intake in the PSQI ≤10 group than in the PSQI ≥11 group with regular exercise (p = 0.001); however, there was no difference between the two PSQI groups without regular exercise (S1 Fig).

Table 4. Interactions between exercise groups and PSQI groups.

  Total (N = 185)
Regular exercise (n = 59) Non-regular exercise (n = 126) p Value *
PSQI ≤ 10 (n = 43) PSQI ≥ 11 (n = 16) PSQI ≤ 10 (n = 63) PSQI ≥ 11 (n = 63) RE PSQI RE * PSQI
Mean 95% CI Mean 95% CI Mean 95% CI Mean 95% CI
  Lower Upper Lower Upper Lower Upper Lower Upper
Age, years 64.2 61.9 66.6 64.2 59.8 68.6 55.7 53.3 58.2 61.9 59.5 64.3 0.003 0.180 0.006
Sex † 1.4 1.2 1.6 1.6 1.3 1.8 1.5 1.4 1.7 1.6 1.5 1.7 0.532 0.276 0.469
BMI, kg/m2 23.0 22.1 23.8 22.2 20.1 24.2 23.7 22.9 24.6 22.7 22.0 23.4 0.217 0.037 0.721
Current smoker ‡ 1.9 1.8 2.0 1.9 1.8 2.1 1.8 1.7 1.9 1.8 1.7 1.9 0.111 0.2 0.702
Current drinker ‡ 1.5 1.4 1.7 1.4 1.1 1.6 1.4 1.3 1.5 1.4 1.3 1.5 0.525 0.279 0.751
Education § 2.4 2.1 2.7 1.9 1.4 2.4 2.4 2.1 2.6 2.4 2.1 2.6 0.712 0.414 0.002
Underlying diseases                              
Metabolic syndrome, % 1.7 1.6 1.86 1.81 1.6 2.0 1.7 1.6 1.8 1.8 1.8 1.9 0.565 0.133 0.922
Hypertension, % 1.6 1.5 1.78 1.69 1.4 1.9 1.7 1.6 1.8 1.6 1.5 1.8 0.566 0.601 0.332
Diabetes, % 1.9 1.9 2.01 1.75 1.5 2.0 2.0 1.9 2.0 1.9 1.9 2.0 0.013 0.023 0.064
Angina, % 2.0 1.9 2.02 1.94 1.8 2.1 1.9 1.9 2.0 1.9 1.9 2.0 0.429 0.89 0.334
Myocardial infarction, % 2.0 1.9 2.02 2.00 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 0.488 0.375 0.441
Depression, % 2.0 2.0 2.0 2.00 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 0.263 0.964 0.263
Nutrients                              
Total energy, Kcal 2012.22 1850.69 2173.76 1825.92 1492.71 2159.12 1981.37 1789.21 2173.52 1961.16 1819.44 2102.88 0.369 0.043 0.348
Protein, %energy 17.13 16.11 18.14 14.19 12.65 15.73 14.36 13.77 14.95 14.71 13.93 15.49 0.321 0.005 0.002
Fat, % energy 26.67 24.77 28.57 23.45 20.71 26.20 25.22 23.95 26.48 25.11 23.54 26.68 0.817 0.358 0.218
Carbohydrate, % energy 51.59 49.34 53.84 55.42 53.16 57.67 54.94 53.15 56.73 53.34 51.17 55.51 0.610 0.317 0.045
minerals, % energy 11.42 10.84 11.99 10.24 9.10 11.38 9.80 9.36 10.24 10.10 9.60 10.61 0.112 0.197 0.108
Sodium, mg/1000 Kcal 2523.05 2384.08 2662.02 2294.09 2024.30 2563.89 2328.50 2209.59 2447.41 2407.83 2279.05 2536.62 0.926 0.334 0.102
Potassium, mg/1000 Kcal 1671.49 1550.93 1792.05 1497.12 1220.88 1773.37 1298.12 1205.30 1390.94 1331.53 1240.45 1422.62 0.002 0.478 0.591
Calcium, mg/1000 Kcal 368.18 329.05 407.30 298.99 242.42 355.56 254.83 234.49 275.17 274.41 249.38 299.43 0.019 0.068 0.096
Magnesium, mg/1000 Kcal 161.14 151.71 170.57 143.46 124.24 162.68 131.74 124.70 138.78 136.76 129.12 144.40 0.028 0.206 0.150
Phosphorus, mg/1000 Kcal 665.26 620.65 709.87 556.08 490.07 622.09 533.67 509.90 557.44 553.83 523.13 584.53 0.058 0.018 0.008
Iron, mg/1000 Kcal 4.90 4.58 5.23 4.18 3.61 4.75 3.95 3.73 4.17 4.05 3.80 4.31 0.088 0.032 0.105
Zinc, mg/1000 Kcal 4.85 4.65 5.06 4.35 3.94 4.76 4.34 4.22 4.46 4.37 4.21 4.53 0.235 0.021 0.031
β-carotene equivalent, μg/1000 Kcal 2739.29 2267.63 3210.94 2333.12 1501.24 3165.01 1750.17 1488.28 2012.05 1791.19 1529.47 2052.91 0.014 0.353 0.949
Retinol equivalent, μg/1000 Kcal 466.74 398.27 535.20 356.31 288.61 424.01 322.85 288.53 357.17 323.57 283.71 363.43 0.028 0.047 0.208
Vitamin D, μg/1000 Kcal 10.97 8.85 13.10 7.19 5.00 9.38 6.92 5.89 7.95 7.77 6.63 8.91 0.414 0.029 0.015
α-Tocopherol, mg/1000 Kcal 4.51 4.16 4.85 3.87 3.25 4.49 3.69 3.47 3.91 3.89 3.63 4.16 0.181 0.402 0.13
Vitamin K, μg/1000 Kcal 214.78 185.43 244.14 157.46 120.42 194.50 148.75 127.93 169.57 159.16 139.15 179.16 0.33 0.058 0.072
Vitamin B1, mg/1000 Kcal 0.47 0.44 0.50 0.42 0.36 0.49 0.39 0.37 0.41 0.40 0.38 0.42 0.012 0.387 0.302
Vitamin B2, mg/1000 Kcal 0.78 0.73 0.83 0.65 0.58 0.72 0.62 0.58 0.67 0.63 0.59 0.67 0.031 0.021 0.094
Niacin, mg/1000 Kcal 10.60 9.84 11.35 9.17 7.82 10.52 9.21 8.67 9.75 9.03 8.37 9.70 0.146 0.14 0.179
Vitamin B6, mg/1000 Kcal 0.80 0.75 0.85 0.71 0.62 0.80 0.64 0.60 0.68 0.68 0.64 0.72 0.025 0.501 0.109
Vitamin B12, μg/1000 Kcal 6.79 5.85 7.72 4.57 3.61 5.52 4.99 4.37 5.60 5.46 4.76 6.17 0.965 0.034 0.007
Folic acid, μg/1000 Kcal 214.72 194.79 234.65 189.06 151.45 226.67 159.57 145.45 173.69 170.35 155.88 184.82 0.02 0.425 0.449
Pantothenic acid, mg/1000 Kcal 3.91 3.70 4.12 3.28 2.94 3.62 3.20 3.04 3.36 3.29 3.12 3.46 0.046 0.026 0.008
Vitamin C, mg/1000 Kcal 76.90 67.10 86.70 75.86 53.24 98.47 52.93 45.99 59.88 60.43 53.09 67.78 0.008 0.382 0.731
Open in a new tab

* Analysis of covariance (p-values less than 0.05 are highlighted in bold). Adjusted for age, sex, BMI, current smoker, current drinker, education, hypertension, and diabetes.

† sex (1. female, 2. male)

‡ current smoker or drinker (1. yes, 2. no)

§ education (1. junior high school, 2. high school, 3. junior college, 4. university and higher)

¶ underlying diseases (1. yes, 2. no). Abbreviations: PSQI, Pittsburgh Sleep Quality Index; RE, regular exercise; CI, confidence interval; BMI, body mass index.

Effects of regular exercise and protein intake on sleep quality

Table 5 shows the results of a multiple logistic regression analysis with PSQI (≤ 10 and ≥11) stratified by regular exercise. Protein intake was a significant independent variable in any models that were adjusted for individual factors (age, sex, and BMI; OR: 1.260; 95% CI: 1.037, 1.531; p = 0.020), individual and environmental factors (current smoker and current drinker; OR: 1.357; 95% CI: 1.081, 1.704; p = 0.009), and individual and disease factors (hypertension and diabetes; OR: 1.675; 95% CI: 1.206, 2.326; p = 0.002) in the regular exercise group but not in the non-regular exercise group. This result implies that sleep quality is better with a high protein intake, even after adjusting for different confounding factors only in the regular exercise group.

Table 5. Relationship between protein intake and good sleep quality stratified by regular exercise.

    β p—Value OR 95% CI
    Lower Upper
Regular exercise Model 1 0.231 0.020 1.260 1.037 1.531
Model 2 0.305 0.009 1.357 1.081 1.704
Model3 0.516 0.002 1.675 1.206 2.326
Non-regular exercise Model 1 -0.010 0.880 0.990 0.870 1.127
Model 2 -0.006 0.925 0.994 0.868 1.137
Model 3 -0.035 0.624 0.966 0.840 1.110
Open in a new tab

Significant estimates are in bold. Model 1: adjusted for age, sex, and BMI; Model 2: adjusted for age, sex, BMI, current smoker, and current drinker; Model 3: adjusted for age, sex, BMI, hypertension, and diabetes. Abbreviations: β, coefficient; OR, odds ratio; CI, confidence interval; BMI, body mass index.

Discussion

In the present study, the PSQI was selected as the most frequently used index for sleep evaluation. Epidemiological studies on sleep have been performed using sleep times [17, 19] and questionnaires [15, 16, 18, 20, 21]. However, evaluating sleep by time alone lacks objectivity because sleep times and measurement items differ among studies. For example, one study considered the appropriate sleep time to be 7–8 hours [17], but another considered it to be 7–9 hours [19]; other studies have evaluated sleep-related time based on sleep latency (difficulty falling asleep) or sleep efficiency (maintaining sleep) [31]. Therefore, comprehensively evaluating sleep quality using a questionnaire may provide more objective findings. A previous study that compared the diagnostic screening characteristics of the Insomnia Severity Index, the Athens Insomnia Scale, and the PSQI reported similar sensitivities and specificities [32]. Therefore, the PSQI in the present study was confirmed to be a valid and comparable questionnaire to those used in other studies. Buysse et al. [28] defined a PSQI score >5 as poor sleep quality. Conversely, Das et al. [33] demonstrated that the mean PSQI was 8.59 ± 5.35 in a community-based study among a geriatric population, and they described that the difference in the PSQI may be due to the different cultures and lifestyles of people in different countries. The mean PSQI of all the participants in the present study was 10.7 ± 2.7, which seemed to reflect the current average Japanese lifestyle.

Comparisons between the PSQI ≤10 and ≥11 groups in the present study revealed that regular exercise was beneficial for sleep quality, which is consistent with previous findings [8–12, 34]. However, other studies did not observe a relationship between exercise and sleep [35, 36]. Briefly, the lowest or highest levels of exercise were not associated with sleep disorders [35], and the effects of short-term resistance exercise on sleep were inconsistent [36]. By contrast, previous studies reported a positive relationship between exercise intensity and sleep with 30 minutes or more of exercise each time [8], moderate to intense physical activity of 150 minutes or more per week [10], or 500 to 1500 metabolic equivalents of task minutes/week of physical activity [34]. Exercise intensity in the regular exercise group in the present study was considered intermediate because the mean days of exercise per week was 4.3 (SD = 1.7) and the mean exercise time per session was 80.3 minutes (SD = 64.2). Accordingly, the relationship observed between exercise intensity and sleep in the present study appears to support previous findings showing that intermediate exercise intensity has a positive effect on sleep quality.

The multiple logistic regression analysis in the present study revealed a positive correlation between good sleep quality and protein intake only in the regular exercise group. These results seem to indicate that there is a mechanism by which regular exercise promotes protein absorption. In addition to exercise, the ingestion of protein just before sleep has been reported to improve nighttime protein synthesis by enhancing its digestion and absorption [37]. Tryptophan is a constituent amino acid of protein that competes with the other larger neutral amino acids to gain access to the transport system to cross the blood-brain barrier. Dietary carbohydrates pull larger amino acids into the muscle tissue, allowing tryptophan to access the transport system, cross the blood-brain barrier, and contribute to the synthesis of serotonin and melatonin [38]. Tryptophan has been shown to affect the serotonin-melatonin pathway because an intraperitoneal injection in rats increased serotonin levels [39]; likewise, its administration to patients with moderate insomnia significantly reduced sleep latency [40]. The reason for good sleep quality among participants who reported high protein intake in their daily diet and regular exercise was thought to be a result of the pathogenesis in which the tryptophan-serotonin-melatonin pathway was activated due to the enhanced protein absorption.

In the present study, the following micronutrients were associated with sleep quality after adjusting for confounding factors (age, sex, BMI, current smoker, current drinker, education, hypertension, and diabetes): phosphorus, zinc, vitamin D, vitamin B12, and pantothenic acid. Many of these micronutrients showed similar results as previous studies [16, 17, 31]. Frank et al. reported that lower intakes of phosphorus and zinc were associated with a shorter sleep duration [31]. Komada et al. [16] reported that vitamin D and vitamin B12 in adult males were associated with sleep duration. Grandner et al. [17] reported that vitamin D was associated with sleep maintenance difficulties. Since the results for many of the micronutrients examined in the present study agreed with those of previous studies, the relationships observed between micronutrient intakes and sleep in the present study were considered reliable.

One limitation of the present study is that the number of inputs for the independent variables was restricted in the multivariate analysis because of the small number of participants. This study might include selection bias because the subjects participated voluntarily in this study. Since the PSQI was evaluated only with a questionnaire, using a more objective method such as a polysomnogram to assess sleep quality is necessary. Since we have not examined the effects of obstructive sleep apnea, future studies should be performed that incorporate a design to evaluate obstructive sleep apnea. Moreover, since this was a cross-sectional study, interventions analyzing regular exercise and protein intake could not be conducted. Further multicenter randomized controlled trials with target values for exercise intensity and protein intake are necessary to clarify the effects of regular exercise and nutrient intake on sleep quality.

Conclusions

We conducted this cross-sectional study on Japanese participants to investigate the relationship between regular exercise and nutrient intake as factors affecting sleep quality. Protein intake was higher among the participants with a PSQI ≤10 in the regular exercise group (mean, 17.13% of energy consumption) than in those in the non-regular exercise or PSQI ≥11 groups. Furthermore, the results of the multiple logistic regression analysis showed that sleep quality was better in the regular exercise group when protein intake was high; this relationship was not observed in the non-regular exercise group.

Supporting information

S1 Fig. Interaction between regular exercise and the PSQI on protein intake.

* Post hoc Bonferroni analysis. Adjusted for age = 60.54, sex = 1.51, BMI = 23.05, current smoker = 1.83, current drinker = 1.42, education = 2.32, hypertension = 1.67, diabetes = 1.92. Error bar: 95% CI. Abbreviations: PSQI, Pittsburgh Sleep Quality Index, EMMEANS, estimated marginal means.

(TIF)

Click here for additional data file. (3.9MB, tif)

Acknowledgments

We would like to thank the officials of Shika Town, Ishikawa prefecture and the staff of the Department of Environmental and Preventive Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa University Graduate School of Advanced Preventive Medical Sciences, Department of Bioinformatics and Genomics, University of Tsukuba and Keio University.

Data Availability

The data described in the manuscript will be made available upon request, application and approval (Kanazawa University Ethics Committee. Person in charge: Yuko Katsuragi <pub-jim2@staff.kanazawa-u.ac.jp>).

Funding Statement

The present study was supported by a Grant-in-Aid for Scientific Research (B) by the Ministry of Education, Culture, Sport, Science and Technology (MEXT), number 15H04783 and 16H03245. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Decision Letter 0

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PONE-D-20-33985

Protein intake in inhabitants with regular exercise is associated with sleep quality: Result of the Shika study

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I have read with great interest the study of Fumihiko Suzuki and collaborators and I want to comment the following:

1. I am struck by the division of two study groups based on a cut-off point of 10 in the PSQI without a clinical justification.

The original PSQI study concluded that a value greater than 5 indicates a negative impact on sleep. This data is mentioned by the authors in the methodology. However, it makes no mention of the Japanese validation study that found similar data. That is, values >5.5 are indicative of poor sleep quality. By the way, in the study the control group had an average 38 years old and a cut-off point of 7.5, a specificity of 97% was found for those patients with primary insomnia. Then, an average of 10 points seems to be high and difficult to be considered normal. (Doi Y, Minowa M, Uchiyama M, Okawa M, Kim K, Shibui K, et al. Psychometric assessment of subjective sleep quality using the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) in psychiatric disordered and control subjects. Psychiatry Res. 2000;97: 165–172.)

The authors could use the cutoff points that best fit their purposes, but as a post-frame analysis. In strict adherence to the above, it would be desirable for the researchers to add an analysis considering the cut-off point of> 5.5 and continue with the groups they consider.

2. The discussion should mention the possible causes for which the average population has poor sleep quality (mean PSQI of 10) and be careful to consider the group with <10 as having a good quality of sleep.

Reviewer #2: the manuscript is well written with novel findings

comments:

methodology:

the author needs to define what is PSQI and BDHQ and did you use Japanese version and if so, any validation study done

Results:

good analysis was done

Discussion:

PSQI has its own drawback for sleep quality assessment. furthermore, people with metabolic syndrome are at greater risk of developing obstructive sleep apnea and that may hinder their sleep quality

please add these comments in the discussion

**********

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Reviewer #1: No

Reviewer #2: No

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Decision Letter 1

Jose M Moran

11 Feb 2021

PONE-D-20-33985R1

Protein intake in inhabitants with regular exercise is associated with sleep quality: Result of the Shika study

PLOS ONE

Dear Dr. Suzuki,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Although authors have appropriately addressed the requirements of the reviewers, before recommending publication of the article, and given that the authors have included in their analysis the t-Student, ANCOVA, multiple linear regression and Pearson correlations, the authors should state in the methodology section that all the variables involved fulfilled the assumptions required by parametric methods and that these were tested by the appropriate tests (indicate which ones the authors have used).

Please submit your revised manuscript by Mar 28 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

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We look forward to receiving your revised manuscript.

Kind regards,

Jose M. Moran

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors' response to the observation of the cut-off points is valid because they are supported by a recent report on the geriatric population and therefore responds favorably to the question about the high value of the Pittsburgh sleep quality scale in the population of this study.

Reviewer #2: minor linguistic errors,

i would suggest writing a review linking, sleep, exercise fitness and diet. the focus on sleep not only from OSA prospective but rather descriping the link between sleep duration, timing and physical fitness in addition to healthy diet

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: Mohammed A. Al-Abri

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2021 Feb 26;16(2):e0247926. doi: 10.1371/journal.pone.0247926.r004

Author response to Decision Letter 1

16 Feb 2021

Feb 16th, 2021.

Jose M. Moran, Ph. D

Academic Editor

PLOS ONE

Dear Dr. Moran,

Thank you for inviting us to submit a revised draft of our manuscript entitled, “Protein intake in inhabitants with regular exercise is associated with sleep quality: Results of the Shika study” to PLOS ONE. We also appreciate the time and effort you and each of the reviewers have dedicated to providing insightful feedback on ways to strengthen our paper. Thus, it is with great pleasure that we resubmit our article for further consideration. We have incorporated changes that reflect the detailed suggestions you have graciously provided. We also hope that our edits and the responses we provide below satisfactorily address all the issues and concerns you and the reviewers have noted.

To facilitate your review of our revisions, the following are our point-by-point responses to the questions and comments delivered in your letter dated Feb 11th, 2020.

Major points.

Q1. Although authors have appropriately addressed the requirements of the reviewers, before recommending publication of the article, and given that the authors have included in their analysis the t-Student, ANCOVA, multiple linear regression and Pearson correlations, the authors should state in the methodology section that all the variables involved fulfilled the assumptions required by parametric methods and that these were tested by the appropriate tests (indicate which ones the authors have used).

A1. We have added the following phrase to the revised manuscript: “The distribution of variables was checked by the Kolmogorov–Smirnov, and Shapiro–Wilk normality tests, or the normal distribution curve in the histogram was confirmed before using other statistical tests.” (P9 L180–182).

Supplementary explanation: Although some variables had a p-value of 0.05 or less in the Kolmogorov–Smirnov, and Shapiro–Wilk normality test, it was confirmed that a normal distribution curve was drawn in the histogram. Therefore, we believe that the variables used in this study can be expected to have a multivariate normal distribution.

Reviewer #1:

There were no additional comments.

Reviewer #2

Q1. Has the statistical analysis been performed appropriately and rigorously? (Reviewer #2: I Don't Know)

A1. We have added the following phrase to the revised manuscript: “The distribution of variables was checked by the Kolmogorov–Smirnov, and Shapiro–Wilk normality tests, or the normal distribution curve in the histogram was confirmed before using other statistical tests.” (P9 L180–182).

Supplementary explanation: Although some variables had a p-value of 0.05 or less in the Kolmogorov–Smirnov, and Shapiro–Wilk normality test, it was confirmed that a normal distribution curve was drawn in the histogram. Therefore, we believe that the variables used in this study can be expected to have a multivariate normal distribution.

Q2. minor linguistic errors,

i would suggest writing a review linking, sleep, exercise fitness and diet. the focus on sleep not only from OSA prospective but rather descriping the link between sleep duration, timing and physical fitness in addition to healthy diet.

A2. Since we were conducting a cross-sectional analysis, we cannot examine the sleep duration and timing in detail, but the mechanism by which regular exercise and nutrition on sleep quality were described as follows: "The reason for good sleep quality among participants who reported high protein intake in their daily diet and regular exercise was thought to be a result of the pathogenesis in which the tryptophan-serotonin-melatonin pathway was activated due to the enhanced protein absorption" (P20 L348-351).

Again, thank you for giving us the opportunity to strengthen our manuscript with your valuable comments and queries. We have worked hard to incorporate your feedback and hope that these revisions persuade you to accept our submission.

Sincerely,

Fumihiko Suzuki

Department of Environmental and Preventive Medicine, Graduate School of Medical Science, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan.

Tel: +81-76-265-2218

Email address: f-suzuki@stu.kanazawa-u.ac.jp

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file. (20.6KB, docx)

Decision Letter 2

Jose M Moran

17 Feb 2021

Protein intake in inhabitants with regular exercise is associated with sleep quality: Result of the Shika study

PONE-D-20-33985R2

Dear Dr. Suzuki,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Jose M. Moran

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Jose M Moran

19 Feb 2021

PONE-D-20-33985R2

Protein intake in inhabitants with regular exercise is associated with sleep quality: Results of the Shika study

Dear Dr. Suzuki:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Jose M. Moran

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Fig. Interaction between regular exercise and the PSQI on protein intake.

    * Post hoc Bonferroni analysis. Adjusted for age = 60.54, sex = 1.51, BMI = 23.05, current smoker = 1.83, current drinker = 1.42, education = 2.32, hypertension = 1.67, diabetes = 1.92. Error bar: 95% CI. Abbreviations: PSQI, Pittsburgh Sleep Quality Index, EMMEANS, estimated marginal means.

    (TIF)

    Click here for additional data file. (3.9MB, tif)
    Attachment

    Submitted filename: Response to Reviewers.docx

    Click here for additional data file. (27.6KB, docx)
    Attachment

    Submitted filename: Response to Reviewers.docx

    Click here for additional data file. (20.6KB, docx)

    Data Availability Statement

    The data described in the manuscript will be made available upon request, application and approval (Kanazawa University Ethics Committee. Person in charge: Yuko Katsuragi <pub-jim2@staff.kanazawa-u.ac.jp>).

    Articles from PLoS ONE are provided here courtesy of PLOS

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