Abstract
Study Objectives:
Insomnia and snoring are common sleep disorders. The aim was to investigate the association of having a combination of insomnia symptoms and snoring with comorbidity and daytime sleepiness.
Methods:
The study population comprised 25,901 participants (16–75 years, 54.4% women) from 4 Swedish cities, who answered a postal questionnaire that contained questions on snoring, insomnia symptoms (difficulties initiating and/or maintaining sleep and/or early morning awakening), smoking, educational level, and respiratory and nonrespiratory disorders.
Results:
Snoring was reported by 4,221 (16.2%), while 9,872 (38.1%) reported ≥ 1 insomnia symptom. A total of 2,150 (8.3%) participants reported both insomnia symptoms and snoring. The association with hypertension (adjusted odds ratio [OR], 1.4; 95% confidence interval [CI], 1.2–1.6), chronic obstructive pulmonary disease (adjusted OR, 1.8; 95% CI, 1.3–2.4), asthma (adjusted OR, 1.9; 95% CI, 1.6–2.3), daytime sleepiness (adjusted OR, 7.9; 95% CI, 7.1–8.8), and the use of hypnotics (adjusted OR, 7.5; 95% CI, 6.1–9.1) was highest for the group with both insomnia symptoms and snoring.
Conclusions:
Participants with both snoring and insomnia run an increased risk of hypertension, chronic obstructive pulmonary disease, asthma, daytime sleepiness, and use of hypnotics. It is important to consider snoring in patients seeking medical assistance for insomnia and, vice versa, in patients with snoring inquiring about insomnia.
Citation:
Hägg SA, Ilieva E, Ljunggren M, et al. The negative health effects of having a combination of snoring and insomnia. J Clin Sleep Med. 2022;18(4):973–981.
Keywords: snoring, insomnia, daytime sleepiness, hypertension, COPD, asthma
BRIEF SUMMARY
Current Knowledge/Study Rationale: Insomnia and snoring are common in the general population, and there is a considerable overlap between these conditions. Both conditions are independently associated with negative health effects, but very little is known about the effects of a combination of insomnia and snoring.
Study Impact: We found that having both insomnia symptoms and snoring is associated with more comorbidity and daytime sleepiness, a finding that is clinically important. One patient can be afflicted by more than 1 sleep disturbance, which must be considered to be able to help the patient in the best possible manner.
INTRODUCTION
Insomnia and snoring are common complaints in the general population, reported by 6%–10%1,2 and 20%–40%,3,4 respectively. Insomnia is characterized by a disturbance of nocturnal sleep by 1 or more of the following complaints: difficulty initiating sleep, difficulty maintaining sleep, or early morning awakening, with related daytime impairment.5 Snoring is a symptom of increased upper airway resistance and the need for greater respiratory effort for the maintenance of ventilation, and it is one of the cardinal symptoms of sleep-disordered breathing (SDB). Even though the majority of snorers do not fulfill the diagnostic criteria for obstructive sleep apnea (OSA), snoring may be regarded as part of the spectrum of SDB due to the increased respiratory effort. Furthermore, snoring is independently associated with negative health effects, such as carotid atherosclerosis6 and increased all-cause mortality.7 Snoring is associated with daytime sleepiness, even in the absence of sleep apnea,8 and daytime sleepiness is included in the criteria for a diagnosis of insomnia.5 The standard treatment for insomnia is cognitive behavioral therapy, although the addition of hypnotics can be effective, at least for short-term treatment.9
As patients seek medical advice for snoring and if their OSA status is unknown, it is of interest to further examine risks associated with snoring per se. The combination of snoring and insomnia is of special interest since both are common sleep complaints that are independently associated with negative health effects. Some studies have been conducted regarding the effects of the overlap between insomnia and OSA,10–16 but very little is known about the effects of having a combination of insomnia and snoring. A recent study found that sleep quality, as measured by polysomnography, was impaired in women with both insomnia and snoring compared with those with only 1 of these sleep disturbances.17 This raises the question of whether insomnia symptoms and snoring also exert an effect on the risk of comorbid disease and daytime impairment. As far as we know, this has not previously been analyzed in a nonclinical, population-based sample.
Aim
The aim of this study was to investigate the association of having a combination of insomnia symptoms and snoring with comorbidities and daytime consequences in a large-scale, nonclinical general population. Our hypothesis was that the combination of both symptoms has a greater association with the prevalence of cardiovascular and pulmonary comorbidities, daytime sleepiness, and the use of hypnotics than having only snoring or only insomnia symptoms.
METHODS
Study population
The Global Allergy and Asthma Network of Excellence (GA2LEN) is a multinational European research network focusing primarily on asthma and allergic diseases.18 The GA2LEN survey was conducted in 2008, when a postal questionnaire was sent to randomly selected participants in the population. The questionnaire included questions on airway disease, allergic diseases, comorbidities, eczema, educational and occupational status, sleep, daytime sleepiness, and lifestyle factors.19 The Swedish version of the survey consisted of 40 questions and was sent to a total of 45,000 individuals aged 16–75 years in 4 major Swedish cities (Gothenburg, Stockholm, Umeå, and Uppsala). After up to 3 reminders, 26,675 participants answered the survey (response rate 59.2%).19 The current study cohort consists of the participants who answered the questions regarding both snoring and insomnia symptoms.
Informed consent was obtained from each participant, and ethical approval was granted by the Regional Ethical Review Board in Uppsala (2008/014).
Definitions
Sleep-related symptoms and medication
Questions from the Basic Nordic Sleep Questionnaire were used to assess sleep-related symptoms and daytime symptoms.20 The participants were asked about the frequency of symptoms during the last few months. The included symptoms were as follows: “difficulty falling asleep,” “difficulty maintaining sleep,” “early morning awakening,” “loud and disturbing snoring,” and “daytime sleepiness.” The response options were on a scale of 1–5: (1) never or very seldom, (2) less than once a week, (3) once to twice a week, (4) 3 to 5 times a week, and (5) every day or almost every day of the week. Participants reporting difficulty inducing sleep, difficulty maintaining sleep, or early morning awakening ≥ 3 times a week (scores of 4 and 5) were regarded as having insomnia symptoms.21,22 Participants were regarded as snorers if they stated they snored ≥ 3 times a week (scores of 4 and 5). Excessive daytime sleepiness was defined as having daytime sleepiness ≥ 3 times a week. Based on the responses to the questions on insomnia symptoms and snoring, the participants were further categorized as follows: “No snoring, no insomnia,” “Snorers without insomnia symptoms,” “Insomnia symptoms without snoring,” and “Snorers with insomnia symptoms.”
A positive answer to the question “Are you currently taking medication for sleeping problems?” was defined as the use of “hypnotics.”
Comorbid disease
An affirmative answer to the question “Are you currently taking medication for high blood pressure/diabetes?” was used to define participants with hypertension or diabetes, respectively.
Chronic obstructive pulmonary disease (COPD) was defined as a positive answer to 1 or both of the following questions: “Has a doctor ever told you that you have chronic obstructive pulmonary disease?” and “Are you currently taking medication for chronic obstructive pulmonary disease?” Current asthma was defined as an affirmative answer to either “Have you had an asthma attack in the last 12 months?” or “Are you currently taking any medication for asthma, including inhalers, aerosols, or tablets?”19,21–23
Covariates
Positive answers to both “Have you ever smoked 1 or more cigarettes a day for more than 1 year?” and “Have you smoked at all during the last month?” were used to define patients as current smokers. Participants were regarded as never-smokers if they responded negatively to both questions, and as ex-smokers if they stated that they had smoked for more than 1 year but not during the last month.21,23 Body mass index (BMI) was calculated as self-reported body weight (kg) divided by self-reported height (m) squared (kg/m2). Educational level was derived from the answer to “What is your highest level of education?” and divided into the following categories: “elementary school,” “high school,” or “university.” Elementary school was defined as any education below the level of high school. Depending on the answer to “How often do you exercise resulting in breathlessness or sweating?” the participants were divided into the following groups: “inactive” (once/month or less), “moderately active” (1–3 times/week), or “vigorously active” (≥ 4 times/week).
Statistical analysis
Stata version 15.1 (StataCorp, College Station, TX) was used in all statistical analyses. P values < .05 were considered statistically significant. The results are presented as unadjusted/adjusted odds ratios (ORs) with 95% confidence intervals (CIs).
One-way ANOVA (analysis of variance) and unpaired t test were used for comparisons of continuous variables between the groups, while chi-square test was used to analyze differences in categorical variables. Multiple logistic regression analyses adjusted for the variables of age, smoking status, BMI, physical activity level, and educational level were performed.
RESULTS
The study population comprised 25,901 participants who had responded to questions regarding both insomnia symptoms and snoring. Of the study population, 4,221 (16.2%) reported snoring and 9,872 (38.1%) had at least 1 insomnia symptom.
Snorers were more often male, were older, had a higher BMI, were smokers, and had a lower educational level and less physical activity compared with nonsnorers (Table 1). Compared with nonsnorers, snorers had a higher prevalence of all sleep-related symptoms. Participants with insomnia symptoms were older, had a higher BMI, and were more often female and smokers than those without insomnia symptoms (Table 1). They also had a lower educational level and were less physically active. Snoring was more common in those with insomnia symptoms than in those without.
Table 1.
Characteristics of the cohort.
| All (n = 25,901) | Snoring | Insomnia Symptoms | |||||
|---|---|---|---|---|---|---|---|
| Yes (n = 4,221) | No (n = 21,680) | P | Yes (n = 9,872) | No (n = 16,029) | P | ||
| Age, y | 43.4 (16.0) | 50.0 (13.9) | 42.1 (16.1) | < .001 | 46.2 (15.9) | 41.7 (15.8) | < .001 |
| BMI, kg/m2 | 24.7 (4.1) | 27.1 (4.6) | 24.3 (3.9) | < .001 | 25.2 (4.5) | 24.4 (3.9) | < .001 |
| Sex | < .001 | < .001 | |||||
| Male | 11,784 (45.6) | 2,638 (62.7) | 9,146 (42.3) | 4,064 (41.3) | 7,720 (48.3) | ||
| Female | 14,064 (54.4) | 1,573 (37.4) | 12,491 (57.7) | 5,785 (58.7) | 8,279 (51.8) | ||
| Smoking status | < .001 | < .001 | |||||
| Never-smoker | 15,619 (61.1) | 1,915 (46.3) | 13,704 (64.1) | 5,293 (54.4) | 10,326 (62.3) | ||
| Former smoker | 6,347 (24.8) | 1,394 (33.6) | 4,953 (23.2) | 2,896 (29.8) | 3,451 (21.8) | ||
| Current smoker | 3,582 (14.0) | 842 (20.3) | 2 740 (12.8) | 1,533 (15.8) | 2,049 (13.0) | ||
| Snoring | 4,221 (16.3) | — | — | 2,150 (21.8) | 2,071 (12.9) | < .001 | |
| Insomnia symptoms | 9,872 (38.1) | 2,150 (50.9) | 7,722 (35.6) | < .001 | — | — | |
| Difficulty initiating sleep | 3,648 (14.1) | 822 (19.5) | 2,826 (13.0) | < .001 | 3,648 (37.0) | — | |
| Difficulty maintaining sleep | 7,307 (28.2) | 1,688 (40.0) | 5,619 (25.9) | < .001 | 7,307 (74.0) | — | |
| Early morning awakening | 3,902 (15.1) | 986 (23.4) | 2,916 (13.4) | < .001 | 3,902 (39.5) | — | |
| Excessive daytime sleepiness | 7,745 (30.0) | 1,671 (40.6) | 6,074 (28.0) | < .001 | 4,742 (48.0) | 3,003 (18.7) | < .001 |
| Hypertension | 3,213 (12.7) | 867 (21.3) | 2,346 (11.0) | < .001 | 1,580 (16.7) | 1,633 (10.3) | < .001 |
| Diabetes | 746 (3.1) | 210 (5.6) | 536 (2.6) | < .001 | 364 (4.1) | 382 (2.5) | < .001 |
| COPD | 380 (1.6) | 101 (2.7) | 279 (1.4) | < .001 | 216 (2.3) | 164 (1.1) | < .001 |
| Asthma | 1,803 (7.2) | 359 (8.9) | 1,444 (6.9) | < .001 | 850 (9.0) | 953 (6.2) | < .001 |
| Hypnotics | 1,391 (5.7) | 338 (8.9) | 1,053 (5.1) | < .001 | 1,138 (12.4) | 253 (1.7) | < .001 |
| Educational level | < .001 | < .001 | |||||
| Elementary school | 13.018 (50.5) | 807 (19.2) | 3,151 (14.6) | 1,780 (18.1) | 2,178 (13.7) | ||
| High school | 8,794 (34.1) | 1,568 (17.8) | 7,226 (33.5) | 3,260 (33.2) | 5,534 (34.7) | ||
| University | 3,958 (15.4) | 1,827 (43.5) | 11,191 (51.9) | 4,777 (48.7) | 8,241 (51.7) | ||
| Physical activity | < .001 | < .001 | |||||
| Inactive | 6,896 (26.7) | 1,452 (34.6) | 5,444 (25.2) | 2,902 (29.6) | 3,994 (25.0) | ||
| Moderately active | 14,217 (55.1) | 2,120 (50.5) | 12,097 (56.0) | 5,133 (52.3) | 9,084 (56.9) | ||
| Vigorously active | 4,682 (18.2) | 625 (14.9) | 4,057 (18.8) | 1,782 (18.2) | 2,900 (18.2) | ||
Data are presented as mean ± standard deviation or n (%). P values were calculated with the unpaired t test and the chi-square test. BMI = body mass index, COPD = chronic obstructive pulmonary disease.
Of the participants reporting insomnia symptoms, 21.8% also reported snoring. Of the snorers, 50.9% also reported insomnia symptoms. Of the total study population, 8.3% (n = 2,150) reported having both insomnia symptoms and snoring (Figure 1).
Figure 1. Venn diagram depicting individuals with snoring, insomnia, and the combination of the 2.
Participants with a combination of snoring and insomnia symptoms were older, had a higher BMI, and were more often smokers than those not reporting either snoring or insomnia symptoms or reporting only 1 of the 2 symptoms (Table 2). Furthermore, they had a lower educational level and were more often physically inactive. They also reported more daytime sleepiness and a higher prevalence of the comorbidities; hypertension, asthma, COPD, and diabetes (Table 2).
Table 2.
Characteristics of the groups with no insomnia symptoms or snoring, only snoring, only insomnia symptoms, and snoring and insomnia symptoms.
| No Snoring, No Insomnia Symptoms (n = 13,958) | Snoring, No Insomnia Symptoms (n = 2,071) | Insomnia Symptoms, No Snoring (n = 7,772) | Snoring and Insomnia Symptoms (n = 2,150) | P | |
|---|---|---|---|---|---|
| Age, y | 40.7 (15.8) | 48.2 (14.0) | 44.7 (16.1) | 51.7 (13.6) | < .001 |
| BMI, kg/m2 | 24.1 (3.4) | 26.8 (4.4) | 24.6 (4.2) | 27.3 (4.8) | < .001 |
| Sex | < .001 | ||||
| Male | 6,288 (45.1) | 1,432 (69.4) | 2,858 (37.1) | 1,206 (56.2) | |
| Female | 7,646 (54.9) | 633 (30.7) | 4,845 (62.9) | 940 (43.8) | |
| Smoking status | < .001 | ||||
| Never-smoker | 9,308 (67.5) | 1,018 (49.9) | 4,396 (57.8) | 897 (42.5) | |
| Former smoker | 2,808 (20.4) | 643 (31.5) | 2,145 (28.2) | 751 (35.6) | |
| Current smoker | 1,669 (12.1) | 380 (18.6) | 1,071 (14.1) | 462 (21.9) | |
| Excessive daytime sleepiness | 2,481 (17.8) | 522 (25.2) | 3,592 (46.5) | 1,149 (53.4) | < .001 |
| Hypnotics | 209 (1.6) | 44 (2.3) | 844 (11.7) | 294 (15.4) | < .001 |
| Educational level | < .001 | ||||
| Elementary school | 1,844 (13.3) | 334 (16.2) | 1,307 (17.0) | 473 (22.2) | |
| High school | 4,740 (34.1) | 794 (38.4) | 2,486 (32.4) | 774 (36.3) | |
| University | 7,203 (52.6) | 939 (45.4) | 3,889 (50.6) | 888 (41.6) | |
| Physical activity | |||||
| Inactive | 3,304 (23.8) | 690 (33.4) | 2,140 (27.8) | 762 (35.8) | |
| Moderately active | 7,991 (57.4) | 1,093 (52.9) | 4,106 (53.4) | 1,027 (48.2) | |
| Vigorously active | 2,617 (18.8) | 283 (13.7) | 1,440 (18.7) | 342 (16.1) |
Data are presented as mean ± standard deviation or n (%). P values were calculated for differences with the unpaired t test and the chi-square test. BMI = body mass index.
Both snoring and insomnia were associated with a higher prevalence of hypertension, asthma, COPD, and diabetes (Table 1). The prevalence of hypertension, diabetes, COPD, and asthma was highest in the group reporting a combination of snoring and insomnia symptoms (Figure 2).
Figure 2. Prevalence of comorbidities (hypertension, diabetes, COPD, asthma) in relation to the presence of snoring and/or insomnia symptoms.
COPD = chronic obstructive pulmonary disease.
The OR for hypertension, diabetes, COPD, and asthma was the highest in the group with a combination of snoring and insomnia symptoms. For hypertension and diabetes, the OR was higher in the group with only snoring than in the group with only insomnia symptoms, while the group with only insomnia symptoms had a higher OR for COPD and asthma (Table 3). The association remained significant for hypertension, COPD, and asthma, while there was a borderline association for diabetes after adjustment for confounding factors (Table 4).
Table 3.
Association between snoring, insomnia, and comorbidities.
| Hypertension (n = 3,213) | Diabetes (n = 746) | COPD (n = 380) | Asthma (n = 1,803) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| OR | 95% CI | P | OR | 95% CI | P | OR | 95% CI | P | OR | 95% CI | P | |
| No snoring, no insomnia symptoms | 1.0 | 1.0 | 1.0 | 1.0 | ||||||||
| Snoring, no insomnia symptoms | 2.02 | 1.78–2.30 | < .001 | 2.98 | 1.54–2.54 | < .001 | 1.58 | 1.06–2.35 | .024 | 1.19 | 1.00–1.43 | .064 |
| Insomnia symptoms, no snoring | 1.62 | 1.49–1.77 | < .001 | 1.51 | 1.27–1.80 | < .001 | 2.06 | 1.63–2.61 | < .001 | 1.46 | 1.31–1.63 | < .001 |
| Snoring and insomnia symptoms | 3.33 | 3.00–3.74 | < .001 | 3.23 | 2.61–4.00 | < .001 | 4.00 | 3.00–5.33 | < .001 | 1.86 | 1.54–2.18 | < .001 |
Results are from logistic regression, univariate analyses. Separate logistic regressions were conducted for each comorbidity. The results are presented as ORs and 95% CIs. CI = confidence interval, COPD = chronic obstructive pulmonary disease, OR = odds ratio.
Table 4.
Results of multiple logistic regression for the association between snoring, insomnia, and comorbidities after adjustment for confounding factors.
| Hypertension (n = 3,213) | Diabetes (n = 746) | COPD (n = 380) | Asthma (n = 1,803) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ORadj | 95% CI | P | ORadj | 95% CI | P | ORadj | 95% CI | P | ORad | 95% CI | P | |
| No snoring, no insomnia symptoms | 1.0 | 1.0 | 1.0 | 1.0 | ||||||||
| Snoring, no insomnia symptoms | 1.10 | 0.94–1.28 | .240 | 0.96 | 0.73–1.25 | .753 | 1.00 | 0.66–1.51 | .997 | 1.25 | 1.03–1.53 | .023 |
| Insomnia symptoms, no snoring | 1.22 | 1.10–1.35 | < .001 | 1.13 | 0.93–1.36 | .210 | 1.49 | 1.16–1.92 | .002 | 1.45 | 1.30–1.63 | < .001 |
| Snoring and insomnia symptoms | 1.41 | 1.23–1.63 | < .001 | 1.25 | 0.99–1.59 | .064 | 1.78 | 1.27–2.42 | .001 | 1.91 | 1.61–2.27 | < .001 |
| Age | 1.11 | 1.11–1.12 | < .001 | 1.06 | 1.06–1.07 | < .001 | 1.07 | 1.06–1.08 | < .001 | 1.00 | 0.98–0.99 | < .001 |
| Male | 1.06 | 0.96–1.16 | .245 | 1.60 | 1.36–1.88 | < .001 | 0.81 | 0.65–1.01 | .066 | 0.71 | 0.64–0.79 | < .001 |
| BMI | 1.3 | 1.11–1.14 | < .001 | 1.14 | 1.12–1.15 | < .001 | 1.03 | 1.00–1.06 | .023 | 1.05 | 1.04–1.06 | < .001 |
| Smoking status | ||||||||||||
| Never-smoker | 1.0 | 1.0 | 1.0 | 1.0 | ||||||||
| Former smoker | 1.17 | 1.05–1.28 | .004 | 1.09 | 0.91–1.30 | .352 | 2.27 | 1.73–2.98 | < .001 | 1.11 | 1.0–1.3 | .072 |
| Current smoker | 1.23 | 1.08–1.40 | .002 | 1.12 | 0.90–1.42 | .328 | 4.11 | 3.07–5.51 | < .001 | 0.88 | 0.99–1.27 | .111 |
| Educational level | ||||||||||||
| University | 1.0 | 1.0 | 1.0 | 1.0 | ||||||||
| High school | 1.17 | 1.05–1.30 | .005 | 1.22 | 1.00–1.50 | .053 | 1.71 | 1.29–2.27 | < .001 | 1.11 | 0.99–1.27 | .067 |
| Elementary school | 1.41 | 1.26–1.58 | < .001 | 2.18 | 1.79–2.67 | < .001 | 2.60 | 1.96–3.42 | < .001 | 1.17 | 0.99–1.24 | .043 |
| Physical activity | ||||||||||||
| Vigorously active | 1.0 | 1.0 | 1.0 | 1.0 | ||||||||
| Moderately active | 0.94 | 0.83–1.06 | .294 | 0.68 | 0.55–0.85 | < .001 | 0.81 | 0.60–1.09 | .165 | 0.76 | 0.67–0.86 | < .001 |
| Inactive | 0.95 | 0.83–1.08 | .429 | 0.88 | 0.70–1.10 | .280 | 0.90 | 0.67–1.23 | .513 | 0.70 | 0.60–0.81 | < .001 |
Separate logistic regressions were conducted for each comorbidity. The results are presented as ORs and 95% CIs after adjustment for age, sex, BMI, smoking status, educational level, and physical activity. BMI = body mass index, CI = confidence interval, COPD = chronic obstructive pulmonary disease, OR = odds ratio, ORadj = adjusted odds ratio.
Excessive daytime sleepiness was reported by 29.9% of the total study population (n = 7,745). In the group with no snoring or insomnia symptoms, 17.7% reported excessive daytime sleepiness, while 53.4% of the group with both snoring and insomnia symptoms reported excessive daytime sleepiness.
Compared with the other groups, the group with both snoring and insomnia had the highest OR for both excessive daytime sleepiness and the use of hypnotics. The association remained after adjustment for confounding factors. After adjustment, the OR for excessive daytime sleepiness in the group with a combination of snoring and insomnia symptoms was 7.9 (95% CI, 7.09–8.80), while the OR was 7.5 for those taking hypnotics (95% CI, 6.12–9.10) (Table 5).
Table 5.
Results of multiple logistic regression for the association between snoring, insomnia, and excessive daytime sleepiness and the use of hypnotics.
| Excessive Daytime Sleepiness (n = 7,745) | Hypnotics (n = 1,391) | |||||
|---|---|---|---|---|---|---|
| ORadj | 95% CI | P | ORadj | 95% CI | P | |
| No snoring, no insomnia symptoms | 1.0 | 1.0 | ||||
| Snoring, no insomnia symptoms | 2.04 | 1.18–2.30 | < .001 | 1.18 | 0.84–1.65 | .348 |
| Insomnia symptoms, no snoring | 4.78 | 4.46–5.10 | < .001 | 7.01 | 6.00–8.24 | < .001 |
| Snoring and insomnia symptoms | 7.90 | 7.09–8.80 | < .001 | 7.46 | 6.12–9.10 | < .001 |
Separate logistic regressions were conducted for each outcome. The results are presented as ORs and 95% CIs after adjustment for age, sex, BMI, smoking status, educational level, and physical activity. BMI = body mass index, CI = confidence interval, OR = odds ratio, ORadj = adjusted odds ratio.
For the group having both snoring and insomnia symptoms, there was a significant interaction with age for the outcomes of hypertension (P = .006) and the use of hypnotics (P = .006), with a stronger association in the < 50-year age group. In contrast, for daytime sleepiness, the association was more pronounced in participants > 50 years (P for interaction < .001).
DISCUSSION
In this large-scale, population-based study, we found that a combination of self-reported snoring and insomnia symptoms has an effect on comorbid hypertension, asthma, and COPD compared with those with only snoring or insomnia symptoms alone. In addition, excessive daytime sleepiness and the use of hypnotics were more common in the group with both insomnia symptoms and snoring.
Interaction between snoring and insomnia
The interaction between SDB and insomnia is thought to take place via various routes, and it has not yet been established whether 1 condition has a causal effect on the other or whether they are merely mutually potentiating. Patients with insomnia, in their hyperarousal state, have a lower respiratory arousal threshold, which may cause an earlier response to the increased respiratory resistance in SDB than in those without insomnia, leading to increased fragmentation of sleep and ventilation stability, which, in turn, increases the risk of upper airway obstruction.24 Sleep fragmentation and arousals caused by SDB may more often be perceived as wakefulness in those with insomnia than in those without insomnia.25 Then, due to hyperarousal, they have more difficulty falling back into a deep sleep, leading to the further re-enforcement of hyperarousal. Other symptoms of SDB, such as nocturia and excessive daytime sleepiness, may cause sleep disruption and lead to compensatory daytime behaviors (increased caffeine intake, daytime napping), which, in turn, may lead to increased difficulty inducing and maintaining sleep and even more daytime sleepiness. The increased insomnia symptoms may also lead to increased use of hypnotics in an attempt to improve sleep quality. Finally, hypnotics can cause daytime sleepiness due to a residual sedative effect.26
Snoring, insomnia, and hypertension
Snoring and insomnia symptoms were both independently associated with an increased risk of having hypertension, and the combination of the 2 conditions showed the highest adjusted OR. Comparable studies of snoring and insomnia are lacking. The combination of OSA and insomnia has been analyzed in a few previous studies, with varying results regarding the additional effect of OSA and insomnia on hypertension prevalence. Moreover, if one considers snoring as a part of the SDB continuum, it is reasonable that the same mechanism applies as for OSA.13–16 Vozoris13 and Björnsdóttir et al16 did not find that individuals with sleep apnea and insomnia had a higher risk of hypertension, while Saaresranta et al14 found that cardiovascular disease was more prevalent in the OSA group with insomnia. Furthermore, Gupta and Knapp15 found that the OSA and insomnia group had a higher frequency of hypertension. The conflicting results may depend, in part, on different study methodology, different study populations, and different definitions of OSA and insomnia.
Blood pressure has a circadian variability, and changes in the autonomic control of circulation during normal sleep cause a blood pressure dip.27 Disrupted sleep can lead to a nondipping blood pressure pattern, which is associated with a poorer cardiovascular outcome.28 In SDB, the narrowing of the upper airways during sleep, intermittent hypoxia, and arousals lead to increased sympathetic activity and activation of the renin-angiotensin-aldosterone system and the hypothalamus-pituitary-adrenal axis, contributing to the development of hypertension.29 Insomnia is regarded as a state of hyperarousal, with changes in hormonal balance, increased sympathetic activity, and hypothalamus-pituitary-adrenal axis activation, leading to metabolic changes and hypertension.30 Our results suggest that the more disrupted the sleep quality, the greater the effect on cardiometabolic disease (hypertension and diabetes), as shown by the significantly increased prevalence of hypertension that we found and the borderline significance of the prevalence of diabetes.
Snoring, insomnia, and obstructive lung disease
With regard to asthma, the highest risk was found in the group that had reported both snoring and insomnia symptoms; the relationship is most likely bidirectional. OSA is believed to exacerbate asthma through various mechanisms, including neuromechanical reflex broncho-obstruction and gastroesophageal reflux.31 Conversely, asthma is thought to contribute to the development of incident OSA, possibly by way of inflammation.32–34 In a study by Brumpton et al,35 they found an increased risk of developing asthma in those with chronic insomnia compared with those without, possibly by way of the proinflammatory character of insomnia. Conversely, asthma symptoms and associated rhinitis may act as precipitating factors for the onset of insomnia symptoms.21 Insomnia symptoms may persist even in those with well-controlled asthma.36 Cough, shortness of breath, and increased ventilator effort contribute to insomnia in patients with COPD.37
Strengths and limitations
The strengths of the current study are that it is population based, is a large study cohort with a wide age span, and includes both sexes, although it is limited to the Swedish population. Furthermore, there was a relatively high response rate, and many relevant confounders have been taken into account.
There are some limitations that should be considered when interpreting the results, however. The use of self-reported questionnaire data can lead to recall bias and the risk of misclassification. The use of self-reported symptoms of insomnia is on par with current insomnia guidelines;5 however, since only the frequency of symptoms and not the duration or daytime consequences were reported, the term “insomnia symptoms” and not “insomnia disorder” was used here. For snoring, there is no “gold standard” for an objective measurement and questionnaires are often used in epidemiological studies. However, even though self-reported snoring has previously been found to correlate well with snoring measured with a microphone,38 the reliability of self-reported snoring remains a problem. Polysomnography was not performed, and the questionnaire did not include questions on common OSA symptoms (eg, witnessed apneas, gasping), which makes it difficult to distinguish those with snoring from those with snoring as a part of OSA. Snoring is the reason patients seek medical assistance from primary care, and most patients with snoring do not have OSA. Therefore, we believe it is of clinical relevance to consider snoring per se as a symptom of interest, especially if we consider snoring as a part of the SDB continuum. Another limitation is the lack of information on previous OSA and/or insomnia diagnosis and continuous positive airway pressure treatment. We have no information on sleep time, as polysomnography was not performed; thus, sleep time could interfere with daytime sleepiness. Information regarding anxiety and depression was not available and could have a potential impact on the results, as it has been found that the risk of mood disorders is higher in those with the combination of snoring and sleep problems.17
Reporting sleepiness ≥ 3 times per week in the Basic Nordic Sleep Questionnaire correlates better with sleep-related symptoms (restless legs syndrome, nocturnal gastroesophageal reflux (nGER) , and insomnia symptoms) and quality of life than the widely used Epworth Sleepiness Scale.39
Although no objective measure of hypertension was included in the current study, the prevalence of hypertension in this study is in line with the prevalence in other studies of the Swedish population.40 For asthma, the prevalence in this study is also in line with previous Swedish studies.41 With regard to COPD, we found a considerably lower prevalence than in studies using spirometry-defined COPD, which may partly be explained by the age distribution in this study (50% aged < 40 years). Furthermore, the definition of COPD as patient-reported physician-diagnosed COPD and/or current medication for COPD does not reflect the true prevalence of COPD, as many who fulfill the spirometry criteria for COPD remain undiagnosed.42
CONCLUSIONS
Participants with snoring and insomnia combined run an increased risk of hypertension, COPD, asthma, daytime sleepiness, and use of hypnotics. The findings in this study are novel and of clinical interest as snoring and insomnia symptoms are very common complaints regarding sleep in the general population and are also a common reason for seeking medical attention. We conclude that it is important to consider the occurrence of snoring in participants seeking medical assistance for insomnia and, vice versa, in patients with snoring inquiring about insomnia.
DISCLOSURE STATEMENT
All authors have seen and approved the manuscript. Work for this study was performed at the Department of Medical Sciences, Respiratory, Allergy, and Sleep Research, Uppsala University, Sweden. Shadi Amid Hägg had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. The GA2LEN study was supported by the EU Framework program for research (contract number FOOD‐CT‐2004‐506378). The current study was also supported by grants from the Bror Hjerpstedt Foundation Uppsala Läns Förening mot hjärt-och kärlsjukdomar and the Swedish Heart-Lung Foundation. The authors report no conflicts of interest.
ACKNOWLEDGMENTS
Author contributions: All of the authors have made substantial contributions to the study design, data collection, and interpretation of results. Shadi Amid Hägg and Elena Ilieva performed the data analysis and wrote the first manuscript draft. All the authors contributed substantially to revising the article critically for important intellectual content and approving a final version before consideration for publication.
ABBREVIATIONS
- BMI
body mass index
- CI
confidence interval
- COPD
chronic obstructive pulmonary disease
- OR
odds ratio
- OSA
obstructive sleep apnea
- SDB
sleep-disordered breathing
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