Sodium and potassium urinary excretion levels of preschool children: Individual, daily, and seasonal differences

Abstract

In this study, the authors measured sodium and potassium concentrations in spot urine samples of preschool children on multiple days, and evaluated individual, daily, and seasonal effects. A total of 104 healthy preschool children aged 4 to 5 years were studied. Urine samples were collected from the first urine of the day after waking for three consecutive days (Monday–Wednesday) four times a year (spring, summer, autumn, winter). The authors estimated the daily urine volume as 500 mL and daily creatinine excretion as 300 mg, and used these to calculate daily sodium and potassium excretion levels. Daily sodium and potassium excretion levels and sodium to potassium ratios were highly variable. The coefficient variant in the children's excretion levels were also high within and between individuals. Sodium excretion levels and sodium to potassium ratios were higher on Monday (weekend sodium intakes) than Tuesday. Season had no effect on sodium or potassium excretion levels, but the sodium to potassium ratio was higher in summer than in winter. In conclusion, levels of urinary sodium excretion are comparatively high and those of potassium are low in preschool students, with high variability within and between individuals.

1. INTRODUCTION

Hypertension has become increasingly prevalent in developed countries, and early prevention by moderating the sodium and potassium intakes of infants and preschool children has gained awareness.1, 2 In a double‐blind randomized trial of 476 newborn infants assigned to either a low‐sodium or normal‐sodium diet, the infants with a low‐sodium diet showed lower systolic blood pressure (BP) than infants with a normal‐sodium diet.3 This effect was reported to persist in the infants with a low‐sodium diet 15 years later.4 Rangan and colleagues5 assigned 335 patients at 18 months of age to four groups according to their intake levels of sodium and potassium, and checked their systolic BP levels at 8 years old. They found that higher sodium intakes correlated with higher systolic BP, and higher potassium intakes correlated with lower systolic BP. These studies have led to implications of high‐sodium and low‐potassium intakes from early stages of childhood as important risk factors for hypertension. To moderate the levels of sodium and potassium intake from an early age, it is necessary to accurately determine the prevailing intake levels of young children.

It has been reported by the National Health and Nutrition Examination Survey (NHANES) that in American children aged 4 to 5 years, the average sodium intake is 109 mmol/d (salt: 6.4 g/d) and potassium intake is 53 mmol/d.6 The Japanese National Health and Nutrition Survey reports that in Japanese children aged 1 to 6 years, the average sodium intake for boys is 100 mmol/d (salt: 5.9 g/d) and for girls is 88 mmol/d (salt: 5.4 g/d).7, 8 Sodium and potassium intakes are often estimated by measuring urinary concentrations. In a study of 79 children aged 3 to 5 years, Haga and colleagues9 used a 24‐hour urine collection method and reported that the urinary sodium excretion level was 79 mmol/d (salt: 4.6 g/d). Morinaga and colleagues10 estimated the urinary sodium excretion of 1424 children aged 3 years using spot urine samples, and reported the mean value as 75 mmol/d (salt: 4.4 g/d). However, these results for sodium intake and excretion are from 1‐ to 2‐day studies, which may not reflect the average intake/excretion levels of sodium and potassium because these fluctuate within and between children.11, 12 Moreover, because sodium intake/excretion may fluctuate daily (between week and weekend days) and/or by season, we believe the details of sodium intake/excretion of preschool children are yet to be well defined. Likewise, the precise potassium intake levels of preschool children are also unknown. Thus, the aims of this study were first to estimate the sodium and potassium excretion levels in preschool children by measuring their concentrations in spot urine samples and second to evaluate individual, daily, and seasonal variability in sodium and potassium excretion levels.

2. METHODS

2.1. Study population

Our target population included healthy preschool children aged 4 to 5 years attending Tensho Kindergarten in Koga city, Fukuoka Prefecture, Japan. A briefing session was held for the parents of the 119 preschool children in April 2015, and the parents of 107 children agreed to participate in the study. Of these children, 104 (53 boys, 51 girls) completed the study (three withdrew by agreement) (Figure 1).

Figure 1.

Consolidated standards of reporting trial flow diagram of the study participants

2.2. Intervention schedule

We asked the children's parents to collect part of the first urine passed after morning waking in the provided bottle on 3 consecutive days (Monday, Tuesday, and Wednesday) during each designated period. The urine samples were brought to kindergarten on the day of collection and preserved at low temperature. This was performed in spring (April–May), summer (June–July), autumn (November), and winter (February) during 2015–2016. Because urinary sodium excretion tends to reflect sodium intake of the day before,13, 14 we considered the samples collected on Monday to indicate weekend intake (no kindergarten), and those collected on Tuesday and Wednesday to indicate weekday intake. It should be noted that all the target children took the same school lunch on weekdays. We informed the parents of the estimated urinary sodium and potassium excretion levels of their children after completion of the study.

2.2.1. Anthropoid measurements

Body height and weight of the target children were measured in April and September of 2015 and the mean value was used in this study. The Kaup index of the target children was calculated (Kaup index = weight (kg) ÷ height (cm)²×10⁴), and the mean value was confirmed to be within normal range (15–19 g/cm²).

2.3. Estimation of daily urinary excretion levels from spot urine samples

Sodium, potassium, and creatinine concentrations in the spot urine samples were analyzed by SRL, Inc. (Tokyo, Japan), creatinine by an enzyme method, and sodium and potassium by an electrode method. We estimated the daily urine volume of the children to be 500 mL. This value was derived from a study of Japanese children of similar age (3–5 years) and mean weight (17.4 kg) that measured the daily urine volume as 533±185 mL (31±12 mL/kg).15 We then calculated daily sodium and potassium excretion levels as a proportion of daily creatinine excretion. This was performed following Morinaga and colleagues,10 who calculated daily sodium and potassium excretion levels per 300 mg/d creatinine excretion, estimated from the urine creatinine concentration and urine volume of their study population of 1424 three‐year‐old Japanese children. As in previous studies, we estimated the creatinine excretion of the children in the present study to be 300 mg/d and the estimated urine volume to be 500 mL. The coefficient of variation (CV) of urinary excretion was calculated as CV=standard deviation÷mean value×100.

2.4. Recommended sodium and potassium intake levels for preschool children

The World Health Organization (WHO) guidelines recommend that the sodium intake for children should be the recommended adult intake of no more than 87 mmol/d (salt: 5.0 g/d) corrected for sex‐specific energy levels. Thus, the WHO‐recommended sodium intake for Japanese preschool children may be calculated using the following equation1, 16:

$$\mathrm{Na}\mathrm{DGx}=87\times (\mathrm{EERx}/\mathrm{EERo})[\mathrm{g}/\mathrm{d}],$$

where Na DGx is the dietary guideline sodium intake (g/d) for boys or girls, EERx is the estimated energy requirement (kcal/d) of the children, and EERo is the estimated energy requirement of adults aged 18 to 29 years (kcal/d); as follows:

$$\begin{array}{c}\hfill \mathrm{Na}\mathrm{DG}(\mathrm{boys})=87\mathrm{mmol}/\mathrm{d}\times (1300\mathrm{kcal}/\mathrm{d}÷2650\mathrm{kcal}/\mathrm{d})\\ \hfill =42.7\mathrm{mmol}/\mathrm{d}(\mathrm{salt}:2.5\mathrm{g}/\mathrm{d}).\end{array}$$

$$\begin{array}{c}\hfill \mathrm{Na}\mathrm{DG}(\mathrm{girls})=87\mathrm{mmol}/\mathrm{d}\times (1250\mathrm{kcal}/\mathrm{d}÷1950\mathrm{kcal}/\mathrm{d})\\ \hfill =55.8\mathrm{mmol}/\mathrm{d}(\mathrm{salt}:3.2\mathrm{g}/\mathrm{d}).\end{array}$$

For practical reasons, Japanese dietary reference intake recommendations are calculated using the WHO‐recommended value, and the reported median value of sodium intake of preschool children from the Japanese National Health and Nutrition Survey of 100 mmol/d (salt: 5.9 g/d) for boys and 94 mmol/d (salt: 5.4 g/d) for girls7, 8 using the following equation16:

$$\mathrm{Na}\mathrm{DGx}=(87\times (\mathrm{EERx}/\mathrm{EERo})+\mathrm{lx}[\mathrm{g}/\mathrm{d}])÷2$$

where Na DGx is the dietary guideline sodium intake (g/d) for boys or girls, EERx is the estimated energy requirement (kcal/d) of the children, EERo is the estimated energy requirement of adults aged 18 to 29 years (kcal/d), and lx is the average value of sodium intake (g/d) for boys or girls reported by the National Health and Nutrition Survey in 2010 and 2011; as follows:

$$\begin{array}{c}\hfill \mathrm{Na}\mathrm{DG}(\mathrm{boys})=[87\mathrm{mmol}/\mathrm{d}\times (1300\mathrm{kcal}/\mathrm{d}÷2650\mathrm{kcal}/\mathrm{d})+100\mathrm{mmol}/\mathrm{d}]\\ \hfill ÷2=71.3\mathrm{mmol}/\mathrm{d}\approx 70\mathrm{mmol}/\mathrm{d}(\mathrm{salt}:4.0\mathrm{g}/\mathrm{d}).\end{array}$$

$$\begin{array}{c}\hfill \mathrm{Na}\mathrm{DG}(\mathrm{girls})=[87\mathrm{mmol}/\mathrm{d}\times (1250\mathrm{kcal}/\mathrm{d}÷1950\mathrm{kcal}/\mathrm{d})+94\mathrm{mmol}/\mathrm{d}]\\ \hfill ÷2=75\mathrm{mmol}/\mathrm{d}\approx 77\mathrm{mmol}/\mathrm{d}(\mathrm{salt}:4.5\mathrm{g}/\mathrm{d}).\end{array}$$

For potassium, WHO guidelines likewise recommend that the intake of children should be the recommended adult intake of at least 90 mmol/d, corrected for sex‐specific energy levels. Thus, the WHO‐recommended potassium intake for Japanese preschool children can be calculated using the following equation2, 16:

$$\mathrm{K}\mathrm{DGx}=90\times (\mathrm{EERx}/\mathrm{EERo})[\mathrm{g}/\mathrm{d}];$$

where K DGx is the dietary guideline intake (g/d) for boys or girls, EERx is the estimated energy requirement (kcal/d) of the children, and EERo is the estimated energy requirement of adults aged 18 to 29 years (kcal/d); as follows:

$$\mathrm{K}\mathrm{DG}(\mathrm{boys})=90\mathrm{mmol}/\mathrm{d}\times (1300\mathrm{kcal}/\mathrm{d}÷2650\mathrm{kcal}/\mathrm{d})=44\mathrm{mmol}/\mathrm{d}.$$

$$\mathrm{K}\mathrm{DG}(\mathrm{girls})=90\mathrm{mmol}/\mathrm{d}\times (1250\mathrm{kcal}/\mathrm{d}÷1950\mathrm{kcal}/\mathrm{d})=58\mathrm{mmol}/\mathrm{d}.$$

There are few reports of quantitative analyses of the association between potassium intake and prevention of lifestyle diseases in Japanese children, so it is difficult to set a recommended potassium intake level for Japanese dietary reference intakes.16 Thus, we decided for this study not to refer to potassium intake levels from the Japanese dietary reference intakes.

To evaluate adherence to the recommended sodium and potassium intakes using the urinary excretion levels of the children, we calculated intake levels by dividing the estimated sodium excretion levels by 0.86 and potassium levels by 0.77, according to Asakura and colleagues.17, 18, 19 It should be noted that, although this conversion factor is for adults, we assumed the urinary sodium and potassium excretion and sodium and potassium intakes of the children were equivalent to adults.

2.5. Ethics

The present study was approved by the ethics committee of Nakamura Gakuen University (approval No. Rinri‐14‐013) and performed in accordance with the Helsinki Declaration of 1975 as revised in 1983. The parents of the children who participated gave informed consent by their own free will after we explained that parents of children will not be disadvantaged if they do not agree with the research, do not participate or if they withdraw part way through the study, and that results may be disseminated to the public at meetings and through publication.

2.6. Statistics

Methods for predicting 24‐hour urinary sodium and potassium excretion from spot urine have been established for adults20, 21, 22 but not children. Here, we attempted to evaluate sodium and potassium intake by calculating urinary excretion of sodium and potassium as a function of excreted creatinine, according to previous reports.10 All data from continuous variables are shown as mean±standard deviation. Paired t tests were used for comparisons of two groups. For comparisons of continuous variables such as anthropometric measurements, which influence urinary excretion levels between sexes, we checked for normality using the Shapiro‐Wilk test, and compared sexes using paired t tests. Chi‐square test was used for qualitative variables such as order of birth, number of brothers/sisters, whether living with grandparents, and maternal occupation. For comparisons between three or more groups, such as excretion of sodium or potassium and the sodium to potassium excretion ratio between days or seasons, a one‐way analysis of variance was used and the Tukey‐Kramer post‐hoc test was used where results were significant.

JMP version 12 (SAS Institute, Cary, NC, USA) was used for statistical analyses.

3. RESULTS

The characteristics of the 104 children are shown in Table 1, with no sex differences in these measures. The mean creatinine, sodium, and potassium concentrations of the children's spot urine samples across the 12 days were 90.4±21.5 mg/dL, 136.6±31.3 mmol/L, and 38.7 mmol/L, respectively. The estimated sodium and potassium excretion levels per 300 mg creatinine and the sodium to potassium ratio of the children were 52.0±14.7, 14.6±7.5, and 4.6±1.6 mmol/d, respectively, each with a broad distribution (Figure 2). The sodium and potassium excretion levels per 300 mg creatinine for the boys were 51.9±14.7, 15.8±8.8, and 4.3±1.6 mmol/d, respectively, and for the girls were 52.2±14.9, 13.4±5.7, and 4.8±1.5 mmol/d, respectively, with no differences between the sexes (Table 2). The sodium and potassium daily urinary excretion estimates showed no correlation with order of birth, number of brothers/sisters, whether living together with grandparents, or with maternal occupation. The CVs of the sodium and potassium urinary excretion estimates and the sodium to potassium ratio were higher within than between children (Table 2). A comparison of the daily urinary excretion levels showed higher sodium excretion on Monday (which corresponds to sodium intake on Sunday) than Tuesday, while the potassium excretion level showed no difference between days of the week. The sodium to potassium ratio was higher on Monday (which corresponds to sodium and potassium intake on weekends) than Wednesday (which corresponds to sodium and potassium intake on weekdays) (Table 3). Sodium and potassium excretion levels showed no seasonal effects, while the sodium to potassium ratio was higher in the summer than winter (Table 4). Of the 104 children in our study, 28.8% (n=30) and 1.9% (n=2) met the WHO‐ recommended intake levels of sodium and potassium, respectively, and 80.8% (n=84) met the recommended intake level of sodium according to Japanese dietary reference values (Table 5).

Table 1.

Patient characteristics by sex

	Boys	Girls	Total
No.	53	51	104
Age, y	4.6±0.3	4.5±0.3	4.5±0.3
Height, cm	104.4±4.5	103.5±4.3	103.9±4.5
Weight, kg	17.2±2.2	16.4±1.8	16.5±2.0
Kaup index, g/cm2	15.7±1.3	15.3±1.0	15.5±1.2
No. of brothers and sisters (0/1/2/3)	9/31/12/1	8/30/10/3	17/61/22/4
Order of birth (1/2/3/4)	29/18/6/0	29/15/5/2	58/33/11/2
Living together with grandparents (yes/no)	8/45	7/44	15/89
Occupation of mother (regular/part‐time/unemployed)	11/13/29	7/14/30	18/27/59

Data are expressed as number or mean±standard deviation.

Kaup index = weight (kg) ÷ height (cm)² × 10⁴.

Figure 2.

(A) Distribution of urinary sodium excretion levels. (B) Distribution of urinary potassium excretion levels. (C) Distribution of the values of the sodium to potassium ratio

Table 2.

Results of spot urine analysis by sex

	Boys (n=53)			Girls (n=51)			Total (N=104)
	Mean±SD	CV, %b	CV, %c	Mean±SD	CV, %b	CV, %c	Mean±SD	CV, %b	CV, %c
Cr excretion, mg/L	95.4±19.8			85.3±22.1			90.4±21.5
Sodium excretion, mmol/L	143±30.2			130±31.6			137±31.3
Potassium, mmol/L	43.9±20.5			33.3±10.8			38.7±17.2
Sodium excretion, mmol/d/300 mg Cra	51.9±14.7	48.5	42.4	52.2±14.9	44.3	36.9	52.0±14.7	46.4	40.1
Potassium excretion, mmol/d/300 mg Cra	15.8±8.8	57.2	39.7	13.4±5.7	50.7	37.3	14.6±7.5	54.0	39.0
Sodium to potassium ratio	4.3±1.6	47.2	31.4	4.8±1.5	46.6	31.9	4.6±1.6	46.9	31.5

Abbreviations: Cr, creatinine; CV, coefficient of variation; SD, standard deviation.

^ammol/d/300 mg Cr: calculated using urine volume × urine creatinine concentration.

^bCV (variation within individuals).

^cCV (variation between individuals).

CV of urinary excretion was calculated as CV=SD÷mean value×100.

Table 3.

Comparison of salt and potassium urinary excretion levels between days

	Monday (Corresponds to Sunday Intake Level)	Tuesday (Corresponds to Monday Intake Level)	Wednesday (Corresponds to Tuesday Intake Level)
	Mean±SD	Mean±SD	Mean±SD
Sodium excretion, mmol/d/300 mg Cra	56.0±21.2b	49.8±16.0	50.2±18.1
Potassium excretion, mmol/d/300 mg Cra	14.7±8.9	14.0±7.5	15.1±8.6
Sodium to potassium ratio	4.9±1.8c	4.6±1.8	4.2±1.9

Abbreviations: Cr, creatinine; SD, standard deviation.

^ammol/d/300 mg Cr: calculated using urine volume×urine creatinine concentration.

^b P=0.046 vs Tuesday.

^c P=0.042 vs Wednesday.

Table 4.

Comparison of salt and potassium urinary excretion levels between seasons

	Spring	Summer	Autumn	Winter
	Mean±SD	Mean±SD	Mean±SD	Mean±SD
Sodium excretion, mmol/d/300 mg Cra	53.0±21.5	53.1±18.9	49.6±20.2	52.3±21.3
Potassium excretion, mmol/d/300 mg Cra	15.1±10.8	13.4±7.8	14.3±9.4	15.7±9.4
Sodium to potassium ratio	4.7±2.4	5.0±2.0b	4.6±2.2	4.1±1.5

Abbreviations: Cr, creatinine; SD, standard deviation.

^ammol/d/300 mg Cr: calculated using urine volume×urine creatinine concentration.

^b P=0.006 vs winter.

Table 5.

Adherence to sodium and potassium intake guidelines of WHO and the Japanese dietary reference intakes 2015

	Organization	Recommended Values for Nutrient Intake, mmol/d	Recommended Values Adjusted for Excretion, mmol/da	Probability of Meeting the Recommended Values Adjusted for Excretion, %
				Total	Boys	Girls
Sodium, mmol/d	WHO (boys, girls)	<42.7, <55.8	<36.7, <47.9	28.8	15.1	43.1
	Japanese dietary reference intake (3‐ to 5‐year‐old boys, girls)	<70, <77	<60.2, <66.2	80.8	75.4	86.3
Potassium, mmol/d	WHO (boys, girls)	≥44.2, ≥57.7	≥34.0, ≥44.4	1.9	3.8	0.0
	Japanese dietary reference intake (3‐ to 5‐year‐old boys, girls)	–	–	–	–	–

Abbreviation: WHO, World Health Organization.

^aThese values were divided by 0.86 for sodium and 0.77 for potassium for 0.7726, 27 to apply the recommendations for dietary intake to the excretion data.

4. DISCUSSION

Sodium intakes within and between individuals are known to fluctuate greatly,12 therefore the intake and excretion levels of sodium on a particular day do not always reflect average levels.11 To our knowledge, this is the first study to report the sodium and potassium levels and CVs in spot urine samples collected on multiple days from children. When we analyzed the results of the target children using creatinine excretion as 300 mg/d and estimated urine volume as 500 mL according to previous reports,9, 10 the mean estimated sodium excretion level across the 12 days was 52.0 mmol/d for the children in this study, which was lower than a previous report of the urinary sodium excretion level measured from samples collected on a single day.10 Since the mean body weight of the target population of this study was 16.5 kg, which is heavier than a previous report (3‐year‐old children: mean body weight 13.7 kg),10 the true creatinine excretion level may have been higher than the value we used here (300 mg/d), and consequently may have underestimated the urinary sodium excretion level.

Conversely, the mean potassium level across the 12 days was 14.6 mmol/d, which is lower than that previously reported from a large study,10 and needs verification. The reason may be that sodium and potassium excretion is not constant through the day. Although morning spot is in best correlation with 24‐hour sodium excretion, it is the afternoon spot that correlates better with 24‐hour potassium excretion.23 Additionally, urinary potassium excretion may be underestimated by the same reason as sodium. Nonetheless, future analyses of 24‐hour urinary excretion of a larger population on multiple days must re‐evaluate the results we presented here.

It should be noted that the sodium and potassium intakes showed no sex differences in this study, which is not the case for adults. This probably results from the fact that the differences in stature and dietary intake between the sexes are smaller in children than in adults, evidenced by the anthropometric measurements in this study showing no significant difference (Table 1). Our results show that children generally exceed the sodium intake levels and fall short of potassium intake levels recommended by WHO guidelines dietary reference intakes even if the underestimation is concerned (Tables 2 and 5).1, 2, 6 It is of concern that only about 28.8% of children in this study met the WHO recommendation for sodium, and 1.9% met the WHO recommendation for potassium intake (Table 5). It is well known that adults consume more sodium than other populations19, 24, 25; our study suggests that Japanese children also consume excess sodium. We believe this tendency is not special only for Japanese preschool children but believe that it is found in many other developed countries and must be discussed as a worldwide problem.

The CVs for daily sodium excretion levels within and between children in our study were 46.4% and 40.1%, respectively, which are much higher than those reported for adults (34%–36% and 15%–20%, respectively).12 Similarly, the CVs for daily potassium excretion levels within and between children in our study were 54.0% and 39.0%, respectively, which are also higher than those reported for adults (24%–27% and 17%–24%, respectively) (Table 4).12 Because the CVs within and between individuals were much higher in children than adults, the timing of measurements must be considered when evaluating sodium intake of an individual child, especially as the degree of variation was higher within rather than between children.

When we compared days of the week, the sodium excretion level and sodium to potassium ratio were significantly higher on Monday (which corresponds to sodium and potassium intake on Sunday) than Tuesday and Wednesday, respectively (Table 3). Generally, because the meals on weekends and weekdays differ, the intake levels of energy and energy‐producing nutrients also differ.26, 27 Our results differ from a report where school children aged 6 to 16 years showed weekday/weekend differences in sugar and lipid intake but not in sodium intake, as estimated from a dietary questionnaire (24‐hour recall method).27 However, this can be affected by differences in age, race, and dietary culture of the population under study.

Conversely, we found no seasonal differences in sodium or potassium excretion levels, although the sodium to potassium ratio was higher in the summer than winter (Table 4). This is possibly the result of different dietary menus between seasons. Arakawa and colleagues reported that sodium excretion levels estimated from spot urine samples of Japanese adults with hypertension were significantly lower in summer compared with other seasons,28 suggesting that seasonal fluctuations must be taken into consideration for adults as well as children. Taken together, our results suggest that sodium and potassium urinary excretion levels in children can fluctuate greatly between individuals as well as across days and seasons within an individual.

A relationship between sodium intake and BP has been suggested to exist from infancy.3, 4, 5, 29 Shi and colleagues30 showed that consuming an additional 1 gram of salt per day increased systolic BP by 0.2 mm Hg, in their study of 24‐hour urinary sodium excretion levels and BP in 435 children. The INTERSALT study showed that consumption of an additional 1 gram of salt per day increased systolic BP in adults year by year.24 Additionally, it has been reported that increased sodium intake in childhood increases the risk of obesity and high BP in adulthood.31 These findings suggest that moderating sodium intakes in early childhood improves the chances of having healthy BP in later life. In Japan, the need to reduce salt intake in middle‐aged adults has been promoted to prevent and treat hypertension, but moderating the salt intake of children, including infants, lack recognition of its importance. A meta‐analysis of studies of reduced salt intake in children, including infants, has shown significant attenuation of BP.29 Thus, the findings of our study showing excess salt intake in Japanese preschool children imply that moderation of salt intake from an early age is an important yet to be conducted issue.

STUDY LIMITATIONS

Limitations of this study were threefold. First, the sodium and potassium excretion levels estimated by first urine passed after morning waking is not confirmed by 24‐hour urinary excretion level. Comparison of spot urine and 24‐hour urine collection of children must be performed in future studies. Second, our definition of sodium excretion levels as a proportion of creatinine excretion may underestimate their value in children with high muscle mass and overestimate them in children with low muscle mass. We found no correlation between urine sodium excretion level, body weight, or Kaup index (data not shown). It is possible to correct each sample for body weight, but since we found no specific basis for this, and this correction may complicate the interpretation, we used a single creatinine value for all children, as previously reported. Thus, the true levels of urinary sodium excretion are possibly even more widely distributed. Third, the sources of sodium intake were unknown as we did not conduct a dietary questionnaire during the period of study. Fourth, the scale of the study was small, with results from a single childcare facility. An investigation in a larger population of children from multiple facilities is required.

CONCLUSIONS

Our study shows excessive sodium excretion and low potassium excretion in preschool children, and that sodium and potassium excretion levels of children vary greatly between individuals and across days and seasons within an individual.

CONFLICT OF INTEREST

None of the authors have any conflicts of interest to disclose.

Yasutake K, Nagafuchi M, Izu R, et al. Sodium and potassium urinary excretion levels of preschool children: Individual, daily, and seasonal differences. Journal of Clinical Hypertension. 2017;19:577–583. 10.1111/jch.12966