The results of this study revealed increasing trends in the mean values of the external indicators (including BMI, WC, hip circumference, and upper-arm circumference) and 1 internal indicator (lean mass) among the children with a higher frequency of SSBs consumption. For those with a longer nocturnal sleep duration on weekdays, decreasing trends were observed in the mean values of all the internal and external indicators (including bone mass, fat mass, lean mass, and bone density); nocturnal sleep duration on weekends and sleep debt exhibited correlations and related trends with some of the body measurements. After the potential confounders were controlled, and the SSBs consumption variable and the sleep variable were combined, among children with the same frequency of SSBs consumption, lower values of the external indicators and of lean mass were observed in those with a nocturnal sleep duration on weekdays ≥ 9.5 hours, and inverse trends were observed in these values which decreased with increasing sleep duration.
Among the children aged 6–12 years in this study, the average weekend sleep duration was 9.7 hours, and the average weekday sleep duration was 8.8 hours; the findings approximate to the results regarding nocturnal sleep duration obtained through objective measurements in cross-country systematic reviews 36,37. One of the systematic reviews, which complied data on nocturnal sleep duration across 12 countries, reported an average of 8.8 hours (the weighted mean of nocturnal sleep durations on weekdays and weekends)36. Another systematic review, which used actigraphy to compile data from 18 studies, reported an average nocturnal sleep duration on weekdays of 8.7 hours for children aged 6–11 years and of 7.8 hours for children aged 12–14, and an average nocturnal sleep duration on weekends of 8.8 hours for children aged 6–11 years and of 8.5 hours for children aged 12–14 years 37. Although the average nocturnal sleep duration on weekends obtained through this study is longer, it is lower compared with the results of a questionnaire survey conducted in Asia, which reported average nocturnal sleep durations on weekends of boys and girls aged 6–11 years to be 10.1 hours and 10.3 hours, respectively 16. Differences in the number of hours of sleep might vary due to a number of factors, including age, geographical area, and adoption of subjective (questionnaire) or objective measurement (actigraphy). For example, sleep duration decreases with increasing age; the number of hours of sleep in Asia differs from those in other regions; sleep hours of questionnaires completed by parents are larger than those obtained through actual measurement 38,39. In this study, the total nocturnal sleep duration plus the afternoon nap generally satisfies the sleep duration recommended by the American Academy of Sleep Medicine for children aged 6–12 years (9–12 hours) 40.
In this study, the children reported never consuming SSBs only accounted for 7.3% per week, that is, the children consumed SSBs accounted for at least 90% per week. The result differs vastly from those of surveys conducted in other countries, one of which reported an increase prevalence from 47–50% of children aged 6–12 years who did not consume SSBs follow up over six years23, the proportions of the boys and girls aged 10–12 years who did not consume Coca-Cola were 47% and 64.6%, respectively 41. In a study across 12 countries, children aged 9–11 years reported never consuming SSBs throughout the week accounted for 15.1%-75.9% (the percentage varies by SSBs type) 9. In a study on Asian children aged 6–18 years, the proportions of those who did not consume soft drinks and sweetened tea throughout the week accounted for 24.5%-27.7% and 9.9%-11%, respectively 42. These values approximate those in current study, but after deducting the adolescent population in the aforementioned study, the proportion of those who did not consume sweetened tea would be much higher than current study, which highlights the high percentage of SSBs consumption among children in Taiwan.
Numerous systematic reviews have reported correlations between SSBs consumption and obesity, including positive correlations with indicators such as weight, BMI, WC, and body fat 21. Similar associations were observed in the single variable analysis in this study, which, however, disappeared after controlling sleep duration. This was probably due to an effect by the moderation of hours of sleep. Similar results have been reported in a study 43 through a predicted probability plot on overweight or obesity in children aged 10–12 years, showing a higher predictive probability of overweight or obesity in those with a higher level of daily SSBs consumption, particularly in those with a frequency of intake of milk containing added sweeteners (sugar, honey, or chocolate powder) ≥ 4 times per week, with such probability being more marked in those with a sleep duration < 10 hours 43. Additionally, two studies conducted in Asia reported no magnitude of increase in the sleep variable, but after sleep and frequency of SSBs consumption were controlled, higher risk of overweight or obesity was observed in children with a shorter sleep duration and higher frequency of SSBs consumption 44,45. Considering the potential confounder of the aforementioned associations, this study controlled the weight variable, and no correlations were observed in internal indicators, including bone mass, fat mass, lean mass, and bone density, with SSBs consumption. However, numerous children studies have reported an inverse relationship between SSBs consumption and bone health (including bone mass and bone density). Moreover, a few studies have reported a positive relationship between SSBs consumption with fracture 27, including a recent study (2020) which reported higher risk of fracture for those with daily SSBs consumption ≥ 1 serving(s), and the odds ratios for boys and girls were 2.2 (95%CI = 1.0-4.3) and 4.6 (95%CI = 2.3–9.1), respectively 46. Nevertheless, studies on lean mass in adolescents have yielded inconsistent results. A study on adolescents aged 14–18 years reported an inverse relationship between SSBs consumption and skeletal lean mass index 28, whereas a 6-year follow-up study reported no significant associations with lean mass or bone mass but a higher fat mass value in the high SSBs consumption trajectory class 24; in these studies, the sleep variable was not controlled, which prevented from identifying its moderation. Furthermore, associations between SSBs consumption of school children and other indicators of body composition has rarely been investigated, and additional research is required for verification.
Systematic reviews have reported significant negative correlations of sleep with the measurements of obesity, such as weight, BMI, WC, and body fat 17. Current study also verified correlations between children’s nocturnal sleep duration on weekdays and obesity-related indicators. After controlling the SSBs consumption variable, the values of BMI, WC, hip circumference, and upper-arm circumference decreased with increasing sleep duration. The associations are probably due to the variance in the PA level and basal metabolic rate (BMR). Studies have reported a lower PA level ( p < 0.05) as well as higher sugar and energy intake (%) ( p < 0.05) among children with a sleep duration < 7 hours 47; shorter sedentary time ( P = 0.001) and longer duration of light PA ( P = 0.01) per day as well as the BMR value increasing with increasing sleep duration ( P = 0.009 ) in children meeting the recommended sleep duration ≥ 50% of the 7 days of the week 48. However, not all studies showed associations between sleep and obesity indicators. A systematic review revealed inconsistent results, showing that, despite negative correlations between sleep duration and weight of children observed through interventional studies, no associations between sleep duration and BMI were observed through meta-analysis 49. Similarly, although this study reported negative correlations between sleep and some of the measurements of obesity, no correlations were observed with the body fat variable, which was probably due to the moderation of SSBs consumption.
The results of this study revealed that, among children with the same SSBs consumption level, the values of lean mass were lower among those with a longer nocturnal sleep duration on weekdays. Among studies on lean mass, a follow-up study reported an inverse relationship between the sleep duration of children aged 3 years and their fat-free mass index (FFMI; the sum of lean mass and bone mass divided by height [m]²) at the age of four 25. Additionally, a cross-sectional study has reported an inverse relationship between the sleep duration and FFMI among children aged 10–12 years, but this relationship turned positive after controlling sexual maturity 26. For the aforementioned follow-up study, the respondents were younger; the follow-up lasted for one year only, and data on change in sleep and body composition was not provided during the year. Therefore, the effect of sleep on the body reported through the said study have yet to be verified and confirmed through further follow-up studies. Moreover, although the age of the respondents in the aforementioned cross-sectional study were similar to those in current study, that study was structurally based on prepubescent children. Therefore, controlling sexual maturity might be suitable for that study but not exactly for current study. Because half of the respondents in this study were children aged 6–9 years, and pubertal development had not yet begun in this stage, it was unnecessary to control the sexual maturity variable, whereas this variable may be considered in analyzing data on the other half, who were children aged 10–12 years. Additionally, the weight measured through DXA comprised bone mass, fat mass, and lean mass. Studies have reported negative correlations between sleep and weight, but no correlations of sleep with bone mass and fat mass were observed in this study, which probably indicates the crucial role of the correlation between sleep and lean mass. Furthermore, the lean mass measured through DXA involved skeletal muscle and visceral body fat. Further research is required to verify either change in skeletal lean mass or that in visceral body fat affects the increasing/decreasing trends between sleep duration and lean mass.
The strength of this study is its rarity in terms of investigating the correlations between children’s SSBs consumption and sleep with anthropometric assessments or body composition, which facilitates an understanding of the correlations of the aforementioned body measurements related to the health of children. Specifically, the findings of this study revealed negative correlations between sleep duration and lean mass of children. However, this study involved some limitations. First, it was a cross-sectional study, which prevents determination of the causal relationships involved, such as whether frequency of SSBs consumption and sleep duration affected body measurements or physical transformation in children affected SSBs consumption or sleeping habits. Second, the SSBs consumption variable only involved frequency of intake without the amount of intake. According to a systematic review that complied data from 51 countries between 2010 and 2019, the daily SSBs consumption of children ≤ 11 years of age was 303.6 ml 50. By estimation based on the sugar content of Coca-Cola, the daily sugar intake among children approximates 32 grams. Consequently, the calories in the sugar provided through SSBs accounted for 6.7%-7.7% of the total daily energy intake (1666–1908 kcal) of Taiwanese children aged 7–12 years between 2013 and 2016. The percentages approximate 10%, the maximum proportion of free sugars in the daily intake recommended by the WHO, indicating the elevated frequency of daily SSBs consumption among children in Taiwan as well as the attention required to the sugar intake through SSBs. Third, this study did not include sexual maturity as a control variable, which weakened inferential statistics analysis. Because children aged 9–12 years undergo pubertal development, measurements of anthropometric measurement and body composition probably involve marked changes. However, as mentioned previously, this study participants were school children aged 6–12 years, and approximately 50% of them had yet to undergo the stage of sexual development. Meanwhile, this study reduced potential bias in relatively senior children by controlling the age variable. Therefore, the inference of this study is still of great referential value.
Among children with the same frequency of SSBs consumption, nocturnal sleep duration on weekdays was negatively correlated with and exhibited related trends in relation to BMI, WC, hip circumference, upper-arm circumference, and lean mass, which was particularly marked in children with a sleep duration > 9.5 hours compared with those with a sleep duration < 8.5 hours. After the sleep duration variable was controlled, the correlations between frequency of SSBs consumption and body measurements turned nonsignificant, showing the substantial moderation of sleep. Therefore, SSBs consumption and sleep should be considered for children obesity prevention and formulation of relevant public health policies so as to improve the outcomes intended.