1. Background
Mean body mass index (BMI) and the prevalence of obesity in children and adolescents increased dramatically from 1975 to 2016 [
1]. Added sugars, particularly in the form of sugar-sweetened beverages (SSB), contribute to excess calories, and may play a role in the development of obesity, because sugars in liquid form may induce less satiety than in solid form [
2] and promote the over-consumption of calories. Health organizations, including the World Health Organization (WHO) and the American Heart Association, have recommended restricting SSB intake to address the obesity epidemic [
3,
4]. Meta-analyses of observational studies mainly from Western settings have suggested higher risk of weight gain or becoming overweight or obese among children with higher intake of SSBs [
5,
6]. However, observational studies are susceptible to unmeasured confounding by socioeconomic position (SEP), unhealthy lifestyle, and health status, making the interpretation uncertain [
7]. Meta-analyses of observational studies not corrected for multiple testing or multiple modeling may be biased and unreliable [
8]. A few randomized controlled trials (RCT) have been conducted in children [
9,
10], which suggested reducing SSB intake reduces weight. However, meta-analyses of RCTs have revealed mixed findings. One meta-analysis showed no overall effect of SSB intake on weight in children, possibly due to low compliance in some included trials [
6]. This meta-analysis also found weight decrease for reduced sugars intake and weight increase for increased sugars intake in trials of adults with ad libitum diets [
6]. However, some others showed small effects of SSB intake on weight or BMI, which may be more marked for increasing consumption of SSB on weight gain and among the overweight [
5,
11,
12]. As a beverage containing naturally occurring sugars, 100% fruit juice was not associated with weight gain in children aged 7 to 18 years in a meta-analysis of observational studies [
13], but no RCT to date has tested the effect of 100% fruit juice on adiposity in children.
Given the inconclusive evidence concerning the effect of SSB on adiposity, assessing the association in settings with different confounding patterns can be helpful [
14]. Unlike in Western developed settings, obesity is less clearly socially patterned in Hong Kong Chinese children [
15,
16]. Chinese children also consume fewer SSBs than those in Western developed countries [
17]. SSB consumption in Chinese children may have different socioeconomic patterns than in Western settings, where children of lower SEP tend to consume more SSB [
18]. Here, we examined the association of SSB frequency at 11 and 13 years with subsequent BMI z-score and overweight (including obesity) up to 18 years and waist circumference (WC), waist-to-hip ratio (WHR) and body fat percentage (BFP) at 16 to 19 years in the non-Western developed setting of Hong Kong using a large, population-representative Hong Kong Chinese birth cohort “Children of 1997”.
3. Results
Of the 8327 individuals originally recruited to the “Children of 1997” birth cohort, as of December 2018, 28 had permanently withdrawn. Of the remaining 8299, 7934 were potentially contactable for Survey I in 2008–2009, whilst 75 migrated without trace, 12 deceased, and 278 were untraceable (probably migrated or dead). Of these 7934, 3678 responded to Survey I, of whom 98.6% provided information on SSB consumption at about 11 years (mean age at assessment 11.5 ± 0.3 years) (
Figure S1). The proportion of English responses was very low (7/3678 = 0.2%). The 3628 children with information on SSB consumption and 4670 children without were significantly different relating to some characteristics, but the magnitude of the difference was small for sex, maternal age at birth, mother’s place of birth, highest parental education, highest parental occupation, and household income per head (all Cohen effect sizes <0.1) [
25] (
Table S1). At about 11 years, 33.1% had not consumed SSB during the past week, 50.7% consumed 1–3 times during the past week, 9.4% consumed 4–6 times, and 6.8% consumed daily. The mean of BMI at 11 years was 18.55 ± 3.24 kg/m
2 and BMI z-score was 0.21 ± 1.27.
Table 1 shows that boys, those with younger mothers, mothers born in Hong Kong, or those had ≥1 h/day of physical activity, less frequent fruit and vegetable consumption, and more frequent meat consumption were more likely to consume SSB. SSB consumption was not related to SEP (parental education, parental occupation, and household income).
Table 2 shows that SSB consumption was neither associated with BMI z-score nor overweight (including obesity) from 12 to 18 years in all four models using MI/IPW. Repeating the analysis using a complete case analysis or using BMI z-score or centile based on the 2012 IOTF reference [
24] in a complete case analysis produced similar results (
Table S2). There were no clear dose-response associations of SSB consumption with WC, WHR or BFP at 16–19 years in all four models using MI/IPW (
Table 3) or complete case analysis (
Table S3). After considering potential under-reporting of SSB frequency, we found that a positive association of 1–3 times per week of SSB consumption with overweight was possible if 20% or a larger proportion of 1–3 times per week were underreported as less than weekly, or 15% or more of 1–3 times per week, 4–6 times per week and daily were underreported as a lower frequency category (
Table S4). We also found no association of SSB consumption frequency at 13 years with measures of adiposity in a complete case analysis (
Table 4). Using a composite measure of SSB intake at 11 and 13 years gave a similar interpretation (
Table S5).
4. Discussion
In this large, population-representative birth cohort of Hong Kong Chinese children, SSB frequency at 11 or 13 years was not associated with subsequent BMI z-score or overweight (including obesity) up to 18 years, nor with WC, WHR or BFP at 16–19 years.
To our knowledge, this is the first study to examine the association of SSB consumption with adiposity using a prospective cohort of Chinese children. Cross-sectional studies in Chinese children [
17,
28] have shown a positive association of regular SSB consumption with obesity and abdominal obesity in 6–13-year-olds [
28] and an association of SSB consumption with abdominal but not general obesity in 6–17-year-olds [
17]. Our lack of association of SSB consumption frequency with subsequent BMI z-score or other measures of adiposity differs from an observational study [
29] and meta-analyses of observational studies largely from Western settings [
5,
6,
30,
31]. A cohort study conducted in US children suggested that BMI z-score was 0.050 higher (95% CI 0.022 to 0.079) for each additional 8 oz/day of SSB consumed at ages 2 to 17 years [
29]. The discrepancy between our study and that of Marshall et al. [
29] may be because the participants in our study had a much lower SSB intake (6.8% consumed SSB daily at 11 years) than those in that study (median 8 oz/day at 11 years). Notably, Marshall et al. also found a positive association of water/sugar-free beverages with BMI z scores [
29], thus confounding may exist. In the US, both SSB intake and adiposity are strongly associated with socio-economic position, which could confound the estimates [
15,
16]. The social patterning of SSB consumption and of obesity is less marked in our Hong Kong Chinese setting [
15], making our observations less open to confounding. Our finding of no association of SSB frequency with subsequent BMI z-score is inconsistent with two RCTs in children, showing that reducing SSB intake reduces weight [
9,
10]. A possible explanation is that subjects in the two trials had high daily SSB intake at baseline, thus the findings may not apply to individuals with a low SSB intake. Our finding of little association of SSB consumption frequency with adiposity is more consistent with the limited evidence from meta-analyses of RCTs of SSB showing minor effects on obesity [
5,
6,
11,
12] which are more pronounced in overweight individuals.
SSB is the largest source of added sugars in US children [
32], although the contribution of SSB to added sugars intake has declined and is no longer the largest source in some countries, such as the Germany [
33]. SSB may contribute to obesity because sugar in liquid form adds to calories but induces less satiety than in solid form and may weaken any compensatory reduction in subsequent calorie intake and facilitate over-consumption of calories [
2]. However, a recent experimental study in mice found no difference in adiposity by sucrose intake but did find differences by fat intake [
34], suggesting that fat rather than sucrose drives over-consumption. Observationally, consumption of 100% fruit juice, which may contain as much sucrose as SSB, is unrelated to weight gain in children aged 7–18 years despite slight weight gain in younger children, although this observation has not been confirmed in an RCT [
13]. Instead, the observed association of SSB with adiposity in Western populations could be due to modern patterns of sugary/fatty snacking characterized by high SSB consumption, rather to sugar itself [
35].
Despite being conducted in a setting where diet has been reported quite accurately in terms of total calories [
36], and confounding may be less marked [
15], our study has several limitations. First, SSB consumption was obtained by a food frequency questionnaire and may be underreported due to social desirability bias [
37]. Non-differential misclassification of SSB frequency usually biases towards the null, which could have obscured a positive association of SSB with overweight if ≥20% of those drinking SSB 1–3 times/week underreported as less than weekly, or ≥15% of those drinking SSB 1–3 times/week, 4–6 times/week and daily were underreported as a lower category. Baseline SSB consumption may subsequently change. However, we found no association of SSB consumption frequency at 13 years with adiposity. Second, we have no information on total energy intake or amount of SSB intake, because we did not collect comprehensive detailed dietary information but only food frequency information. We have no information on the consumption of specific types of SSB, thus the reported SSB may include beverages sweetened with sugar or non-nutritive sweeteners. We assessed only canned SSB, which may have excluded those in bottles or cups and lead to the underreporting of SSB intake. Third, hydration status was not controlled for in the measurement of BFP. However, BFP was measured in the morning in healthy participants after an overnight fast, which likely reduces measurement error due to hydration status, illness, alcohol use or intense exercise. Fourth, only about 40% of the cohort were included, so selection bias is possible. However, those included and excluded were similar and we used IPW to recover the original sample. Fifth, variability in measures of adiposity was limited and few were obese (~4%), potentially reducing power. We only have 80% power to detect an effect size of 0.09 or greater in BMI z-score (i.e., BMI increase of 0.3 kg/m
2 or greater) for 1–3 times or more per week as compared to less than weekly, thus we cannot exclude a small effect of SSB on adiposity [
5,
30], or an effect of SSB for overweight and obese children.
SSB consumption is seen as an important target of intervention to combat obesity in Western countries. However, added sugars and SSB intake have declined while obesity has risen steeply over the same time period in Australia, which to some extent challenges the assumption that reduced consumption of SSB can, in itself, help reverse the upward trend of obesity [
38]. SSB consumption, as a marker of an unhealthy lifestyle characterized by more energy intake, less exercise, and a poor dietary pattern [
39], alone may not dramatically contribute to obesity over time, but rather a constellation of structural, environmental and personal factors that impact long-term weight gain. Still, the overconsumption of SSB remains an important risk factor for the development of obesity in Western children with high SSB intake and strategies targeting SSB as a source of excess energy appear to be prudent [
39]. Better understanding of the role of SSB intake in obesity in different populations would ensure policy initiatives are invested in effective targets of intervention.