This study examined the prevalence and recent trends of HCB consumption among Korean adolescents. This study also investigated socio-demographic and behavioral factors related to HCB consumption in a nationally representative sample of Korean adolescents. To the best of our knowledge, this is the first study to comprehensively examine HCB consumption using multiple years of KYRBS data.
In this study, boys were more likely to consume HCBs, consistent with findings in previous studies [6, 7]. However, correlates of HCB consumption were generally similar for boys and girls. For both sexes, adolescents who consumed HCB were more likely to be obese, to drink soda at least once a week, and to drink sweetened beverage at least once a week. This not only confirms previous findings that the sugar content and the subsequent sweet flavor are reasons why adolescent consume HCBs [36, 37], but it also suggests that for adolescents consuming HCBs, the sugar content and its subsequent impact on weight may mask any weight-loss effect expected from the caffeine content [23, 26]. Hence, HCB abuse should be considered a concern for obesity as well as caffeine abuse.
Both boys and girls who consumed HCBs were more likely to engage in risky behaviors (alcohol and tobacco use) than nondrinkers, although the effect sizes were negligible. This is generally consistent with previous findings that adolescents with risky behaviors are more likely to consume HCBs [5, 6, 20, 38]. Similarly, adolescents who consumed HCBs were more likely to feel stressed, sad and depressed, feel unrested after sleep, and have suicidal thoughts and suicide attempts. Adolescents who feel stressed and unrested may choose to consume HCB for temporary relief, though it may lead to the development of long-term sleep problems [5, 6, 13, 24].
Some sex differences were observed in the present study. Our regression analyses showed that among boys, HCB drinkers were more likely to have ≥ 20 minutes of vigorous exercise ≥ 3 days per week than nondrinkers. This phenomenon can be explained by how boys are more likely than girls to perceive higher energy and athletic performance after acute administration of caffeine [39]. Because boys perceive higher energy and athletic performance from caffeine [39], they may also expect HCBs to improve their workout, which leads to HCB consumption when engaged in vigorous-intensity exercise. Such association was not observed in girls, as girls were less likely to associate caffeine with athletic performance [39].
Another characteristic unique for boys was how HCB consumption was higher for boys who ate breakfast for low number of days. This may be attributed to how adolescents sometimes consume HCBs as snack supplements when skipping breakfast [40]. However, it is unclear why this phenomenon was observed in boys only. It may be that, in girls, the phenomenon was masked by other characteristics unique to girls, such as maternal education. Our results indicate that girls with mothers having high school education were less likely to consume HCBs than those with mothers having middle school education or less. It may be that mothers who received high school education were aware of potential harms of HCBs, and at the same time, managed intimate mother-daughter relationship. Previous studies have suggested that mother-daughter relationship may be inversely associated with body image and health behavior [41, 42], as mothers with intimate relationship with their daughters are able to function as effective advisors or role models. Similarly, in our study, mothers with intimate relationship with their daughters may have been more effective at discouraging their daughter’s HCB consumption, even when the daughters were tempted to consume HCBs as snack supplements after skipping breakfast. Future strategies to curb HCB use among Korean adolescents should consider such possible sex differences.
The prevalence of HCB consumption was 26.7% for boys and 20.9% for girls in 2017. This is higher than 11.9–14.1% reported in earlier studies [6, 7]. One of our unique findings was the change in prevalence by year, most notable between years 2016 and 2017. We observed a sharp (13.8–23.9%) increase in HCB consumption between years 2016 and 2017, despite Korean government’s policies intended to reduce adolescent’s access to HCBs [17, 18]. This suggests that Korea’s HCB policies may be ineffective, as asserted by a number of critics. For example, one of the existing policies that restrict television advertisements has been criticized for not understanding adolescent’s media consumption, as it only prohibits advertisements between 5–7 pm in which many Korean adolescents are attending Hagwon learning academies and are away from television [43, 44]. A different policy that prohibits the sale of HCBs in school grounds has been criticized for its loopholes, as numerous venues outside school grounds remain free to sell HCBs [44, 45]. Although longitudinal analysis comparing HCB use before and after policy implementation is needed to evaluate the extent of effectiveness of each specific policy, this study shows that overall, existing policies intended to curb adolescent’s HCB use are not as effective as initially envisioned. New strategies are needed to address HCB use, before HCB becomes even more popular among Korean adolescents.
Limitations
This study is not without limitations. First, although efforts were made to include and control for known confounders, there are unmeasured confounders such as the type of HCB, nutrient content of HCB, and access to HCB that could potentially influence the association between independent variables and HCB consumption. Second, this study relied on self-reported data, and given how adolescents have shown to under-report their body weight and over-report their height [46], BMI percentiles computed in this study may have differed slightly from those using direct anthropometric measurements. Third, this study used BMI percentiles to assign weight categories. While BMI percentile is commonly used to predict adiposity in children and adolescents, they cannot account for individuals’ body composition (e.g., amount of fat mass vs. fat-free mass) or fat distribution (e.g., abdominal vs. non-abdominal fat). Lastly, though this study used multiple years of data to best identify factors associated with HCB consumption, this study was not a longitudinal analysis. Numbers reported reflect correlation, but not necessarily causation.