Obesity in childhood has been shown to develop into adulthood obesity¹⁾, and hence, it may increase the risk of cardiovascular disease (CVD) later in life2,3,⁴⁾. Moreover, even in youth, obesity is closely associated with high blood pressure (BP)5,⁶⁾ that is known to be an important risk factor for CVD. Thus, the prevention of obesity in childhood may be important in reducing the risk of CVD later in life.

Body mass index (BMI) and waist circumference (WC) are commonly used indices to assess obesity. Most previous studies have reported that BMI and WC are positively correlated with BP in children and adolescents7,8,⁹⁾. Considering that adiposity and fat distribution may be more strongly associated with CVD than simple body mass, and that WC reflects central adiposity, WC can be suggested to be a better indicator of CVD risk such as high BP, than BMI, which reflects both lean and fat mass¹⁰⁾. However, whether WC measured in childhood correlates better with high BP than BMI is still unresolved6,¹¹⁾. In addition, there is little data regarding the correlations of BMI and WC with BP in nonobese and obese adolescents.

In the present study, we examined the associations between BP, BMI, and WC in Korean adolescents using data from the Korean National Health and Nutrition Examination Survey (KNHANES). We analyzed these relationships both in normal weight and overweight groups as well as in all subjects.

An understanding of how hypertension develops in its early stages is important for establishing a strategy for the prevention of CVD. As hypertension is closely associated with obesity in adulthood, we investigated the correlations of BP with obesity indices including BMI and WC in adolescents. The main findings of our study can be summarized as follows. First, both high BMI and high WC were positively correlated with SBP and high SBP in both sexes and DBP and high DBP, in boys. Second, BMI maintained its positive associations with SBP, DBP, high SBP, and high DBP in the normal weight and overweight groups in boys and girls as well as in all subjects of both sexes, even after adjustment for WC. Third, WC lost its positive correlations with SBP, DBP, high SBP, and high DBP in both sexes in the different groups, when adjusted for BMI. To the best of our knowledge, this is the first study to report the independent associations of BMI and WC on BP separately in the normal weight and overweight subsets as well as in all subjects of both genders in adolescents.

Obesity in children and its consequences have been attracting more attention in the medical field because of the increased prevalence of childhood obesity worldwide and the long-term deleterious effects of obesity in adulthood. Furthermore, even early in life, obesity is associated with elevated BP, and persistent childhood hypertension increases the risk for hypertension, CVD, and early death in adulthood¹⁴⁾. BMI and WC are commonly used indices of obesity, and obesity is hypothesized to increase sympathetic nerve activity, insulin resistance, and arterial stiffness, which may thereby elevate BP by increasing cardiac output and vascular resistance¹⁵⁾. Numerous studies have reported positive correlations between high BMI, high WC, and elevated SBP and DBP in children and adolescents7,8,⁹⁾. Our findings are consistent with those studies.

In studies of adults, a central distribution of body fat has been shown to be closely associated with an increase in adverse cardiovascular outcomes¹⁶⁾, and WC has been considered a better indicator of total and abdominal fat mass than BMI. In theory, WC might be more closely associated with cardiovascular risks such as high BP than BMI, which reflects both lean and fat mass. However, this has not been proven in children or adolescents thus far. In the Avon Longitudinal Study of Parents and Children, which compared the magnitudes of the effects of BMI and WC on cardiovascular risk factors, WC was not more strongly associated with BP than BMI⁷⁾. Maximova et al.⁶⁾ reported that WC and BMI had similar effects on changes in SBP in United States children aged 12-13 years. In addition, another study showed that WC was not a better predictor than BMI in identifying children (aged 8-10 years) with high SBP¹¹⁾. In the present study, we observed that BMI was independently and positively correlated with SBP, DBP, high SBP, and high DBP in both sexes when adjusted for WC. In contrast, WC lost its positive associations with SBP, DBP, high SBP, and high DBP in both boys and girls after adjustment for BMI, suggesting that with a given BMI, WC does not seem to influence BP in Korean adolescents.

Another important finding of our study is that BMI was positively associated with SBP, DBP, high SBP, and high DBP in both the normal weight and overweight groups. In some interventional studies, it has been shown that BP substantially decreases when hypertensive or normotensive subjects who are obese lose weight¹⁷⁾. Moreover, in a full range of population-based study in which weight and BP were measured in schoolchildren once between 6 and 15 years of age and again between 15 and 18 years of age, a change in the weight was associated with a change in BP¹⁸⁾. Additionally, the magnitude of change in BP was related to weight gain or loss independently of the initial BP¹⁸⁾. From these results, it can be hypothesized that in adolescents, BMI seems to maintain its positive association with BP at any weight level, and that a change in BMI may lead to a change in BP, irrespective of the individual being initially overweight or hypertensive or not.

In conclusion, BMI correlates better with BP and high BP levels than WC in Korean adolescents. In addition, BMI has a positive association with BP and high BP in the normal weight group as well as in the overweight group.