Severe obesity in children: prevalence, persistence and relation to hypertension

Abstract

Background: Newer approaches for classifying gradations of pediatric obesity by level of body mass index (BMI) percentage above the 95th percentile have recently been recommended in the management and tracking of obese children. Examining the prevalence and persistence of severe obesity using such methods along with the associations with other cardiovascular risk factors such as hypertension is important for characterizing the clinical significance of severe obesity classification methods.

Methods: This retrospective study was conducted in an integrated healthcare delivery system to characterize obesity and obesity severity in children and adolescents by level of body mass index (BMI) percentage above the 95th BMI percentile, to examine tracking of obesity status over 2-3 years, and to examine associations with blood pressure. Moderate obesity was defined by BMI 100-119% of the 95th percentile and severe obesity by BMI ≥120% × 95th percentile. Hypertension was defined by 3 consecutive blood pressures ≥95th percentile (for age, sex and height) on separate days and was examined in association with obesity severity.

Results: Among 117,618 children aged 6-17 years with measured blood pressure and BMI at a well-child visit during 2007-2010, the prevalence of obesity was 17.9% overall and was highest among Hispanics (28.9%) and blacks (20.5%) for boys, and blacks (23.3%) and Hispanics (21.5%) for girls. Severe obesity prevalence was 5.6% overall and was highest in 12-17 year old Hispanic boys (10.6%) and black girls (9.5%). Subsequent BMI obtained 2-3 years later also demonstrated strong tracking of severe obesity. Stratification of BMI by percentage above the 95th BMI percentile was associated with a graded increase in the risk of hypertension, with severe obesity contributing to a 2.7-fold greater odds of hypertension compared to moderate obesity.

Conclusion: Severe obesity was found in 5.6% of this community-based pediatric population, varied by gender and race/ethnicity (highest among Hispanics and blacks) and showed strong evidence for persistence over several years. Increasing gradation of obesity was associated with higher risk for hypertension, with a nearly three-fold increased risk when comparing severe to moderate obesity, underscoring the heightened health risk associated with severe obesity in children and adolescents.

Figure 1

The proportion of children and adolescents with moderate and severe obesity by age, sex and race/ethnicity. Comparisons by race/ethnicity within each age-sex group showed that the prevalence of obesity (BMI ≥95^th percentile) was significantly different between all racial/ethnic subgroups (p < 0.01) except for differences in obesity prevalence for black vs Asian 6–11 year old boys (p = 0.90), black vs. Hispanic 6–11 year old girls (p = 0.64), and white vs. Asian 12–17 year old boys (p = 0.37). The prevalence of severe obesity (BMI ≥120% of the 95^th percentile) was also significantly different between all racial/ethnic subgroups (p < 0.01), except for white vs. Asian (p = 0.06) and black vs. Hispanic 6–11 year old girls (p = 0.96), and white vs. Asian 12–17 year old boys (p = 0.58).

Figure 2

Follow-up BMI category based on BMI percentile and BMI percentage of the 95^th percentile by age and BMI at the index visit. (A) For children with normal BMI at the index visit (N = 50,685), an increasing proportion of younger children were overweight at 2–3 years of follow-up (p < 0.001 comparing 6–7 and 8–9 year olds to 12–13 year olds, with no differences between 10–11 and 12–13 year olds, p = 0.6). (B) For children who were overweight at the index visit (N = 14,057), an increasing proportion of younger children were obese at follow-up (p <0.001, test for trend). (C) For children who were moderately obese at the index visit (BMI 100-119% of the 95^th percentile, N = 9848), an increasing proportion of younger children were obese at follow-up (p <0.001, test for trend). The proportions of moderately obese children who remained obese at follow-up were significantly different between all age groups (p <0.01) except for 10–11 year olds compared to 12–13 year olds. (D) For children who were severely obese at the index visit (N = 4295), nearly all were obese or severely obese at follow-up (95.7-99.3%). Children in the youngest age group (6–7 years old) had the highest prevalence of severe obesity at follow-up compared to other age groups (p <0.05). Differences between the older age groups were not significantly different.