Is obesity associated with early sexual maturation? A comparison of the association in American boys versus girls.

BACKGROUND: Increasing evidence suggests a close association between early sexual maturation (SM) and obesity in girls and female adults. Earlier maturing girls are more likely to be obese than nonearly maturers. However, limited research has been conducted in boys.
OBJECTIVE: To examine the influence of early SM on fatness in boys and compare it with girls, and to test the hypothesis that the associations differ by gender because of the differences in growth and SM patterns in boys and girls. STUDY
DESIGN: Cross-sectional study.
SUBJECTS: One thousand five hundred one girls and 1520 boys (aged 8-14 years) who participated in the Third National Health and Nutrition Examination Survey survey (1988-1994) and had complete anthropometry (weight, height, skinfold thickness) and SM data.
METHODS: Based on each individual's age and SM status (Tanner stages: genitalia stages for boys and breast stages for girls), the subjects were classified as: 1) early maturers (those who reached a certain Tanner stage earlier than the median age for that stage), and 2) the others (average and later maturers). Overweight was defined as a body mass index (BMI) > or =85th percentile, and obesity > or =95th percentile. Logistic regression analysis was to test how early maturation affected the risks for overweight and obese. Using multiple linear regression models, the associations between fatness (BMI and skinfold thickness) and SM were systematically examined. Covariates including age, ethnicity, residence, family income, energy intake, and physical activity were adjusted.
RESULTS: Early SM was positively associated with overweight and obesity in girls, but the associations were reverse for boys. The prevalence of overweight in early maturers versus the others was 22.6% versus 31.6% in boys and 34.4% versus 23.2% in girls; the figures for obesity were 6.7% versus 14.8% and 15.6% versus 8.1%, respectively. Odd ratios and 95% confidence intervals for obesity were 0.4 (0.2, 0.8) for boys and 2.0 (1.1, 3.5) for girls, and covariates were adjusted. Most significant differences in overweight and obesity among ethnic groups disappeared after controlling for SM. Fatness (BMI and skinfold thickness) was associated with SM stages and with early maturation in boys and girls, but the associations were in opposite directions. Compared with their counterparts, early maturing boys were thinner, whereas early maturing girls were fatter.
CONCLUSIONS: Obesity is associated with sexual maturation in both boys and girls, but the association differs. There is positive association in girls, but a negative one in boys. Maturation status should be taken into consideration when assessing child and adolescent obesity.