A new analysis of a major study of childhood nutrition shows that early sexually-maturing girls are more likely than other girls to be obese, while in boys early developers are less likely to be obese than other males. The analysis, by University of Illinois at Chicago nutritional epidemiologist Dr. Youfa Wang, appears in the November issue of the journal Pediatrics. Although previous studies have suggested that sexual maturity is associated with obesity in females, little was known about the relationship in boys until now. The finding of a reverse association between sexual maturity and obesity in boys sheds new light upon this issue, providing additional evidence for the influence of sexual maturity on fatness.
According to Wang, who is assistant professor of human nutrition at UIC, the gender differences observed in the association between sexual maturity and obesity are likely related to differences in biological development. In boys, for example, early developers were found to be significantly taller, but not heavier, than their average- or late-maturing counterparts. By comparison, early sexual maturity in girls was associated with both increased height and weight.
"This suggests that sexual maturity might have different biological influences on growth in weight and height in boys and girls," Wang said. "During the growth process in boys, more energy may be devoted toward height than to the development of fat tissue, while early-maturing girls are more likely to store extra energy intake as fat tissue."
The new study looked at childhood obesity by assessing body stature and early sexual maturation among 1,501 boys and 1,520 girls ages 8 to 14 who participated in the Third National Health and Nutrition Examination Survey from 1988 to 1994, conducted by the U.S. Centers for Disease Control and Prevention. Younger and older children from that study were not considered in Wang's analysis.
Wang classified the children as "early maturers" if they reached a certain stage of sexual development earlier than their peers in the study. To examine the association between sexual maturation and obesity, adjustments were made for age, ethnicity, residence, family income, diet and physical activity.
The new study suggests the need for further investigation into the causal relationship between the timing of sexual maturation and development of obesity as well as the influence of behavioral, social and environmental factors on gender differences, Wang said. His study, he noted, is based on cross-sectional data and cannot test causality.
In a wealthy society like the United States, attitudes and expectations toward body weight are different for females and males, Wang notes. Thinness is considered desirable and attractive for females; bigness and full musculature are considered attractive for males. According to Wang, these factors may contribute to differences in adolescents' eating behaviors, body images, and exercise patterns, all of which might play a role in the association between sexual maturation and obesity.
The World Health Organization has identified the increase of obesity in children and adolescents as a major public health concern in the United States and worldwide, and Wang says further understanding of the relationship between sexual maturity and obesity has important clinical implications.
"It can help refine and develop appropriate measurement references," he said. "And it can help guide us in employing more effective methods and resources used in preventing and managing childhood and adolescent obesity."
