Exploring reasons for a puzzling developmental difference between the sexes.
Reprinted from Eating Disorders Review
July/August 2010 Volume 21, Number 4
©2010 Gürze Books
Unlike overweight girls, who tend to reach puberty earlier than do girls of normal weight, overweight and obese boys in the U.S. may begin puberty later than thinner boys. These findings came from a study by Joyce M. Lee, MD, MPH and colleagues at the University of Michigan (Arch Pediatr Adolesc Med. 2010; 164:139).
At 11.5 years of age, boys with the highest body mass index (mean BMI z score 1.84) were 165% more likely to be prepubertal than were the thinnest boys, according to Dr. Lee and her colleagues. In one of the first longitudinal studies of weight and timing of puberty in males, the study results showed that unlike girls, higher body mass index, or BMI (kg/m2) in earlier childhood may be associated with and may precede later onset of puberty among boys. To further explore the relationship, Lee and colleagues analyzed the records of 401 boys from diverse socioeconomic backgrounds in 10 regions of the U.S. The authors used data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development, which included data from full-term single children born in 1991.
The data included height and weight measurements of the children from age 2 years to 12 years, along with a visual assessment of whether the children had begun puberty by the age of 12, using Tanner genitalia staging at 9.5, 10.5, and 11.5 years. Boys were defined as pubertal if they were at Tanner stage 1 at 11.5 years and were otherwise categorized as pubertal.
For children and teens, overweight is defined as BMI at the 85th to 95th percentile and obesity as BMI greater than the 95th percentile, using Centers for Disease Control and Prevention BMI-for -age growth charts. Using these criteria, 14.4% of the teens were found to be overweight and 19.4% were obese by age 11.5. Overall, 49 boys, or 12.2%, were prepubertal at age 11.5, using Tanner staging.
The authors feel that their findings have important implications for understanding gender-based differences in the physiological mechanisms of puberty. Since puberty is regulated by the gonadotropin-releasing hormone axis for both girls and boys, it is not clear why such different associations between body fat and the timing of the onset of puberty would exist between the sexes.
The study did have some limitations, such as an inability to analyze the data according to race; most of the children in the study were Caucasian and the relationship between body fat and BMI is affected by race. In light of the increase in childhood obesity, the authors note that additional studies are needed to further investigate the epidemiologic link between body fat and the start and progression of puberty among boys.