Obese, overweight boys may face delayed onset of puberty

The growing trend of childhood obesity may be leading to a later onset of puberty among boys, according to a study in the February Archives of Pediatrics and Adolescent Medicine.

Researchers at the University of Michigan found that greater body fat mass in boys tends to delay puberty, while the opposite is true for girls. Past studies showed that girls with a higher BMI reach puberty earlier than normal-weight counterparts.

"It's paradoxical why there's an opposite link in boys and girls," said Joyce Lee, MD, MPH, an author of the study and an assistant professor of pediatrics at the university.

The study cited sex differences in leptin levels during puberty as a possible explanation. While leptin levels continue to rise in girls as they mature, the progression of puberty in boys might require a decrease in levels, which may be blunted among the obese, according to the study.

Regardless, Dr. Lee said, the key is that being overweight and obese impacts children's physical development. "Perhaps doctors can use this as a motivator for parents" to help their children lose weight, she said.

For this study, researchers looked at 401 boys from diverse socioeconomic backgrounds in 10 regions of the U.S. using data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development. The study recruited full-term children born in 1991 and measured their height and weight from ages 2 to 12.

Participants were divided into one of three BMI trajectories -- highest, intermediate and lowest -- based in part on their BMI scores in childhood. Puberty was measured by Tanner genitalia staging. Boys in the first of the five physical development stages, defined as having a lack of genitalia development by age 11.5, were considered to have later onset of puberty.

Overall, researchers found that 12.2% of the 401 participants were prepubertal at age 11.5. Of the 114 boys in the highest BMI group, 14% had a later onset of puberty. Among the 91 boys in the lowest BMI group, 7% had a later onset.

Studies of girls indicate that there are long-term problems associated with later maturation, including an increased risk of breast cancer, according to Dr. Lee. But she said too few studies have been conducted on boys to draw a similar link.

"We need more studies to understand the epidemiological link between body fat and the timing of puberty in boys," Dr. Lee said.