The timing of puberty for boys might be influenced by how much they weigh, a U.S. study suggests.
In an analysis of data from about 4,000 boys ages 6 to 16, researchers found some evidence of delayed puberty for obese youth compared to normal and overweight boys and some evidence of earlier puberty for overweight boys compared with their normal-weight and obese peers.
The results weren't consistent throughout the stages of puberty or across racial groups and the differences in the timing of sexual development weren't always statistically meaningful.
But the findings still matter because they suggest excess weight, which has conclusively been linked to early puberty in girls, may have a different or less linear impact on development for boys, said lead study author Dr. Joyce Lee, a pediatric endocrinologist at Mott Children's Hospital and the University of Michigan in Ann Arbor.
"This is important information for pediatricians who are monitoring children for growth and development because the findings are potentially the opposite of what you see in girls," Lee said by email. "Pediatricians should consider the possibility that delayed puberty in boys may be due to obesity."
Previous research in girls has linked obesity to overproduction of the hormone estrogen, which can hasten puberty. But earlier studies in boys have not yielded clear explanations for how weight might influence their development, Lee and colleagues note in the journal Pediatrics.
For the current study, researchers analyzed data on boys' weight, height and testicular volume, an indication of the onset of puberty.
Out of about 3,900 boys in the study, roughly half were white, one quarter were black and another quarter were Hispanic.
Overall, about 60 percent of the boys were normal weight, while 17 percent were overweight and 23 percent were obese.
Researchers analyzed data on testicular volume and genital development to assess the median age when boys went through several stages of puberty, meaning the point when half of the boys had reached each development stage.
White boys who were overweight but not obese entered an early stage of puberty around 9.3 years old versus 10 years old for their normal-weight peers, and they also transitioned into later stages sooner, at around 14.5 years compared with 15.2 years, differences that were statistically meaningful.
Obese white boys entered the more advanced stages of puberty later at around 15.4 years old, a significant delay.
For black boys, obesity was linked to statistically meaningful delays at intermediate stages of puberty but not at the start or the end of the process.
There weren't any significant differences in the timing of puberty based on weight for Hispanic boys.
The study, based on a review of records from routine physicals done by pediatricians, wasn't designed to prove that excess pounds can change timing of puberty or explore why this might occur, the authors note. And the assessment of testicular volume and genital development in the study may not be as accurate as evaluations done by endocrinologists with expertise in sexual health.
Still, the findings offer yet another reason for parents and pediatricians to help children maintain a healthy weight through a balanced diet and regular exercise, the authors conclude.
"We want kids to maintain a healthy weight, and the effects on advancing or delaying puberty are relatively modest if anything," said Dr. Paul Kaplowitz, an endocrinologist at Children's National Health System in Washington, D.C. who wasn't involved in the study.
Bigger problems with obesity include insulin resistance, diabetes, heart disease and stress on muscles and bones, Kaplowitz added.
Boys who haven't gone through puberty by age 14 can take testosterone for several months to address the problem, Kaplowitz noted.
"We can't say obesity does or does not result in changes in the timing of puberty," Kaplowitz added. "We can say with obesity that prevention is key, and in many cases when we are too late for prevention, dietary changes and more exercise are very important."