The timing of puberty in boys may be influenced by how much they weigh, according to a new study. The research, published online Jan. 27 in the journal Pediatrics, found that overweight boys enter puberty earlier than normal weight boys, but in obese boys onset occurs later.
“We found something we didn’t expect, which is obese boys go later, but overweight boys seem to go earlier,” study author Joyce Lee, MD, MPH, an associate professor of pediatrics and public health at the University of Michigan in Ann Arbor, told HealthDay. “You would expect a linear relationship between weight and the timing of puberty, but we found that isn’t the case.”
Previous research has shown that overweight and obese girls tend to go through puberty earlier than girls of normal weight. This happens because the excess pounds stimulate increased estrogen, which can speed up puberty.
“When you have excess fat in the body, you have excess estrogen production in the body,” Lee explained. With this in mind, Lee and her colleagues sought to determine how excessive weight affected the pubertal process in boys.
For the study, the researchers followed 3,872 black, white and Hispanic boys ages 6-16. Each boy was measured for height and weight. Based on their body mass index (BMI), they were then classified as obese, overweight or normal.
Obese boys had a BMI that put them among the heaviest 5 percent of boys their age. Overweight boys had a BMI that placed them in the 85th to 95th percentile of their peers. Overall, 60 percent of the boys were of normal weight, 17 percent were overweight and 23 percent were obese.
The boys’ pubertal development was determined by testicular volume and genital development. White boys who were overweight saw the onset of puberty at around 9.3 years of age, compared to 10 years for their normal-weight peers. They also transitioned to completion of puberty sooner, at around 14.5 years versus 15.2 years for normal weight males.
Obese white boys completed puberty later, at 15.4 years. For black boys, obesity was linked statistically to meaningful delays at intermediate stages of puberty, but not at the start or completion of the process. There were no significant differences in the timing of puberty based on weight in Hispanic boys.
“…We speculate that it is possible that greater estrogen production in the obese boys could be suppressing the pubertal process for obese, but not overweight boys,” wrote the authors in the study’s conclusion.
The authors noted that the study was not designed to establish cause-and-effect between excessive weight and puberty timing. They also said that because their findings show the relationship between pubertal timing and body fat in boys is not clear cut there is a need for additional studies.
Still, Lee told MedPage Today in an email, that “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. Pediatricians should consider the possibility that delayed puberty in boys may be due to obesity.”
But Lee also urged parents of overweight and obese boys not to be worried about the study findings because all of the boys’ sexual development eventually happened within normal ranges. Of greater concern is the health consequences of carrying excess weight, cautioned Lee.
Obesity researcher Steven Heymsfield agreed. “Parents should be more worried about the lifelong bad influence that childhood obesity can have on their children’s health,” Heymsfield, a professor at Louisiana State University’ Pennington Biomedical Research Center, told HealthDay.
Autopsies of obese children have revealed hardening of the arteries in kids as young as 12, said Heymsfield, who was not involved in the study. “We know that adult chronic diseases begin in childhood. You definitely are pushing the envelope when you are obese as a child.”