A study following over 400 boys shows that those who are obese are twice as likely as their normal-weight counterparts not to have started puberty by the age of 11 and a half. While previous studies in girls had shown the opposite phenomenon -- girls who are obese tend to hit puberty earlier than their normal-weight counterparts -- it seems obesity may cause a maturity delay in boys, a situation with unknown and possibly far-reaching effects.
"With the epidemic of childhood obesity, there's concern this is going to have a negative effect on growth and development," said Dr. Joyce Lee, a pediatric endocrinologist at the University of Michigan and the study's lead author.
Lee said that while girls have been well studied when it comes to the effects of early obesity, "there was a paucity of studies in boys."
In the new study, which was published in the Archives of Pediatric and Adolescent Medicine, it was found that 14 percent of obese boys had not started puberty by the end of the study, while only 7 percent of normal weight boys had not.
"This could add a further burden to obese, adolescent boys," said Dr. David Ludwig, director of the obesity program at Children's Hospital in Boston. "For [a boy] that may already be teased because of his appearance, delayed puberty could further increase the stigmatization."
He said that while the findings of this study are new, they confirm an observation some had made when working with obese boys.
"It may not be a well-recognized phenomenon but it is one that had been considered previously," Ludwig said.
"It's pretty well established in girls that puberty starts earlier [if they are obese]. The studies in boys really weren't as clear," said, Dr. Jennifer Helmcamp, a pediatrician specializing in obesity with Scott & White Healthcare. "This really helps say, delayed puberty may actually be caused by something that's going on because of this weight."
But while we may now know another potential consequence of obesity, Helmcamp notes that we still do not know what is causing it.
"There still needs to be more studies, we can't say for sure," she said.
One thing the results do is cast doubt on the hormone leptin, which is found in greater levels in people with more fat and was a suspect for the early puberty in girls who are obese. Because the hormone was found in high levels in both boys and girls, it appears less likely as an explanation for the changes in time of puberty because of obesity.
Ludwig said one possible reason obesity has an apparently opposite impact in boys and girls is that it appears that fat tissue converts male hormones into the female hormone estrogen, which could speed up puberty in girls but delay it in boys.
Because so little research has been done on the effects of obesity on boys when it comes to puberty, it is unclear what impact this new finding will have.
Lee said that while this study gives some indication that puberty works differently in boys and girls, it also means that we know less about what the possible impact might be on boys, or what the impact might be if obesity trends continue and girls, already ahead when it comes to puberty, move even further ahead of their males counterparts at the same ages.
All this study does, she said, is "It confirms that obesity has effects on children's growth and development for both genders."
Several researchers noted that early puberty has been shown to have an effect on fertility, and having more sex hormones may have an impact on future cancer risks.
Tom Baranowski, a professor of pediatrics specializing in behavioral nutrition at the Baylor College of Medicine, explained that the problem may come for boys who hit puberty earlier than their peers rather than those who see it delayed.
"The fear has been that the boys who experience puberty earlier would not have peers they could bounce their experience off of," he said. "They're forced into probably doing upwards comparisons. There's a risk that they run of running into children we might not prefer that they talk to."
Explaining exactly how obesity affects puberty may be far off, but one benefit of the study, Lee said, is it alerts parents to more immediate effects of obesity, rather than the further off risks like cardiovascular disease and diabetes, which may appear to be more abstract.
"I think the fact that obesity could affect how they currently grow and develop could be of greater concern to parents because that affects them in the short term," she said.