Obesity and Early Puberty: What's the Risk?

About 1 in 5,000 children experience early puberty. Studies suggest that, on average, kids are starting puberty earlier than they once did. Could the rise in obesity be playing a role? Many experts think so, at least when it comes to girls.

"I think it's quite clear that some of the early puberty we're seeing is related to obesity," says Paul Kaplowitz, MD, PhD, chief of the division of endocrinology at Children's National Medical Center in Washington, D.C. "It's not the whole story, but it's a factor."

What's the association between obesity and precocious puberty? How might it affect your child? Here's what you need to know.

Obesity and Early Puberty: What's the Evidence?

When puberty starts in girls younger than 8 or boys younger than 9, it's considered early, or precocious puberty. In girls at least, research suggests a possible link between early puberty and obesity.

"A number of studies have shown that girls who are overweight are more likely to have puberty early, and that girls who are underweight -- and especially anorexic -- undergo puberty later," says Kaplowitz.

What about boys? So far, there's no evidence that obesity raises the odds of early puberty for them. "Boys who are obese actually tend to hit puberty later than average," says Jami Josefson, MD, a pediatric endocrinologist at Children's Memorial Hospital in Chicago.

Average Age of Puberty Is Dropping

Studies show that the average age of puberty may be dropping over the years. The age at which a girl first gets her period seems to have stayed roughly the same for decades. But breast development -- usually the first sign of puberty in girls -- might be starting a year or so earlier than it once did.

 

How Might Obesity Affect Early Puberty?

One possible explanation for the association between obesity and early puberty has to do with the hormone leptin, says Kaplowitz.

Our fat cells make leptin. The more fat we have, the more leptin in our systems. Leptin seems to play a key role in regulating appetite, body type, and reproduction.

Leptin doesn't trigger puberty on its own. But there's evidence that for puberty to start, a child has to have enough leptin in her system, Kaplowitz says. Girls who have high leptin levels -- because they are overweight -- could be more prone to early puberty.

Biological changes in young babies could have a lasting effect, too. Studies have indicated that rapid weight gain during infancy might be related to later obesity and a higher risk of early puberty.

There's another very different link. Obesity can cause some kids who don't actually have early puberty to get diagnosed with it anyway. Why? Sometimes, pediatricians mistake fat for breast development in girls.

Researchers note that the earlier age of puberty seems to go along with the rise of obesity in the U.S. In 1965, about 5% of kids ages 6-11 were obese. In 2008, it was almost 20%.

However, while they might be linked, we can't say that obesity is necessary causing early puberty. Obesity is not the only factor. Kaplowitz points out that even in countries where childhood obesity is less common, puberty seems to be starting earlier.

A 2009 Danish study found that over the course of 15 years, the average age at which girls showed breast development dropped a whole year -- from nearly 11 years old to just under 10 years old. Rates of obesity are much lower in Denmark than in the U.S.

So if obesity isn't the sole cause, what else might be making puberty start earlier? Experts just don't know.