Childhood Obesity Tied to Earlier Puberty in Girls
Study compared onset age of breast development in 1997 and now
But it is clear that childhood obesity has consequences, said Vuguin, who was not involved in the study. "For parents, the message is to pay more attention to a healthy diet and exercise even in a child's early years," she said.
The findings are based on 1,200 girls from three U.S. cities who were followed between 2004 and 2011. Black girls started developing breasts around age 8, while Hispanic, white and Asian girls typically started at age 9.
When Biro's team compared their findings with the 1997 study, they found that white girls were clearly maturing faster in recent years. Twenty-one percent had started developing breasts before age 9, versus 11 percent in the earlier study, for example.
Black girls seemed to be developing earlier too: 22 percent started before age 8, versus 15 percent in 1997. But that difference was not significant in statistical terms, Biro said.
"What seems to be happening is that white girls are 'catching up' with black girls," he said.
From the data, it appeared that increasing body weight accounted for much of the difference between the two studies, Biro said. But excess pounds did not tell the whole story, he said.
It's possible that other factors are at work, Biro said, including various environmental chemicals that can disrupt hormone activity, such as certain pesticides and plasticizers. Lack of exercise and childhood diets that are low in fiber and high in meat and dairy also have been suspected of contributing to earlier puberty. But none of those suspicions has yet been proven.
Vuguin said research like this is important for doctors because they need to keep evaluating what "normal" development is. There is a difference between relatively earlier puberty and what doctors call "precocious puberty" -- which can have consequences such as stunted growth because the bones stop maturing earlier than normal.
Traditionally, Vuguin said, precocious puberty has been defined as signs of puberty -- including breast development -- before the age of 8 in girls. Doctors may use hormonal medications to treat it.
"But if you have, for example, an obese African-American girl who is developing breasts at the age of 7, that might be 'normal' now," Vuguin said. "I think there is starting to be a shift in how we're looking at this: Should we treat it, or let it be? It's complicated."