CHICAGO — When it comes to the birds and the bees, some parents may want to have that talk with their boys a little sooner than they had expected.
Researchers have found signs of puberty in American boys up to two years earlier than previously reported — age 9 on average for blacks and age 10 for whites and Hispanics. Other studies have suggested that girls, too, are entering puberty earlier.
Why is this happening? Theories range from higher levels of obesity and inactivity to chemicals in food and water, all of which might interfere with normal hormone production. But those are just theories.
Doctors say earlier puberty is not necessarily a cause for concern. And some experts question whether the data are reliable.
Dr. William Adelman, an adolescent medicine specialist in the Baltimore area, says the research is the first to find strong physical evidence that boys are maturing earlier. But he added that the study still isn't proof.
Earlier research based on 20-year-old data also suggested a trend toward early puberty in boys, but it was based on less rigorous information. The new study involved testes measurements in 4,000 boys. Enlargement of testes is generally the earliest sign of puberty in boys.
The study was published online today in Pediatrics to coincide with the American Academy of Pediatrics' national conference in New Orleans.
Dr. Neerav Desai, an adolescent medicine specialist at Vanderbilt University in Nashville, said it's important for parents and doctors to be aware of earlier puberty in boys so that they can help children prepare emotionally for the changes. Doctors generally consider puberty to be early if it begins before age 8 in girls and before age 9 in boys.
Boys are more likely than girls to have an underlying physical cause for early puberty. But it's likely that most, if not all, of the boys in the study were free of any conditions that might explain the results because the boys were screened for physical ailments, said lead author Marcia Herman-Giddens, a researcher at the University of North Carolina in Chapel Hill.
For the study, researchers recruited pediatricians in 41 states. Doctors asked parents and boys ages 6 to 16 to take part during checkups. The visits took place between 2005 and 2010.
Half of the boys were white. The rest were almost evenly divided among blacks and Hispanics.
On average, the white boys started puberty at age 10, a year and a half earlier than what has long been considered the normal average. For black boys, the average age of 9 was about two years earlier than in previous research. Among Hispanics, the average age of 10 was similar to findings in previous research.
Testes enlargement was seen at age 6 in 9 percent of white boys, almost 20 percent of blacks and 7 percent of Hispanics.
Pubic hair growth, another early sign of puberty, started about a year after testes enlargement in all groups but still earlier than previously thought.