Childhood obesity linked to later onset of puberty in boys

A new study led by researchers at the University of Michigan Health System suggests that excess body weight may lead to a later onset of puberty in boys.

The study in the February 2010 issue of the Archives of Pediatrics and Adolescent Medicine found boys who were obese or overweight were twice as likely to have delayed puberty as those who had a normal body mass index.

For the study, U-M pediatric endocrinologist Joyce M. Lee, M.D., M.P.H., and colleagues looked at 401 boys who were born in 1991 and came from diverse socioeconomic backgrounds in 10 regions of the U.S.  The researchers measured their height and weight from ages 2 to 12 years.

Puberty was measured by Tanner genitalia staging.  On the scale, boys in stage 1, defined as lack of genital development by 11.5 years of age, are considered having later onset of puberty.

The results of the study showed that of the obese boys, 14 percent had later onset of puberty compared to 13.3 percent for those who were overweight and 7 percent for those who had a normal body mass index.

Early studies have associated childhood obesity with early onset of puberty in girls. In the U.S., some doctors consider it normal for girls to enter puberty at the age of as early as 8 years.

"Our findings have important implications for understanding sex differences in physiological mechanisms of puberty,” said Lee.

A health observer suggested that obesity is a symptom, but not a cause for later puberty in boys and early puberty in girls.  He said that delayed puberty in boys suggests an inadequate ratio of the male hormones to female hormones.  Boys are supposed to develop into a stage in which they have more male hormones than female hormones. For girls, the opposite is true.

He blamed the widespread use of dairy products and meats for the unconventional reproductive development.

A Mongolian scientist working at Harvard told colleagues in an earlier presentation that U.S. milk may have higher estrogen levels than Mongolian milk as US farmers collect milk even during a period in which dairy cows produce high levels of estrogen in their milk.   She suggested that these natural hormones can be up to 10,000 times more effective than those hormone analogs found as environmental pollutants.

By David Liu and editing by Denise Reynolds