"A new study finds that girls are more likely today than in the past to start developing breasts by age 7 or 8.
The research is just the latest in a flood of reports over the last decade that have led to concern and heated debate about whether girls are reaching puberty earlier, and why it might be happening.
Increased rates of obesity are thought to play a major role, because body fat can produce sex hormones. Some researchers also suspect that environmental chemicals that mimic the effects of estrogen may be speeding up the clock on puberty, but that idea is unproved.
The issue is of concern for both medical and psychosocial reasons. Studies suggest that earlier puberty, as measured by the age at first menstruation, can slightly increase the risk of breast cancer, probably because it results in longer lifetime exposure to the hormones estrogen and progesterone, which can feed some tumors.
Although the new study did not look at menstrual age, breast growth is also a sign of hormone exposure, and some researchers fear that early development might also mean an increased cancer risk. "
Denise Grady reports for the New York Times August 9, 2010.