NEW YORK (Reuters Life!) – Girls in the United States are hitting puberty at an earlier age with overweight youngsters tending to develop earlier, according to a US study. Cincinnati Children's Hospital Medical Center researchers compared 1,200 girls aged seven and eight in Cincinnati, New York and San Francisco with a similar 1997 study using a standard measure of breast development to determine which girls had started puberty. They found at age seven, about ten percent of white girls and 23 percent of black girls had started developing breasts which compared to five percent of white girls and 15 percent of black girls in 1997. This was consistent with earlier studies that found large differences in development based on race.

Among eight-year-olds in the study, 18 percent of white girls and 43 percent of black girls had entered puberty – an increase from around 11 percent of white girls from 1997 but the percentage of black girls was unchanged.

Researcher Frank Biro said rising rates of obesity could be a major reason why girls seem to be developing faster.

His team found that girls with a higher body mass index (BMI) – a ratio of weight and height – at age seven and eight were more likely to be developed than their thinner peers.

But he said doctors are worried about both the psychological and physical health of girls who hit puberty at a young age.

Studies have shown that girls who develop early are more at risk for depression and often start having sex earlier than girls who develop later.

In the second study, Dr. Mildred Maisonet from Emory University's Rollins School of Public Health and her colleagues found gaining weight quickly in infancy – a predictor of later obesity – was linked to early puberty in British girls.

Biro said another concern was that women who spend more of their lives menstruating are at a higher risk for breast cancer which, depending on when they hit menopause, and this could be a worry for girls who develop early.