More US girls are starting puberty younger, with large percentages developing breasts and pubic hair as early as seven, according to a study released on Monday in the American journal Pediatrics.
Nearly a quarter of black girls (23.4 per cent), 14.9 per cent of Hispanic girls and 10.4 per cent of white girls develop breasts by the age of seven, the study of 1239 girls in Harlem, Cincinnati and the San Francisco area found.
Twenty per cent of seven-year-old black girls had pubic hair, as did around 6.5 per cent of white and Hispanic girls, the study found.
The alarming figures are a big jump compared with a similar study published in 1997. Back then, only five per cent of seven-year-old white girls and around 15 per cent of black girls of the same age were developing breasts.
Negative impacts associated with early puberty in girls include increased risk of breast or endometrial cancer later in life, and psychological troubles ranging from low self-esteem and eating problems to depression and suicide.
Just what causes puberty to start is not fully understood, and the researchers plan to pool data collected for the study to try to determine if there are associations between puberty onset and factors such as diet or exposure to endocrine-disrupting chemicals.
The study, led by Frank Biro of the Cincinnati Children's Hospital's adolescent medicine division, also said girls who hit puberty young are "more likely to be influenced by deviant peers" and become sexually active earlier.
The study found that at age eight, more than four in 10 black girls (42.9 per cent) were developing breasts and nearly a third had pubic hair.
Nearly 31 per cent of Hispanic girls and 18 per cent of white girls were developing breasts at the age of eight, and 19 and 10 per cent respectively had pubic hair.
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