New research from Denmark shows that girls are reaching puberty earlier than ever before, at age 9. While some fear this will lead to increased sexual activity at a younger age, others are more concerned about what’s causing girls to develop breasts and have their periods so soon. Scientists point to chemicals in the food chain along with obesity and a high meat diet for the change.

The study of 1,000 girls found that on average breast development started at 9 years and 10 months, while a similar look at puberty in 1991 showed it occurred a year later.

The onset of puberty has been lowering at a steady rate for decades. It occurred around age 15 in girls during the 19th century and at age 12 1/2 in the 1960s.

“We were very surprised that there had been such a change in a period of just 15 years,” Anders Juul, head of the Department of Growth and Reproduction at the University hospital in Copenhagen told The Sunday Times. “It’s a clear sign that something is affecting our children, whether it’s junk food, environmental chemicals or lack of physical activity.”

Bisphenol A (BPA) is one of the chemicals most often blamed for interferring with hormones and sexual development. BPA can start building up in girls when they’re merely a fetus, and the chemical is found in common places such as canned foods and plastic baby bottles. The Danish scientists are continuing their research to look for a direct link between puberty and BPA.

Diet is likely also to blame. Brighton University researchers found a link between high meat consumption and early puberty in girls. The study of 3,000 12-year-old girls, which was published in the journal Public Health Nutrition earlier this month, found that 49% of girls who ate meat 12 times a week at age 7 started their periods by age 12 1/2, while only 35% of girls who ate meat 4 times a week or less reached puberty by age 12 1/2.

Research has shown that those who reach puberty earlier are at greater risk for breast cancer and heart disease. Further studies are needed to nail down the cause of the early puberty phenomenon, but at this point, sticking to a healthy diet and avoiding BPA couldn’t hurt.

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