Puberty is a natural part of growing up. But premature physical maturity (a.k.a. precocious puberty), currently on the rise among girls as young as age 7 or 8, could do more than trigger self-esteem issues—it may increased breast cancer risk later in life, according to a study published in Pediatrics and reported by msnbc.com.

For the study, researchers enrolled 1,239 girls ages 6 to 8 from three U.S. areas to determine the long-term effects of puberty and other factors on breast cancer. (Participants hailed from New York’s East Harlem, the Cincinnati metropolitan area and the San Francisco bay area.)

Scientists found 10 percent of 7-year-old white girls had some breast development compared with 5 percent in a similar study done in 1997. Meanwhile, 23 percent of the 7-year-old black girls started puberty compared with 15 percent in the 1997 study.

What’s causing this internal growth spurt? Medical professionals aren’t sure, but obesity could be the culprit, said Frank Biro, MD, lead study author and director of adolescent medicine at Cincinnati Children’s Hospital.

Other environmental factors may be at work too, explains Stanley Korenman, MD, an endocrinologist at the University of California in Los Angeles, who is not associated with the study. For example, girls’ bodies may be reacting to estrogen exposure from food, plastics and chemicals (estrogen stimulates breast development).

But until further research determines why precocious puberty has increased among girls, researchers recommend that families begin “living green” to help slow children’s premature physical maturity.

“It may help for families to eat together and to consume a well-balanced diet,” Biro said, adding that “regular physical activity may help, too.”

But the breast cancer connection isn’t the only concern. Other studies show that early puberty negatively affects self-esteem, emotional maturity, body image and even how tall children grow.

In addition, girls who undergo early puberty are more likely to engage in risky sexual behavior, and that can create other problems they are not emotionally mature enough to handle, researchers explained.

Learn which beauty product ingredients might affect girls’ puberty onset here.