For instance, studies have linked an early start to menstruation with an elevated risk of breast cancer. And other research has shown that girls who go through puberty early tend to have lower self-esteem and a poor body image. They are also more likely to engage in risky behaviors which can result in unplanned pregnancies, experts say.
It is currently unclear why younger girls are going into puberty. It is suggested that there are several factors involved. One is the rise in childhood obesity. Others propose environmental factors at play. Hormones in the milk, estrogens in plastic that sort of thing. Will switching to a greener and healthier lifestyle reverse the trend? They just don't know.
Linda Carroll has more: Link