Earlier puberty for overweight girls?

[illusionofjoy]

According to an Associated Press article, girls who are overweight tend to start puberty sooner and become women who are overweight. Okay, that second point is pretty much a no-brainer, but I'm wondering what exactly the trigger is between fat and menstruation, should one actually exist.

Overall, I've noticed a frightening rise in the level of physical maturation in young girls over the years. I think something is wrong when a ten year old has breasts that are nearly fully developed. I don't remember seeing any breasts until 7^th or 8^th grade...but then again, I wasn't in much of a position or inclination to go "boobie-spotting" until my waning years of middle school anyhow.

In any case, given that a lot of these girls aren't fat, I'm more inclined to blame chemicals in the groundwater or something similar than just fat.