Breast cancer & weight.

The weight you lose or gain may alter your risk of breast cancer if you don't take estrogen pills, says a study that tracked more than 87,000 women for up to 24 years.

Weight gain or loss had little impact on women who had taken postmenopausal hormones. But among women who had never taken hormones, the risk of breast cancer was:

* 57 percent lower in those who had lost at least 22 pounds since menopause than in similar women with steady weights.

* 50 percent higher in those who had gained at least 44 pounds since age 18 than in similar women who had gained little or no weight since their late teens. (Weight gain after menopause didn't alter breast cancer risk significantly.)

The researchers estimate that, among women who never took hormones, 24 percent of breast cancer cases are due to gaining more than four pounds after age 18, and 8 percent are due to gaining more than four pounds after menopause.

What to do: Lose excess weight. It's never too late. Excess weight may increase the risk of breast cancer by boosting estrogen levels. In postmenopausal women who don't take hormones, fat cells are the biggest source of estrogen. And more fat means more estrogen.

Women who take hormones also have higher levels of estrogen, which increases their breast cancer risk. But the estrogen produced by their fat cells doesn't seem to raise the risk further.

J. Am. Med. Assoc. 296: 193, 2006.