Gaining weight may be a serious risk factor for breast cancer. The findings of a recent study illustrate the importance of maintaining a healthy body weight throughout life. Researchers from the American Cancer Society based their study on a survey that begun in 1992, when women aged 50 to 74 were asked their current weight, as well as their weight at the age of 18. They were followed for several years. It was found that women who gained 21 to 30 pounds after the age of 18 were forty percent more likely to get breast cancer than women who gained 5 pounds or less. Women who gained more than 70 pounds had twice the risk of cancer of women who stayed within 5 pounds of what they weighed at 18. Even modest weight gain since age 18 was found to be associated with an increased risk of postmenopausal breast cancer. The findings support the idea that body fat increases the risk of breast cancer by increasing the levels of the hormone oestrogen. Lean women not using HRT have the lowest levels of circulating oestrogen, and the lowest risk of breast cancer. Women who used hormone replacement therapy did not show the same effects, the researchers found. HRT users, both lean and fat, have high levels of circulating hormones, masking any additional oestrogenic effect from fat cells. Being overweight has been known to put women at higher risk of breast cancer, but the current study offers additional details of how and why.

Cancer Epidemiology, Biomarkers and Prevention,
February 2004