The Big Issue with Breast Cancer: How Your Weight Affects Your Risk

The Link Between Fat and Cancer

Our complicated emotions about weight can have dangerous consequences. Fat isn't just a lump of pounds -- it's a biologically active substance that produces hormones like estrogen, which promotes tumor growth. "The more fat you have, especially around the abdomen, the more estrogen you'll produce," says Sharon Rosenbaum Smith, MD, medical director of the Comprehensive Breast Center at St. Luke's-Roosevelt Hospital Center in New York City. Exposure to high levels of the hormone may increase a woman's chances of getting breast cancer over time. In a recent Harvard study, women who gained 55 pounds or more after age 18 had about a one and a half times greater likelihood of developing the disease postmenopause than those who stayed at a healthy weight.

Fat may also play a role in producing chronic inflammation, which can lead to a number of diseases, including breast cancer. "Fat tissue has a direct connection to the immune system," explains Kristin Campbell, PhD, assistant professor of physical therapy at the University of British Columbia in Vancouver. "It appears to send out signals that trigger inflammation," which may cause tumors to form.

In addition, overweight women are more likely to suffer from metabolic syndrome, a combination of conditions -- including high blood pressure and high cholesterol -- that can raise a woman's risk for heart disease, stroke, diabetes and, according to a brand-new study, breast cancer. Researchers suspect that one of the culprits in this case is insulin. "When people are inactive or overweight, they store the glucose they get from food in fat rather than in muscle," Irwin notes. Higher amounts of body fat amp up the body's production of estrogen as well as a chemical called insulin-like growth factor, both of which cause breast cells to grow rapidly, increasing the odds that cancer will develop. "Even being thin may not help if you're a couch potato," Irwin says.