Updated on 7/29/2005
Yes, the connection between being overweight and the risk of certain types of cancers has been known for some time, but the results you refer to tell us much more than we had known before. This was a huge study in which researchers from the American Cancer Society tracked 900,000 people for 16 years to determine the role of weight in cancer deaths. They found that being overweight or obese may account for 20 percent of all cancer deaths among women in the United States and 14 percent of all cancer deaths among men in this country. If we didn't have the current obesity epidemic, a great many cancer deaths might be prevented.
This study also identified certain types of cancer that we previously only suspected were associated with excess body weight: cancers of the liver, pancreas, prostate, cervix, ovary and stomach (in men) as well as non-Hodgkin's lymphoma and multiple myeloma. We have known for some time that breast cancer among postmenopausal women as well as cancer of the uterus, kidney, esophagus, gallbladder, colon and rectum and are more common in overweight individuals.
No one knows exactly why obesity affects cancer risks. Excess body fat may raise certain hormone levels in the body. These may include sex hormones such as estrogen associated with breast and uterine cancer, or hormones that regulate metabolism, such as insulin. For example, too much body fat around the waist is associated with insulin resistance, which has been linked to an increased risk of colon cancer.
This study actually gives us some good news because it points to a way to lower cancer deaths. Some cancer risks are beyond our control. For example, for women the biggest risks of breast cancer are being female and getting older. Controlling weight is not always easy, but reducing cancer risk may increase motivation to do so.
Andrew Weil, M.D.