Breast cancer survivors who gain weight may increase their risk of dying of the disease, reported scientists from the Kaiser Permanente Division of Research at the American Association for Cancer Research meeting on Tuesday.
Previous studies have tied excess weight to a heightened cancer risk; government researchers found recently that women who gain weight are more likely to develop breast cancer than those who maintain their weight throughout adulthood. Those findings included postmenopausal women who did not take hormone replacement therapy, which has been associated itself with increased risk.
While age may partly explain the trend — people tend to gain weight with age, and the risk of cancer increases with advancing years — the Kaiser group found that it was large amounts of weight gain that was linked to increased cancer risk. In the study of more than 18,000 breast cancer survivors, lean women who gained more than 10% of their pre-diagnosis body weight raised their risks of having a recurrence and of dying from breast cancer by 25%, compared with women whose weights fluctuated within 5% of their original measurement.
The reason for the connection isn’t clear, but it may have something to do with the hormone estrogen: excess fat cells may raise levels of estrogen, which is known to promote abnormal tissue growth in the breast. Overweight is also a marker for a number of other risk factors for cancer, including having a poor diet that is low in cancer-fighting antioxidants and a lack of physical exercise.
The findings don’t necessarily mean that everyone with middle-age creep is at higher risk of dying from cancer — the authors say that more work needs to be done to clarify whether there are thresholds of weight gain that trigger increases in risk, and more studies need to explain how weight and cancer are related.