A study of 1,359 Japanese breast cancer patients and 24,000 healthy women found that excessive weight gain is strongly associated with increased breast cancer risk in post-menopausal women.
Researchers from the Aichi Cancer Center Research Institute in Nagoya found little or no connection between body mass index (ratio of weight to height) and risk for breast cancer among pre-menopausal women, but found that post-menopausal women’s risk of breast cancer is “markedly increased by obesity.” The heaviest 20% of the research subjects had more than double the risk for breast cancer than did the thinnest 20%.
Explanations for these findings are inexact. First, women who are chronically overweight may suffer greater risk due to “dietary and environmental factors.” Second, researchers suspect that post-menopausal weight gain may affect circulating estrogens, which have been linked with breast cancer.
The research report, published in January’s International Journal of Cancer, called for more research to confirm or disprove the current findings. “It is possible that the timing of weight gain may be critical in determining the association between weight change and breast cancer,” concluded the report.