Breast cancer is one of the important cancers for which obesity is a risk factor. Little is known about what causes these cancers, and what is known often isn't modifiable, such as inherited risk, or age when a woman's periods start. Edward Giovannucci, an associate professor and epidemiologist at Harvard University Medical School, agreed. But for specific cancers, it's a significant factor. Obesity also is clearly a risk factor for breast cancer in women after menopause, he said.
Obesity usually is defined by body mass index, a formula based on height and weight.
A BMI of 25 and above is considered overweight, and 30 and above is obese, according to standards set by the National Institutes of Health. Obesity's ability to raise the risk of a whole range of health factors is long established, and the cancer society report reviews those. There are theories but the bottom line is, it's unknown. And previous studies suggest that more than a third of cancer deaths are related to dietary factors, such as eating enough fruits and vegetables and minimizing fat intake - factors that have much to do with obesity. There's also evidence that obesity is more of a cancer risk factor for women than men.