Obesity and Breast Cancer: The Estrogen Connection

The data on breast cancer incidence and its relationship to obesity is complex and often surprising. Prior to menopause, the fact is that obese women have lower odds of developing the disease than women whose weight is in the acceptable range (with a BMI of 25 or less).

After menopause, though, the situation is reversed, and the incidence among obese women jumps to 150 percent that of women of healthy weight. This increase is blamed largely on the increase in estrogen levels. Research has shown that obese women produce abnormally high levels of estrogen. While the ovaries are the main source of estrogen prior to menopause, fat tissue becomes the source of estrogen after menopause. This is why the odds appear to increase. The likelihood of developing breast cancer is about equal among women taking hormone replacement therapy (HRT), whether they are obese or of normal weight.

Hormone Replacement Therapy: Is It For You? Until the summer of 2002, doctors regularly recommended hormone replacement therapy (HRT) for women approaching menopause. Millions of women and their physicians assumed that the slightly increased risk of breast cancer was largely offset by the decreased risk of heart disease that was thought to be the effect of maintaining estrogen levels at pre-menopausal levels. Heart disease has become the number one killer of women. New research showed, though, that the decreased incidence of heart disease was not significant enough to warrant HRT for periods of a decade or more. In fact, HRT appeared to increase rather than decrease the risk of a number of diseases. For some women, the extra estrogen appears to play a role in the development of breast cancer. If you're taking HRT or birth control pills, talk to your physician about your risks. For more information, read about the HRT Debate.

 

While obese women appear to have increased odds of developing the disease, research data show that body mass index (BMI) is a less important factor in assessing risk than weight gained during adulthood.

The distribution of body fat is another measure used to predict a woman's chance of getting breast cancer. Women with abdominal fat appear to be at higher risk than women whose fat is distributed over the hips, legs and buttocks.

While specific studies of minority women's risks of breast cancer are not numerous, some research results suggest that African American women who are obese are no more likely to get it than women of healthy weight.

In addition to the hormonal effects of being overweight, excess fat deposits in the breasts also make it more difficult to detect small lumps during examination which can delay early detection of the disease. Visit Breast Cancer for information on the disease, its detection and treatment.