Obesity protects against breast cancer

Being overweight or obese from adolescence to menopause reduces a woman’s chances of getting breast cancer, researchers at Harvard Medical School have found. The earlier in life that the researchers looked, the stronger the association, leading to the conclusion that a woman’s weight at age 18 is a strong predictor of breast cancer.

In this body size-breast cancer connection, risks are calculated by a height-to-weight comparison known as body mass index, or BMI. Men and women with a BMI lower than 25 are considered normal, as far as their weight is concerned. A BMI between 25 and 30 raises someone to overweight status. Higher than 30 earns an obese rating. Women with a BMI of 27.5 or higher have 43 percent less chance of getting breast cancer than those who fall between 20 and 22, according to the new study.

To compute your BMI, convert your weight to kilograms (1 pound equals 0.45 kilogram) and your height into meters (1 meter equals 3.3 feet), and then divide your weight by the square of your height (your height multiplied by itself). To give some idea of the actual sizes involved, a 5-foot, 7-inch woman with a BMI of 20 weighs 127 pounds. BMIs of 25, 27.5, and 30 or more raise weights to 159, 175, and 191-plus pounds.

This finding doesn’t mean that it’s OK for younger women to binge on french fries and chocolate. Other studies suggest that, for women, the risk of death from all causes increases for every pound of weight above the normal range. Obesity doubles to triples that risk.

Also, protection from breast cancer reverses after menopause. Then, overweight women have a much higher risk for breast cancer than thin women. ‘Although a high birth weight is fairly consistently linked to an increase in premenopausal breast cancer, things seem to reverse around puberty,’ notes Karin B. Michels, an associate professor of obstetrics, gynecology, and reproductive biology who led the study. ‘We don’t know exactly when the reverse occurs, but then it reverses again after menopause.’