Breast Density and Size
Does my weight affect my risk of breast cancer?
For postmenopausal women, weight is directly related to the risk of breast cancer. As a woman enters menopause, the ovaries stop producing estrogen, the key female sex hormone. However, the fat cells also produce estrogen, and they provide enzymes necessary to convert one of the key sex hormones, androstenedione, into estrone, a form of estrogen. High levels of estrone in the blood have their advantages: fewer hot flashes and other symptoms of menopause, fewer wrinkles, and denser and stronger bones. The downside is that some of the estrone is oxidized into hormones that send a strong signal to cells in the milk ducts, telling those cells to grow and divide.
Although the estrogens and their growth signals do not cause breast cancer itself, the acceleration of the cell growth and division process increases the chances that a cancer will develop as the result of an error in copying. That is, if any cell already contains cancer-causing mutations, those mutations will be passed on when the cell divides. As such, one mutated cell could grow into a mass of many mutated cells. This, in turn, could develop into a cancerous tumor. Women who have a greater percentage of body fat produce more estrone and, thus, are at greater risk for developing breast cancer.
When should I be concerned about weight gain?
A middle-aged woman who is slightly overweight -- that is, a woman who has a body mass index (BMI) of 25 to 27 -- has an average risk of getting breast cancer. If she lost 10–20 pounds and reduced her BMI to less than 25, her risk of breast cancer would decrease by six percent. Women with a BMI over 27 who reduce their weight can reduce their breast cancer risk by 15% or more. Weight loss also decreases the risk of other cancers, diabetes, and heart disease.
