Lifestyle-related Factors and Breast Cancer Risk
Not having children: Women who have had no children or who had their first child after age 30 have a slightly higher breast cancer risk.
Oral contraceptive use: It is still not clear what part oral contraceptives (birth control pills) might play in breast cancer risk. Studies have found that women now using oral contraceptives have a slightly greater risk of breast cancer than women not using them. Women who stopped using oral contraceptives more than 10 years ago do not appear to have any increased breast cancer risk. When considering using oral contraceptives, women should discuss their other risk factors for breast cancer with their health care team.
Hormone replacement therapy: Most studies suggest that long-term use (5 years or more) of hormone replacement therapy (HRT) after menopause will increase your risk of breast cancer. If you still have your uterus (womb), doctors generally prescribe estrogen and progesterone. Estrogen is prescribed to prevent menopausal symptoms and osteoporosis. It, however, can increase the risk of developing cancer of the uterus. Progesterone helps prevent cancer of the uterus.
If you no longer have your uterus, then only estrogen is prescribed. Several studies have found that the increased risk of breast cancer related to combined HRT is mostly due to the progesterone. Estrogen alone does not appear to increase the risk as much.
The risk of HRT applies only to current and recent users, and a woman's breast cancer risk appears to return to that of the general population within 5 years of stopping HRT.
The decision to use hormone replacement therapy after menopause should be made by the woman and her doctor after weighing the possible risks and benefits. Factors to consider include your other risk factors for breast cancer, osteoporosis (thinning and weakening of bones), and the severity of menopausal symptoms. HRT increases the risk of blood clots and strokes. It reduces the risk of bone fractures and colon cancer.
Breast feeding: Many studies have shown that breast feeding lowers breast cancer risk. A recent study of over 100,000 women concluded that for every 12 months of breast feeding a woman lowers her risk of breast cancer by 4.3%. The study also found that every birth reduced a womans breast cancer risk by 7%.
The explanation of this may be that both pregnancy and active breast feeding reduce a womans total number of lifetime menstrual cycles. This may be similar to the reduction of risk due to late menarche (start of menstrual periods) or early menopause, which also decrease the total number of menstrual cycles. The study concluded that having more children and breast feeding longer could reduce the risk of breast cancer by half.
Alcohol: Drinking alcoholic beverages clearly increases the risk of developing breast cancer. Compared with nondrinkers, women who consume 1 alcoholic drink a day have a very small increase in risk, and those who have 2 to 5 drinks daily have about 1 times the risk of women who drink no alcohol. Alcohol is also known to increase the risk of developing cancers of the mouth, throat, and esophagus. We recommend limiting your consumption of alcohol, if you drink at all.
Obesity and high-fat diets: Obesity (being overweight) is associated with an increased risk of developing breast cancer, especially for women after menopause (which usually occurs at age 50). Although your ovaries produce most of your estrogen, fat tissue can change some other hormones into estrogen. Having more fat tissue can increase your estrogen levels and increase your likelihood of developing breast cancer.
The connection between weight and breast cancer risk is complex, however. For example, risk appears to be increased for women who gained weight as an adult but is not increased among those who have been overweight since childhood. Also, excess fat in the waist area affects risk more than the same amount of fat in the hips and thighs. Researchers believe that fat cells in various parts of the body have subtle differences in their metabolism that may explain this observation.
Studies of fat in the diet and breast cancer risk have often given conflicting results. Most studies found that breast cancer is less common in countries where the typical diet is low in total fat, low in polyunsaturated fat, and low in saturated fat.
On the other hand, many studies of women in the United States have not found breast cancer risk to be related to dietary fat intake. Researchers are still not sure how to explain this apparent disagreement. Many scientists note that studies comparing diet and breast cancer risk in different countries are complicated by other differences (such as activity level, intake of other nutrients, genetic factors) that might also alter breast cancer risk.
More research is needed to better understand the effect of the types of fat eaten and body weight on breast cancer risk. But, these factors have been shown to influence the risk of developing several other types of cancer, and intake of certain types of fat is clearly related to heart disease risk. We recommend you maintain a healthy weight and limit your intake of red meats, especially those high in fat or processed.
Physical inactivity: Exercise and cancer is a relatively new area of research. Recent studies show that strenuous exercise in your youth might provide life-long protection against breast cancer and that even moderate to strenuous physical activity as an adult can lower breast cancer risk. More research is being done to confirm these findings.
Environmental pollution: A great deal of research has been reported and more is being done to understand environmental influences on breast cancer risk. The goal is to determine their possible relationships to breast cancer.
Currently, research does not show a clear link between breast cancer risk and exposure to environmental pollutants, such as the pesticide DDE (chemically related to DDT), and PCBs (polychlorinated biphenyls). Although a few studies have suggested certain pollutants increase breast cancer risk, most experts believe that if such a connection exists, it accounts for a very small portion of breast cancer cases.