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CANCER
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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. Having multiple pregnancies and becoming pregnant at an early age reduces breast cancer risk.
Oral contraceptive use: It is still not certain what part oral contraceptives (birth control pills) might play in breast cancer risk. Studies have suggested that women now using oral contraceptives have a slightly greater risk of breast cancer than women who have never used 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: It has become clear that long-term use (several years or more) of hormone replacement therapy (HRT) after menopause, particularly estrogens and progesterone combined increase your risk of breast cancer. They may also increase your chances of dying of breast cancer.
If you still have your uterus (womb), doctors generally prescribe estrogen and progesterone (known as combined HRT). Estrogen relieves menopausal symptoms and delays osteoporosis (thinning of the bones that can lead to fractures). But estrogen can increase the risk of developing cancer of the uterus. Progesterone is added to help prevent this.
If you no longer have your uterus, estrogen alone can be prescribed. This is commonly known as estrogen replacement therapy (ERT). This probably does not increase the risk of breast cancer very much, if at all.
Several large studies, including the Women's Health Initiative (WHI), have found that there is an increased risk of breast cancer related to the use of combined HRT. The most recent results from the WHI found that not only did combined HRT increase breast cancer risk, but it also increased the likelihood that the cancer would be found at a more advanced stage. This is because it appeared to reduce the effectiveness of mammography, as more abnormal findings on mammograms were noted. A large study from the United Kingdom has now found that women who took the combined therapy were also more likely to die of breast cancer than women who didn't.
The risk of HRT appears to apply only to current and recent users, and a woman's breast cancer risk seems to return to that of the general population within 5 years of stopping HRT.
Estrogen alone (ERT) does not appear to increase the risk of developing breast cancer. In fact, a separate part of the large WHI study found that it may slightly decrease the risk (although it was linked to an increased risk of stroke).
At this time there appear to be few strong reasons to use hormone replacement therapy (combined HRT or ERT), other than possibly for the temporary relief of menopausal symptoms. In addition to the increased risk of breast cancer, the WHI found that combined HRT also increased the risk of heart disease, blood clots, and strokes, and did not have a beneficial effect on mental function or preventing Alzheimer's disease. It did lower the risk of colorectal cancer and osteoporosis, but this must be weighed against the possible harms, and with the understanding that there are other effective ways to prevent osteoporosis. And, as noted above, while ERT did not seem to have much effect on the risk of breast cancer, it did increase the risk of stroke.
The decision to use hormone replacement therapy after menopause should be made by the woman and her doctor after weighing the possible risks (including increased risk of heart disease, breast cancer, strokes, and blood clots) and benefits (relief of menopausal symptoms, reduced risk of osteoporosis), and considering each womanÂ's other risk factors for heart disease, breast cancer, osteoporosis, and the severity of her menopausal symptoms.
Breast-feeding and pregnancy: Some studies suggest that breast-feeding may slightly lower breast cancer risk, especially if breast-feeding is continued for 1.5 to 2 years. Other studies found no impact on breast cancer risk.
The explanation of this may be that both pregnancy and breast-feeding reduce a woman's 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. One study concluded that having more children and breast-feeding longer could reduce the risk of breast cancer by half.
Alcohol: Use of alcohol is clearly linked to an increased risk of developing breast cancer. The risk increases with the amount of alcohol consumed. 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 1½ 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. The American Cancer Society recommends limiting your consumption of alcohol.
Obesity and high-fat diets: Obesity (being overweight) has been found to be a breast cancer risk in all studies, especially for women after menopause. Although your ovaries produce most of your estrogen, fat tissue produces a small amount of 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 may affect 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 have not clearly shown that this is a breast cancer risk factor. 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 it is clear that calories do count and fat is a major source of these. A diet high in fat has also 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 activity: Evidence is growing that physical activity in the form of exercise reduces breast cancer risk. The only question is how much exercise is needed. In one study from the WomenÂ's Health Initiative as little as 1.25 to 2.5 hours per week of brisk walking reduced a woman's risk by 18%. Walking 10 hours a week reduced the risk a little more.
