Risk Factors That Are Lifestyle Related

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Not having children (parity) or late pregnancies
Women who have had no children (nulliparity) or who had their first child after age 35 have a higher breast cancer risk.

Breastfeeding
Having multiple pregnancies and becoming pregnant at an early age reduces breast cancer risk. This is because when women breast feed their babies their oestrogen level reduces, hence reducing the possibility of breast cancer risk.

Another theory is that pregnancy changes the lobules (the milk producing glands) inside the breast, and that the lobules of women who have carried a pregnancy to term differ from those of a woman who has not been pregnant. Thus, it may be that breast-feeding reduces breast cancer risk by changing the mammary gland in specific ways. And another theory is that breast-feeding reduces breast cancer risk because it stops ovulation (that’s why women rarely become pregnant while breast-feeding). This theory is supported by the studies that have found that the fewer times a woman ovulates, the lower her risk for breast cancer.

One study concluded that having more children and breast-feeding longer could reduce the risk of breast cancer by half.

Oral contraceptive use
Studies have suggested that women using oral contraceptives have a slightly greater risk of breast cancer than women who have never used them. What matters is the dose of oestrogen in the tablet, and modern pills now contain much lower doses than earlier pills. Women who stopped using oral contraceptives more than 10 years ago do not appear to have any increased breast cancer risk.

Although there may be a small increase in risk in long-term use, the benefits of the pill, which include protection against ovarian cancer, still outweighs the risk. When considering using oral contraceptives, women should discuss the risk factors for breast cancer with their doctors.

Hormone replacement therapy
Long-term use of hormone replacement therapy (HRT) after menopause, particularly oestrogen and progesterone combined, may slightly increase your risk of breast cancer.

If you still have your uterus (womb), doctors generally prescribe oestrogen and progesterone (known as combined HRT). Oestrogen relieves menopausal symptoms and prevents osteoporosis (thinning of the bones that can lead to fractures). But oestrogen can increase the risk of developing cancer of the uterus. Progesterone is added to help prevent this.

If you no longer have your uterus, oestrogen alone can be prescribed. This is commonly known as oestrogen replacement therapy (ERT). This probably does not increase the risk of breast cancer very much, if at all (although it was linked to an increased risk of stroke).

The decision to use HRT 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 woman’s other risk factors for heart disease, breast cancer, osteoporosis, and the severity of her menopausal symptoms.

Alcohol
Use of alcohol is linked to a slightly increased 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 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.

Obesity and high-fat diets
Obesity (being overweight) has been found to be a breast cancer risk factor especially for women after menopause. Although the ovaries produce most of the oestrogen, fat tissue makes a small amount of oestrogen as well. Having more fat tissue can increase your oestrogen 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 inactivity
Evidence is growing that physical inactivity increases the risk of breast cancer. People who regularly exercise have a lower chance of breast cancer. Exercise 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.