Physical activity

Physical activity

Evidence is growing that physical activity in the form of exercise reduces breast cancer
risk. The main question is how much exercise is needed. In one study from the Women'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.
Factors with uncertain, controversial, or unproven effect on
breast cancer risk
Diet and vitamin intake
Many studies have looked for a link between what women eat and breast cancer risk, but
so far the results have been conflicting. Some studies have indicated that diet may play a
role, while others found no evidence that diet influences breast cancer risk. Studies have
looked at the amount of fat in the diet, intake of fruits and vegetables, and intake of meat.
No clear link to breast cancer risk was found.
Studies have also looked at vitamin levels, again with inconsistent results. Some studies
actually found an increased risk of breast cancer in women with higher levels of certain
nutrients. So far, no study has shown that taking vitamins reduces breast cancer risk. This
is not to say that there is no point in eating a healthy diet. A diet low in fat, low in red
meat and processed meat, and high in fruits and vegetables might have other health
benefits.
Most studies have 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. But many
studies of women in the United States have not linked breast cancer risk to dietary fat
intake. Researchers are still not sure how to explain this apparent disagreement. It may be
at least partly due to the effect of diet on body weight (see below). Also, studies
comparing diet and breast cancer risk in different countries are complicated by other
differences (like activity level, intake of other nutrients, and genetic factors) that might
also affect breast cancer risk.
More research is needed to understand the effect of the types of fat eaten on breast cancer
risk. But it is clear that calories do count, and fat is a major source of calories. High-fat
diets can lead to being overweight or obese, which is a breast cancer risk factor. 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.