Although all of the genetic and environmental factors are important to consider, the overwhelming evidence is that breast cancer is related to lifestyle. The following paragraphs outline the negative impact and positive impact on breast cancer of several common lifestyle related issues.
Post-menopausal Obesity Increases Risk: Despite the evidence on the protective effect of pre-menopausal obesity on pre-menopausal breast cancer, the evidence that obesity increases the risk of post-menopausal breast cancer is very clear and not debatable. Some have suggested that tumors are harder to find by physical exam and mammography in obese women. This theory has largely been disproved in studies looking at mammography sensitivity and specificity, as well as studies looking at breast exam diagnosis in obese patients. If the correlation between obesity and cancer mortality is entirely causal, some scientists even estimate that an overweight condition and/or obesity now may account for one in seven of cancer deaths in men and one in five in women in the US.
High Fat Diet and Breast Cancer: Although breast cancer publications and the media have promulgated the idea that a low fat diet reduces cancer risk, most clinical trials have not successfully demonstrated this direct beneficial effect. There have been several methodological explanations for this failure. However, the reverse observation that a high fat diet increases breast cancer risk remains solid. For example, a large study funded by the National Institute of Health looked at 188,736 postmenopausal women and fat intake, based on both “food frequency questionnaires” and “24-hour dietary recall questionnaires”. With the food frequency questionnaires, researchers found that women who got 40% of their calories from fat had about a 15% increased risk of developing breast cancer compared with women who got 20% of their calories from fat. With the “24-hour dietary recall questionaire”, they found a 32% increased risk of breast cancer among women with a high level of fat in their diet.
Alcohol: Based on scientific evidence, exposure to alcohol is associated with increased breast cancer risk in a dose-dependent fashion. Even less than one drink/day on a daily basis can be associated with up to a 30% increase in breast cancer mortality among postmenopausal women compared to non-drinkers. The risk may increase by 7% for each drink per day. Studies have shown that stopping alcohol use may reverse this risk.
Exercise: Exercise has been consistently linked with reduced breast cancer risk. A regimen of approximately 30 minutes per day of moderate-intensity exercise should be adequate, and perhaps even one to two hours per week is enough to be helpful. It appears that longer duration and greater intensity of activity may bring even more health benefits.
Supplements: Americans spend billions of dollars on vitamins and mineral supplements. Recent large studies, however, have demonstrated that these pills and capsules do not decrease the risk of many types of cancer. One explanation is that as long as one is not deficient of any particular vitamin or mineral, ingestion of super-normal levels of supplements does not help. Many women have low levels of vitamin D, and some data have shown that increasing its level (whether in a pill or by sun exposure) can protect somewhat against future breast cancer. In our opinion, botanical dietary supplements derived from green tea extracts represent a potentially widely available method for reducing the risk of breast cancer. Next to water, tea is the most widely consumed beverage in the world, and its ingestion in reasonable doses is considered safe. Many population observation reports have shown that green tea may decrease the risk of breast cancer.