San Antonio - American women aren't going to be able to lower their breast cancer risk to the extent they'd like solely through dietary changes and other lifestyle measures, according to Dr. Walter C. Willett.
"It's pretty clear that we're not going to get a 90% reduction in breast cancer through any feasible modifications of diet and lifestyle alone. We haven't been nearly as successful as we'd like to be. We're going to need other means, probably pharmacologic means," he said in his Brinker Award lecture for scientific distinction in clinical research, presented by the Susan G. Komen Breast Cancer Foundation.
Nevertheless, if American women were to adopt the lifestyle changes for which there is now good evidence of preventative benefit, it looks like the incidence of breast cancer could be reduced by 30% to 40%, added Dr. Willett, professor of medicine, epidemiology, and nutrition at Harvard Medical School, Boston, and director of the second Nurses' Health Study (NHS-II).
The lifestyle modifications that are of benefit are maintenance of high school body weight throughout adulthood - something almost unheard of here but the norm in Japan and other contries with low rates of breast cancer - along with avoidance of prolonged hormone therapy and either refraining from daily alcohol consumption or adding a folate-containing multivitamin, he said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center, where the Brinker Award was presented.
Dr. Willett provided a progress report on the status of a variety of lifestyle factors that have been linked to breast cancer risk:
- Body Weight. A powerful relationship exists between body mass index and risk of postmenopausal breast cancer. This is probably a proxy for estrogen levels in the blood. Among never-users of hormone replacement therapy, there is a nearly fivefold difference in postmenopausal breast cancer rates between women in the highest and lowest estrone sulfate levels.
In contrast, body mass index has an inverse relationship with premenopausal breast cancer risk. In fact, being overweight at age 18 is actually protective against breast cancer for the rest of a woman's life, not just until menopause
- Exercise. While the Nurses' Health Study has documented physical activity's strong preventive effect for coronary heart disease, stroke, colon cancer, and diabetes, it also has shown that exercise in adult life has only a weak inverse relationship to the rate of postmenopausal breast cancer.
- Dietary selenium. Animal studies have suggested that high selenium intake might cut breast cancer risk. Disappointingly, selenium intake as reliably reflected in levels measured in toenail clippings in NHS-II has shown no association with breast cancer.
- Olive oil. Retrospective studies point to a possible association between greater consumption of olive oil and reduced breast cancer risk, but the jury remains out on this issue.
- Alcohol. Dozens of studies have established that women who average even one drink per day have a 10% to 15% increased breast cancer risk, while two to three drinks per day raises the risk by 25%.
- Bruce Jancin
