High vegetable fat intake in teen years may reduce breast Ca risk: nurses' health study data.(Gynecology)

SAN ANTONIO -- Dietary fat consumption during adolescence--but not in midlife--may be an important modifiable risk factor for breast cancer, according to Dr. Walter C. Willett.

Three separate analyses of data from the first and second Nurses' Health Study (NHS), two of them so recent they haven't yet been pub fished, suggest greater consumption of vegetable fat during high school may protect against development of breast cancer decades later, conferring up to a 39% reduction in relative risk, according to Dr. Willett, professor of medicine, epidemiology, and nutrition at Harvard Medical School, Boston, and director of NHS II.

NHS and NHS II are prospective studies focusing on the role of diet, exercise, and other lifestyle factors in the evolution of breast cancer, cardiovascular disease, and other major diseases in women. The two studies constitute an unusual resource in part because of their sheer size, which generates end points in such quantity that hypotheses can be tested relatively rapidly. The NHS, started in 1976, involves 121,700 nurses, while NHS II, established in 1989, involves a cohort of 116,000 younger nurses from whom stored blood samples as well as 80,000 toenail clippings have been obtained, he said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.

The studies are also unusual in that they involve multiple dietary assessments over the years, providing a more realistic picture of dietary changes over time than are available in most other epidemiologic studies, where diet is assessed only once. Perhaps because NHS and NHS II involve health professionals, they also have an unusually low dropout rate, he explained in his Brinker Award Lecture for scientific distinction in clinical research presented by the Susan G. Komen Breast Cancer Foundation.

The story of the diet/breast cancer link has grown more complicated over time. Two decades ago the conventional wisdom among epidemiologists was that greater dietary fat intake accounted for most of the increased incidence of breast cancer in the Unit ed States and other western countries relative to, say, Japan.

But because the NHS--the 800pound gorilla of epidemiologic researeh--failed to show even a hint of an association between fat intake and breast cancer risk, an international pooling project was organized. This project, which drew the principal investigators of all the large prospective studies of diet and breast cancer worldwide, involved more than 300,000 women and 5,000 incident cases of breast cancer. Like the NHS, it failed to show any association between increased dietary fat and higher risk.

Moreover, the 20-year NHS follow-up now in progress, featuring roughly 4,500 incident cases of breast cancer, continues to show no association between dietary fat and breast cancer risk, Dr. Willett continued.