Diet and breast cancer: a review.

Diet may promote or inhibit human breast cancer through its effects on hormonal systems. In this paper, risk factors with potential dietary components, geographic variations related to diet, experimental studies on diet and mammary tumors, and hormonal hypotheses are reviewed. The associations of early menarche with higher risk, and of early first pregnancy with lower risk suggest that events during teenage years may be determinants of breast cancer. Although data on the association between obesity and mammary cancer are not entirely consistent, it does seem clear that body fatness at menarche and during postmenopausal years may influence hormonal synthesis and metabolism. Published reports based on the Food and Agricultural Organization's food availability data or frequencies of individual foods are inadequate for associating diet with breast cancer incidence or mortality. Also, diets and susceptibility to breast cancer vary among species, and therefore results from rodent experiments should not be extrapolated to humans. Circumstantial evidence suggests that patterns of hormone metabolism in early years of life may be determinants of breast cancer risk. Research concerning the relationship of androgens, prolactin, estrogens, and possibly other hormones to risk factors should be continued. Further, there is a need for data relating dietary factors to hormone synthesis and metabolism. Epidemiological studies among young women in low- and high-risk countries are recommended. Comparisons of diet, body fatness, and hormonal levels could provide further insight about the relationship of diet to breast cancer risk. These same factors should be measured in case-controls studies, along with qualitative estimates of previous diet and possibly weight and height during adolescence. Dietary indices associated with early menarche may be the same as those related to breast cancer. Results of these investigations may provide valuable leads for preventive health programs.