Dairy products and breast cancer: the estrogen, and bGH hypothesis IGF-I,

Research on the role of dietary factors in breast cancer causation has focused predominantly on fat intake. While some studies have examined associations between breast cancer rates and consumption of whole milk, there has been less attention given to dairy products in general. Dairy products contain both hormones and growth factors, in addition to fat and various chemical contaminants, that have been implicated in the proliferation of human breast cancer cells. This literature review evaluates the epidemiological and mechanistic evidence linking dairy consumption with breast cancer risk. Epidemiological evidence Epidemiological studies have indicated a positive correlation between dairy product consumption and breast cancer risk (1-12). Two studies have specifically examined breast cancer mortality and frequency of consumption of various milk products, concluding that cancer risk was associated with milk intake (1,2). Stocks found low death rates for breast cancer where dairy product consumption was low and intake of other fats was high. Other studies found a dose-dependent increase in breast cancer risk among women who consumed milk (especially whole milk) and/or cheese (3-7). Further studies reported a relative risk (RR) coefficient that was more statistically significant than that for meat (8-10). When La Veccia adjusted the RR coefficients for age at first birth and economic variables, the risk factors for milk and cheese were the only dietary variables to remain significantly positive (8). Maruchi et al examined the incidence of breast cancer in Japan, and found a significant increase in both the consumption of dairy products and occurrence of breast cancer in urban areas (P < 0.001), where the average intake of the other fatty foods, including meat, was at or below average (9). Talamini et al also found the relative risk factors for breast cancer to increase with the amount of dairy products consumed (1.0-3.4, P < 0.001); however, the trend was not as evident in values for meat consumption (10). Several studies examined the relative risks of consuming whole versus low-fat milk (11-13). Toniolo (1989) and Ewertz (1990) concluded that breast cancer risk was significantly related to increasing consumption or whole milk, as well as frequent intake of low-fat or skim milk (11-12). In Ewertz's study, the RRs decreased when adjusted for total fat intake, with the exception of the RR for low-fat milk. In a study of Seventh-Day Adventists, Phillips found a positive correlation between dairy products other than Date received 6 May 1996 Date accepted 3 July 1996