Bovine milk fat and cancer risk: A double-edged sword?

Among the many macro- and micronutrients contained in cow's milk, one of the most important is the lipid fraction. While the nutritional and physiological benefits of milk consumption after the first years of life are the subject of some debate, there also appear to be conflicting views on the health aspects of the milk lipids, including their involvement in cancer. Positive in vitro and/or in vivo data on growth-inhibiting or cytotoxic effects are available for lipid components of milk such as sphingomyelins and their degradation products or various hydroxy fatty acids. Isomers of linoleic acid and branched-chain fatty acids have also been shown to have anticarcinogenic potential in animal models by inducing apoptosis. On the other hand, there is evidence of an association between increased cancer mortality and the consumption of high-fat milk, which contradicts the tumor-protecting effects observed in vitro and in vivo. Consumption of high-fat dairy products appears to be associated with an increased risk of developing types of cancer compared to low-fat dairy or other topical soy-based alternatives. There are ambiguous results for an anticarcinogenic effect of various lipid constituents of cow's milk as well as for an association between general milk fat consumption and the occurrence especially of breast, colorectal, and prostate tumors. Whether the effects observed in epidemiological studies can be attributed to milk lipids or whether the promising preclinical data on their anti-cancer efficacy can be transferred to humans remains unclear at present, therefore this review summarizes the latest findings.