Can Milk Do Harm?

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Science Translational Medicine  29 Oct 2014:
Vol. 6, Issue 260, pp. 260ec185
DOI: 10.1126/scitranslmed.aaa1239

For decades, the identification of dietary factors contributing to cancer risk has captured the attention and efforts of researchers, health care providers, and the general public. Frequently cited associations include colorectal malignancies among populations consuming diets high in red meat and low in fruits and vegetables; gastric cancer and high-salt diets; and high-fat diets predisposing to breast cancer.

Whether consumption of dairy products specifically heightens cancer risk remains unclear. Epidemiologic studies have reported inconsistent results. Potential drivers of this association include high amounts of saturated fats, as well as growth factors such as insulin-like growth factor 1.

Taking a new approach to this question, Ji et al. capitalize on Mendelian randomization by examining the incidence of various malignancies among individuals with lactose intolerance. Using several Swedish Registers linked to the Swedish Cancer Registry, they identified almost 23,000 persons with lactose intolerance. Compared with the general population, their risks of lung [standardized incidence ratio (SIR) = 0.55], breast (SIR = 0.79), and ovarian (SIR = 0.55) cancers were significantly decreased. However, the incidences of cancer in the siblings and parents of individuals with lactose intolerance were similar to those in the general population.

The investigators conclude that this dietary pattern may protect against cancer risk. Whether this is due to avoidance of dairy products, caloric restriction, or protective effects of plant (such as soy or rice), milk consumption is not clear. Furthermore, the possibility that genetic variants in the lactose-intolerant population confound expression of other genes through linkage disequilibrium must be considered. Although this report does not settle the long-term debate over the association between dairy products and cancer, its approach is sure to inspire further investigation into this important area.

J. Ji et al., Lactose intolerance and risk of lung, breast and ovarian cancers: Aetiological clues from a population-based study in Sweden. Brit. J. Cancer 10.1038/bjc.2014.544 (2014). [Abstract]

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