Lactase persistence and bitter taste response: instrumental variables and mendelian randomization in epidemiologic studies of dietary factors and cancer risk.

Consumption of dairy products seems to increase the risk of cancer at several sites, while intake of cruciferous vegetables could have protective effects. However, these dietary intakes are subject to measurement error, and associations with cancer could be due to confounders. Mendelian randomization has been suggested as a way to overcome confounding by exploiting the random allocation of alleles from parents to offspring. In mid-2006, the authors conducted a study of allele frequencies for the lactase (LCT) and taste receptor, type 2, member 38 (TAS2R38) genes, including 634 volunteers recruited (1992-1998) from the Italian branch of the European Prospective Investigation into Cancer and Nutrition. The authors hypothesized that there would be a lower milk intake among carriers of the LCT CC genotype and a different intake of cruciferous vegetables among carriers of the TAS2R38 variant. Overall, the frequency of the LCT T allele was higher in northern Italy than in southern Italy. Food intake was associated with gene variants. An association was evident for ice cream and LCT variants (p = 0.004); less so for milk intake. In addition, the TAS2R38 variant showed a geographic gradient and an association with cruciferous vegetable intake. These results suggest that the LCT and TAS2R38 variants are good candidates for Mendelian randomization studies of cancer and other health outcomes.