Dairy Product Intake and Risk of Type 2 Diabetes in EPIC-InterAct: A Mendelian Randomization Study

OBJECTIVE To estimate the causal association between intake of dairy products and incident type 2 diabetes. RESEARCH DESIGN AND METHODS The analysis included 21,820 European individuals (9,686 diabetes cases) of the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study. Participants were genotyped, and rs4988235 (LCT-12910C>T), a single nucleotide polymorphism (SNP) for lactase persistence (LP) that enables digestion of dairy sugar, i.e., lactose, was imputed. Baseline dietary intakes were assessed with diet questionnaires. We investigated the associations between imputed SNP dosage for rs4988235 and intake of dairy products and other foods through linear regression. Mendelian randomization (MR) estimates for the milk-diabetes relationship were obtained through a two-stage least squares regression. RESULTS Each additional LP allele was associated with a higher intake of milk (beta 17.1 g/day, 95% CI 10.6-23.6) and milk beverages (beta 2.8 g/day, 95% CI 1.0-4.5) but not with intake of other dairy products. Other dietary intakes associated with rs4988235 included fruits (beta -7.0 g/day, 95% CI -12.4 to -1.7 per additional LP allele), nonalcoholic beverages (beta -18.0 g/day, 95% CI -34.4 to -1.6), and wine (beta -4.8 g/day, 95% CI -9.1 to -0.6). In instrumental variable analysis, LP-associated milk intake was not associated with diabetes (hazard ratio(per 15 g/day) 0.99, 95% CI 0.93-1.05). CONCLUSIONS rs4988235 was associated with milk intake but not with intake of other dairy products. This MR study does not suggest that milk intake is associated with diabetes, which is consistent with previous observational and genetic associations. LP may be associated with intake of other foods as well, but owing to the modest associations, we consider it unlikely that this caused the observed null result.