Dietary calcium intake and risk of type 2 diabetes: possible confounding by magnesium

This study examined the association of dietary calcium intake with incident type 2 diabetes by a meta-analysis and explored the potential confounding by magnesium. Potential studies were identified by searching the PubMed database in September 2011. Prospective cohort studies that reported relative risks (RR) with 95% confidence intervals (CI) of type 2 diabetes for dietary calcium intake were selected. Results were combined using either a fixed-or random-effects model. Six prospective cohort studies comprising 264 268 participants and 11 225 reported cases were included. All combined random-effects meta-analysis yielded a significant pooled RR of 0.85 (95% CI 0.75-0.97). However, a sensitivity analysis limited to four studies with control for magnesium yielded an attenuated, nonsignificant pooled RR of 0.94 (95% CI 0.85-1.05). In conclusion, dietary calcium intake was not independently associated with risk of type 2 diabetes. The inverse association in prior observational studies may be partially confounded by magnesium intake.