Elevated serum levels of calcium are associated with an increased risk of incident type 2 diabetes mellitus (T2DM), according to a new study. As part of the Atherosclerosis Risk in Communities (ARIC) study, 12,800 participants who were free of T2DM at baseline were followed up for a median of 8.8 years; serum levels of calcium were measured at baseline. Individuals in the highest calcium quintile were at higher risk of incident T2DM than those in the lowest quintile after adjusting for demographic and lifestyle factors (HR 1.34, 95% CI 1.14–1.57); adjustment for levels of 25-hydroxyvitamin D and parathyroid hormone did not affect the association.