Serum Calcium and Diabetes: The Atherosclerosis Risk in Communities (ARIC) Study

Introduction: Non-skeletal calcium serves a variety of functions. Pertinent to diabetes, an influx of calcium through calcium channels into pancreatic β-cells is required for insulin secretion. Previous cohort studies exploring the association between serum calcium and diabetes have not accounted for 25-hydroxyvitamin D [25(OH)D], or parathyroid hormone (PTH), and have had limited racial/ethnic diversity. Hypothesis: We hypothesized that serum calcium concentration would be positively and independently associated with diabetes incidence. Methods: A total of 12,800 black and white ARIC study participants without diabetes at baseline (visit 1, 1987-1989) were followed for incident diabetes. Serum calcium was measured at baseline, and corrected for serum albumin. Levels of 25(OH)D and PTH were assessed at visit 2. Diabetes was identified by glucose levels, self-report or medication use at any of three follow-up exams (each approximately 3 years apart). Multivariate Cox proportional hazards regression models were used to estimate hazard ratios and 95% confidence intervals. Results: Mean age was 54, 23% were black and 56% female, mean serum calcium concentration was 9.87 mg/dL overall, and 9.96 mg/dL in blacks, and 9.84 in whites. During a median of 9 years of follow-up, 1516 cases of diabetes were identified. Baseline serum calcium was positively and independently associated with incident diabetes after adjustment for demographic and lifestyle characteristics (Table). This association was largely unchanged with further adjustment for biomarkers that may lie on the metabolic pathway (i.e. 25(OH)D, PTH, phosphorus). While there was not a significant race interaction (p-interaction u003e 0.25 in all models), the calcium-diabetes association was somewhat stronger among blacks than whites (Table). Conclusions: Consistent with prior studies, elevated serum calcium was associated with greater risk of type 2 diabetes. Further research is needed to understand the role calcium plays in the pathogenesis of diabetes.