The Relationship between Serum Calcium Level and Early-phase Insulin Secretion in Normoglycemic and Pre-diabetic Individuals

Introduction: Type 2 diabetes mellitus (T2DM) is linked to altered calcium metabolism. However, little is known about the relationship between serum calcium levels and early-phase insulin secretion in subjects with normoglycemic tolerance (NGT) or prediabetes (preDM). Methods: In this gender-separated crosssectional study, 352 subjects with NGT (215 men and 137 women; age: 48.8 +/- 9.1 years and 51.6 +/- 6.7 years, respectively) and 316 subjects with preDM (231 men and 85 women; age: 52.5 +/- 8.6 years and 54.2 +/- 8.0 years, respectively) were examined. Following a 75-g oral glucose tolerance test, early-phase insulin secretion was estimated using the insulinogenic index (IGI) [Delta Insulin((30-0 min))/Delta Glucose((30-0 min))]. Results: Simple linear regression analysis showed that IGI was positively correlated with serum calcium and albumin-adjusted calcium levels in men with NGT and preDM. However, IGI was not correlated with calcium levels in women with NGT and preDM. Multivariate linear regression analysis of men with NGT revealed that the albumin-adjusted calcium level was the major predictor of IGI, responsible for 5.1 % of its variation (P = 0.003). In addition, in men with preDM, the albumin-adjusted calcium level was one of the predictors of IGI, responsible for 3.8 % of its variation (P = 0.004). These associations were independent of age, BMI, and HbA1c. Conclusions: In non-diabetic Japanese men, serum calcium levels significantly correlate with early-phase insulin secretion. Serum calcium levels may be an independent predictor of beta-cell function in men.