The Effects of Calcium and Vitamin D Supplementation on Blood Glucose and Markers of Inflammation in Non-diabetic Adults

Abstract

Abstract Objective. To compare the effects of combined calcium and vitamin D supplementation vs. placebo on blood glucose and markers of inflammation in non-diabetic adults 65 years of age or older.

Abstract Research Design and Methods. 314 Caucasian adults without diabetes received either 500 mg of calcium citrate and 700 IU of vitamin D₃ or placebos daily for 3 years in a double-blind randomized controlled trial designed for bone-related outcomes. In a post-hoc analysis, fasting plasma glucose (FPG), insulin sensitivity estimated by homeostasis model assessment-insulin resistance (HOMA-IR), plasma C-reactive protein and interleukin-6 were measured at baseline and 3 years.

Abstract Results. The effects of combined calcium-vitamin D supplementation on 3-year change in FPG depended on baseline FPG (p=0.02 for interaction). Therefore, we conducted analyses separately in participants with normal fasting glucose (NFG: FPG <5.6 mmol/L, n=222) and impaired fasting glucose (IFG: FPG 5.6-6.9 mmol/L, n=92) at baseline. Among participants with IFG at baseline those who took combined calcium-vitamin D supplements had a lower rise in FPG at 3 years compared to those on placebo (0.02 mmol/L [0.4 mg/dl] vs. 0.34 mmol/L [6.1 mg/dl] respectively; p=0.042), and a lower increase in HOMA-IR (0.05 vs. 0.91; p=0.031). In the NFG subgroup, there was no difference in the change in FPG or HOMA-IR between the two treatment arms. There were no differences in C-reactive protein or interleukin-6 between the two treatment arms in either subgroup.

Abstract Conclusions. In healthy older adults with impaired fasting glucose, supplementation with calcium and vitamin D may attenuate increases in glycemia and insulin resistance that occur over time. However, our findings should be considered hypothesis generating and need to be confirmed in randomized trials specifically designed for the outcomes of interest. Clinicaltrials.gov identification #NCT00357643.