Effects of calcium–vitamin D co-supplementation on metabolic profiles in vitamin D insufficient people with type 2 diabetes: A randomised controlled clinical trial

Aims/hypothesis This study was performed to assess the effects of vitamin D and calcium supplementation on the metabolic profiles of vitamin D insufficient persons with type 2 diabetes. Methods In a parallel designed randomised placebocontrolled clinical trial, a total of 118 non-smoker individuals with type 2 diabetes and insufficient 25-hydroxyvitamin D, aged >30 years, were recruited from the Isfahan Endocrine andMetabolism Research Centre. Participants were randomly assigned to four groups receiving: (1) 50,000 U/week vitamin D + calcium placebo; (2) 1,000 mg/day calcium + vitamin D placebo; (3) 50,000 U/week vitamin D + 1,000 mg/day calcium; or (4) vitamin D placebo + calcium placebo for 8 weeks. A study technician carried out the random allocations using a random numbers table. All investigators, participants and laboratory technicians were blinded to the random assignments. All participants provided 3 days of dietary records and 3 days of physical activity records throughout the intervention. Blood samples were taken to quantify glycaemic and lipid profiles at study baseline and after 8 weeks of intervention. Results 30 participants were randomised in each group. During the intervention, one participant from the calciumgroup and one from the vitamin D group were excluded because of personal problems. Calcium–vitamin D co-supplementation resulted in reduced serum insulin (changes from baseline: −14.8±3.9 pmol/l, p=0.01), HbA_1c[−0.70±0.19% (−8.0±0.4 mmol/mol), p=0.02], HOMA-IR (−0.46±0.20, p=0.001), LDL-cholesterol (−10.36±0.10 mmol/l, p=0.04) and total/HDL-cholesterol levels (−0.91±0.16, p=0.03) compared with other groups. We found a significant increase in QUICKI (0.025±0.01, p=0.004), HOMA of beta cell function (HOMA-B; 11.8±12.17, p=0.001) and HDL-cholesterol (0.46±0.05 mmol/l, p=0.03) in the calcium–vitamin D group compared with others. Conclusions/interpretation Joint calcium and vitamin D supplementation might improve the glycaemic status and lipid profiles of vitamin D insufficient people with type 2 diabetes. Trial registration: ClinicalTrials.gov NCT01662193 Funding: Clinical Research Council, Isfahan University of Medical Sciences, Isfahan, Iran