Effect of vitamin D3 supplementation on glycated hemoglobin (HbA1c), fructosamine, serum lipids, and body mass index: a randomized, doubleblinded, placebo-controlled trial among healthy immigrants living in Norway

Abstract

Objective Despite the suggested role of vitamin D in the prevention of diabetes and cardiovascular disease or its risk factors, the evidence is not consistent and there is a paucity of randomized controlled trials in this field. We aimed to investigate the effect of 16-week daily vitamin D3 supplementation on glycated hemoglobin (HbA1c), fructosamine, body mass index (BMI), and serum lipids. Design Double-blind, randomized, placebo-controlled trial. Setting Immigrant community centers in Oslo, Norway. Participants 251 healthy adults aged 18–50 years with a non-Western immigrant background. All participants performed the baseline test and 215 (86%) returned to the follow-up test. Intervention 16 weeks of daily oral supplementation with either 10 µg vitamin D3, 25 µg vitamin D3, or placebo. Main outcome measures Difference in absolute change during the 16-week intervention between the intervention groups combined (10 or 25 µg of vitamin D3/day) and placebo, in HbA1c, fructosamine, serum lipids (total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides), and BMI. Results A total of 215 (86%) participants completed the study. Serum 25-hydroxyvitamin D increased from 29 nmol/L at baseline to 49 nmol/L after intervention, with little change in the placebo group. However, there was no difference in change of HbA1c between those receiving vitamin D3 compared with placebo (mean difference: 0.01% (95% CI -0.04 to 0.06, p=0.7)). Neither did the vitamin D3 supplementation have any effect on the other end points: fructosamine, serum lipids, and BMI. Conclusions 16-week vitamin D3 supplementation to healthy immigrants from South Asia, the Middle East, or Africa and now living in Norway with low vitamin D status did not improve HbA1c, fructosamine, lipid profiles, or BMI. An updated meta-analysis of similar published trials showed that our results were generally consistent with those of other studies.