Effect of vitamin D(3) supplementation on glycated hemoglobin (HbA1c), fructosamine, serum lipids, and body mass index: a randomized, double-blinded, placebo-controlled trial among healthy immigrants living in Norway

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 D(3) 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 D(3), 25 μg vitamin D(3,) 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 D(3)/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 D(3) compared with placebo (mean difference: 0.01% (95% CI −0.04 to 0.06, p=0.7)). Neither did the vitamin D(3) supplementation have any effect on the other end points: fructosamine, serum lipids, and BMI. CONCLUSIONS: 16-week vitamin D(3) 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. TRIAL REGISTRATION NUMBER: NCT01263288.