Effect of vitamin D3 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

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.

Trial registration number: NCT01263288.

Keywords: Body Mass Index; Glycated Hemoglobin; Serum Lipids; Vitamin D.

Figures

Figure 1

Flow chart of recruitment, randomization, and follow-up.

Figure 2

Subgroup analysis. Effect of vitamin D supplementation on outcome variables in subgroups defined by baseline levels of the respective outcome variables. Effect estimates for each outcome variable are difference in change from baseline to 16 weeks between the combined intervention groups (10 or 25 µg) and the placebo group. Within each subgroup, the effect estimate was adjusted for the baseline level of the respective outcome variables (baseline value entered as a continuous variable in the regression model).