ABSTRACT
Vitamin D deficiency is highly prevalent among non-western immigrants in The Netherlands and associated with poor physical performance. The aim of this study was to assess the effect of vitamin D supplementation on physical performance, exercise capacity, and daily physical activity in vitamin D-deficient, overweight non-western immigrants. A randomized double-blind, placebo-controlled trial was conducted to assess the effect of vitamin D on physical performance. A total of 130 participants were included. Eligibility criteria included overweight (BMI >27âkg/m(2)), 25-hydroxy vitamin D (25(OH)D) ≤50ânmol/l, and an age range of 20-65 years. The intervention group received 1200âIU vitamin D3 daily for 4 months; the control group received placebo. Both groups received 500âmg calcium daily. Outcome measures included physical performance (physical performance score), exercise capacity (a 6-min walk test (6-MWT)), and daily physical activity (questionnaire and accelerometer). There was no significant effect on physical performance, exercise capacity, or physical activity in the intention to treat analysis. In an explorative post hoc analysis restricted to participants reaching a serum 25(OH)D concentration of >60ânmol/l after intervention, there was an improvement of 19âm in the 6-MWT compared with the control group (P=0.053). Moderate dose vitamin D supplementation did not significantly improve physical performance, exercise capacity, or physical activity. However, when 25(OH)D concentrations reached >60ânmol/l after intervention, there was a borderline significant improvement in exercise capacity. Although the clinical relevance is not clear, this is a promising result, as all participants were overweight and did not improve their overall activity levels.
ABSTRACT
BACKGROUND: Low serum 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with insulin resistance, the metabolic syndrome, and type 2 diabetes. Because many non-Western immigrants in the Netherlands are vitamin D deficient, obese, and at high risk of diabetes, vitamin D supplementation may contribute to prevent diabetes and insulin resistance. OBJECTIVE: We examined the effect of vitamin D supplementation on insulin sensitivity and ß cell function in overweight, vitamin D-deficient, non-Western immigrants at high risk of diabetes. DESIGN: The study was a 16-wk, randomized, placebo-controlled trial. A total of 130 non-Western immigrants with prediabetes (fasting glucose concentration >5.5 mmol/L or random glucose concentration from 7.8 to 11.1 mmol/L) and vitamin D deficiency (serum 25[OH]D concentration <50 nmol/L) were randomly assigned after stratification by sex to receive either cholecalciferol (1200 IU/d) or a placebo for 16 wk. All participants received 500 mg Ca/d as calcium carbonate. The primary outcome was the difference in the area under the curve of insulin and glucose after a 75-g oral-glucose-tolerance test after 4 mo of treatment. Secondary outcomes were insulin-sensitivity variables, ß cell-function variables, and metabolic syndrome. RESULTS: Mean serum 25(OH)D concentrations increased significantly in the vitamin D compared with placebo groups. After 4 mo of therapy, the mean between-group difference was 38 nmol/L (95% CI: 32.1, 43.9 nmol/L; P < 0.001). There was no significant effect on insulin sensitivity and ß cell function. In a post hoc analysis, when patients with diabetes at baseline were excluded, a significant increase in the insulinogenic index was observed in participants who obtained a 25(OH)D concentration ≥60 nmol/L (P = 0.040). CONCLUSIONS: Vitamin D supplementation in non-Western vitamin D-deficient immigrants with prediabetes did not improve insulin sensitivity or ß cell function or change the incidence of metabolic syndrome. However, after the exclusion of diabetic subjects, an improvement in the insulinogenic index was observed in participants who obtained a 25(OH)D concentration ≥60 nmol/L. This trial was registered at trialregister.nl as NTR1827.
