Background: Vitamin D deficiency is a common problem worldwide. Several studies have shown an association between vitamin D deficiency and the increased risk of metabolic syndrome. No previous study has compared the efficacy and safety of ergocalciferol at 40,000 versus 20,000 IU/week in patients with metabolic syndrome. 

Objective: To evaluate the efficacy of ergocalciferol supplementation on serum 25-hydroxyvitamin D [25(OH)D] concentrations and to examine safety parameters in metabolic syndrome patients. 

Setting: Outpatient department of Phramongkutklao Hospital, Bangkok, Thailand. 

Method: A randomized, double-blinded, parallel study was conducted in metabolic syndrome patients with vitamin D deficiency [25(OH)D <20 ng/mL]. Ninety patients were randomly assigned into three groups of 30 patients each. Group 1 was given two capsules of placebo/week, group 2 was given ergocalciferol 20,000 IU/week, and group 3 was given ergocalciferol 40,000 IU/week for 8 weeks. 

Main outcome measure: serum 25(OH)D concentrations, serum calcium, safety, and corrected QT (QTc) interval. 

Results: Of the 90 patients enrolled, 84 patients completed the study. At the end of the study, the mean serum 25(OH)D in groups 2 and 3 significantly increased from the baseline (15.1 and 14.3 to 26.8 and 30.0 ng/mL, respectively). The increase in serum 25(OH)D in groups 2 and 3 were comparable and significantly greater than that of the placebo group. The percentage number of patients achieving normal vitamin D levels in groups 1, 2 and 3 were 3.3, 33.3, and 60.0 %, respectively, which were significantly different between groups (p < 0.001). Adverse reactions in both ergocalciferol treatment groups were not different from the placebo group (p > 0.05). Serum calcium levels did not change within and between groups of treatment. No significant change in QTc was observed in any patient. 

Conclusions: Both 20,000 and 40,000 IU/week of ergocalciferol supplementation for 8 weeks were able to increase serum 25(OH)D concentrations significantly. However, more patients in the ergocalciferol 40,000 IU/week treatment group achieved a normal serum 25(OH)D level than in the group which received 20,000 IU/week. Clinicians would have informed of choosing the dosing regimen of ergocalciferol in metabolic syndrome patients.