Comparing Effects of 1000 IU/day and 50000 IU/Month of Vitamin D Supplementation on 25-Hydroxy Vitamin D Levels of College Students: A Triple-Blind Randomized Controlled Trial

Vitamin D deficiency is a major health concern in the world countries such as Iran. This study was carried out to compare effects of vitamin D supplements in doses of 50000 IU/month and 1000 IU/day on serum 25-hydroxy vitamin D (25(OH)D).

In this triple-blind randomized controlled trial, 90 college students with serum 25(OH)D levels < 30 ng/ml were divided into three major groups of 30 to receive vitamin D3 supplements of either 50000 IU/month and 1000 IU/day or placebos. Intervention was carried out for 12 weeks. Levels of serum 25(OH)D, calcium, phosphorus and parathyroid hormone were assessed as well as weight, waist circumference and blood pressure at the baseline and end of the intervention.

At the end of study, levels of 25(OH)D increased in all groups. This increase was higher in 50000 IU group, compared to 1000 IU group (27.0 ±8.6 instead of 21.2 ng/ml ±9.7, p = 0.01) and in 1000 IU group, compared to placebo group (21.2 ±9.7 instead of 14.0 ng/ml ±11.7, p = 0.04). Parathyroid hormone significantly decreased in all groups with no significant differences between the groups. Intra-group changes were not statistically significant for calcium, phosphorus, weight, waist circumference and blood pressure. Comparison of changes based on 100 IU supplement intake did not show significant differences in 25(OH)D levels between the two supplemental groups. However, decrease of parathyroid hormone was greater in 1000 IU group, compared to 50000 IU group (-2.7 ±4.2 instead of -1.3 pg/ml ±2.1, p = 0.01).

Monthly and daily supplements improved 25(OH)D levels. Based on 100 IU supplement intake, daily supplements caused further decreased parathyroid hormone, which suggested that daily supplementation might include more benefits than monthly supplementaion.