Predictors of serum 25(Oh)D increase following bimonthly supplementation with 100,000IU vitamin D in healthy, men aged 25-65 years

Abstract

Vitamin D replenishment therapy typically entails standard dosages, but related increases in serum 25(OH)D levels vary between individuals. This study was aimed to identify factors that affect the efficacy of vitamin D supplementation.

Subjects and methods: 79 healthy men aged 25-65 with 25(OH)D<20ng/ml participated in a vitamin D supplementation study. All participants received 100,000IU vitamin D bimonthly, e.g., 1666IU/day. Personal and demographic information, physical activity and sun-exposure questionnaires were completed by the participants. Weight, height, and waist circumference were recorded. Serum calcium, creatinine, 25(OH)D, PTH, lipid profile, and liver-enzyme levels were assessed. All measurements were repeated after 6 and 12 months. The difference between baseline serum 25(OH)D and 12-month measurements was calculated (delta). Linear regression was performed to identify predictors for increases in 25(OH)D levels.

Results: Mean serum 25(OH)D level increases according to BMI were 12.6±5.29ng/ml for BMI≤25, 10.12±4.95ng/ml for 25<BMI<30, and only 6.39± 5.33ng/ml for BMI>30, which differed significantly from the other BMI categories (p=0.003). In a regression model to predict 25(OH)D increase, BMI was the main predictor (p<0.001), explaining 21.6% of the variance in serum 25(OH)D (inverse association). Age, sun-exposure, serum cholesterol, physical-activity, baseline 25(OH)D levels and seasonality were insignificant. The full model explained 27.9% of the variance in serum 25(OH)D.

Conclusion: This study's main findings are that BMI affect vitamin D response in healthy men. Quantitative supplementation adjustments may be warranted in obese men, for whom the dose may need to be doubled. This article is part of a special issue entitled '16th Vitamin D Workshop'.

Keywords: 25(OH)D; Age; BMI; Men; Season; Sun-exposure; Supplementation; Vitamin D.