Abstract
Objectives
Vitamin D insufficiency is a global health concern that affects nearly 50% of the population worldwide. Growing demand for vegan/vegetarian products has aroused interest in the plant-sourced D2 form for use in dietary supplements. However, vitamin D2’s ability to raise serum 25(OH)D levels in relation to D3 among existing scientific literature is inconclusive. This study sought to compare vitamin D2 to D3 in increasing serum 25(OH)D levels in order to better understand the relative potency and dosage required to address vitamin D insufficiencies.
Methods
PubMed and Embase databases were searched through July of 2018. Randomized controlled trials comparing D2 and D3 supplementation of equivalent dosages and the resulting increase in serum 25(OH)D levels in adults were eligible for this meta-analysis. A meta regression was conducted to compare the impact of both vitamin D forms on serum 25(OH)D levels. The outcome variable evaluated was the serum 25(OH)D levels.
Results
Nine RCTs (n = 628) with vitamin D dose ranging from 10 mcg per day to 1250 mcg per week, and an intervention duration from 2 to 16 weeks were eligible. Subjects included healthy adults as well as those with chronic kidney disease. There was substantial heterogeneity among the studies (I2 = 78.07%). The meta-regression showed vitamin D supplementation regardless of form was effective in raising serum 25(OH)D levels (P < 0.0001). The mean effect size expressed as the standardized mean difference (SMD) from baseline serum 25(OH)D levels was 1.16 [95% CI: 0.83, 1.49] for D2 and 1.52 [95% CI: 0.99, 2.04] for D3. While there was a trend of greater increase caused by D3 numerically, the difference between D2 and D3 was not statistically significant. When duration and frequency of supplementation were examined, similar trends of non-significant greater increases for D3 relative to D2 were observed.
Conclusions
This research shows both vitamin D2 and D3 supplementation can significantly increase serum 25(OH)D levels. Though the results did not reach statistical significance, there is a consistent trend of vitamin D3 offering additional effectiveness relative to D2. The high heterogeneity across studies and small sample size likely contributed to the non-significant results and limited the ability to identify a quantitative relative potency that can be used for a D2 dosage recommendation.
Funding Sources
None.