Background: Currently, there is a lack of clarity in the literature as to whether there is a definitive difference between the effects of vitamins D 2 and D 3 in the raising of serum 25-hydroxyvitamin D [25(OH)D].
Objective: The objective of this article was to report a systematic review and meta-analysis of randomized controlled trials (RCTs) that have directly compared the effects of vitamin D 2 and vitamin D 3 on serum 25(OH)D concentrations in humans.
Design: The ISI Web of Knowledge (January 1966 to July 2011) database was searched electronically for all relevant studies in adults that directly compared vitamin D 3 with vitamin D 2. The Cochrane Clinical Trials Registry, International Standard Randomized Controlled Trials Number register, and clinicaltrials.gov were also searched for any unpublished trials.
Results: A meta-analysis of RCTs indicated that supplementation with vitamin D 3 had a significant and positive effect in the raising of serum 25(OH)D concentrations compared with the effect of vitamin D 2 ( P = 0.001). When the frequency of dosage administration was compared, there was a significant response for vitamin D 3 when given as a bolus dose ( P = 0.0002) compared with administration of vitamin D 2, but the effect was lost with daily supplementation.
Conclusions: This meta-analysis indicates that vitamin D 3 is more efficacious at raising serum 25(OH)D concentrations than is vitamin D 2, and thus vitamin D 3 could potentially become the preferred choice for supplementation. However, additional research is required to examine the metabolic pathways involved in oral and intramuscular administration of vitamin D and the effects across age, sex, and ethnicity, which this review was unable to verify.