The efficacy of different vitamin D supplementation delivery methods on serum 25(OH)D: A randomised double-blind placebo trial

Background: The use of vitamin D supplementation has increased due to greater recognition of widespread deficiency.

Aims: There has been little research on the effectiveness of different delivery methods and therefore the aim of was to test the efficacy of different delivery methods on serum 25(OH)D.

Methods: Using a randomised repeated measures double-blind placebo design (registered under ClinicalTrials.gov Identifier no. NCT03463642), changes in serum 25(OH)D over a 4-week period using a capillary spot method were monitored. 62 female participants blindly chose a number related to a supplementation delivery method: pill placebo, pill, oral liquid, oral liquid placebo, Skin oil application (SOA) placebo, SOA plus vitamin D₃ suspension, or SOA plus vitamin D₃ suspension with essential oil enhancer; active vitamin D supplements contained 100,000IU. Participants took their allocated supplements over a 24-hr period with serum 25(OH)D retested 4 weeks later. Liquid chromatography-tandem mass spectrometry method was applied to dried blood spot samples by an independent laboratory.

Results: ANCOVA reported a significant difference between the groups (F_1,6 = 146.68; p < 0.001, eta² = 0.51). Separate analysis within the delivery methods (pill, SOA, oral liquid) indicated significant differences between the active and placebo supplementation groups (p < 0.01). Post hoc analysis of absolute changes indicated vit D pill and SOA + vit D + essential oil had significant increases (p < 0.05) in serum 25(OH)D compared to all other interventions with no significant difference between them.

Conclusions: In human participants vitamin D oral pill has the greatest effect on serum 25(OH)D levels. Skin oil application delivery of vitamin D using a penetrator enhancer has also been shown to be an effective method of delivery.