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

This is an accepted manuscript of an article published by Elsevier in Clinical Nutrition on 05/06/2020. The published version can be accessed here: https://doi.org/10.1016/j.clnu.2020.05.040 The accepted version of the publication may differ from the final published version.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 (F1,6=146.68; p<0.001, eta2 =.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