Serum 25-hydroxyvitamin D response to vitamin D supplementation using different lipid delivery systems in middle-aged and older adults: A randomised controlled trial.

Food fortification improves vitamin D intakes but is not yet mandated in many countries. Combining vitamin D with different dietary lipids altered vitamin D absorption in in-vitro and postprandial studies. This randomised, placebo-controlled trial examined the effect of the lipid composition of a vitamin D fortified dairy drink on change in 25-hydroxyvitamin D (25(OH)D) concentrations. Sixty-three healthy adults aged 50+ years were randomised to one of the following for 4 weeks: vitamin D fortified olive oil dairy drink, vitamin D fortified coconut oil dairy drink, vitamin D supplement or placebo control dairy drink. All vitamin D groups received 20µg of vitamin D3 daily. Serum was collected at baseline and post-intervention to measure 25(OH)D concentrations and biomarkers of metabolic health. Repeated measures general linear model analysis of covariance (RM GLM ANCOVA) compared changes over time. There was a significant time*treatment interaction effect on 25(OH)D concentrations for those classified as vitamin D insufficient (p < 0.001) and sufficient at baseline (p=0.004). 25(OH)D concentrations increased significantly for all insufficient participants receiving vitamin D3 in any form. However, for vitamin D sufficient participants at baseline, 25(OH)D concentrations only increased significantly with the coconut oil dairy drink and supplement. There was no effect of vitamin D on biomarkers of metabolic health. Vitamin D fortification of lipid-containing foods may be used in lieu of supplementation when supplement adherence is low or for individuals with dysphagia. These results are important given the recent recommendation to increase vitamin D intakes to 15-20µg for older adults in Ireland.