The bioavailability of vitamin D3, a model hydrophobic nutraceutical, in casein micelles, as model protein nanoparticles: Human clinical trial results

The use of protective protein-based nanovehicles to deliver hydrophobic nutraceuticals raises important questions regarding their consequent bioavailability compared to that inside fat, or in its presence. To answer that, vitamin-D3 was chosen as a model lipophilic-bioactive, re-assembled casein micelles (rCM) as a protein-based nanovehicle and 0% fat yoghurt as a model nonfat food. We performed a single-high-dose-ingestion clinical trial with 94 healthy human volunteers, each receiving 150 g yoghurt containing 50,000 IU of vitamin-D3. Vitamin-D3 was either in rCM in the absence or presence of fat, or dissolved in milk fat. Un-enriched nonfat yoghurt was the negative control. The bioavailability of vitamin-D3 was determined by measuring its status-indicator: serum 25-hydroxyvitamin D level. The bioavailability of vitamin-D3 within the protein nanoparticles in the absence of fat was found to be insignificantly different from its bioavailability within fat, suggesting that the bioavailability of lipophilic bioactives in protein nanovehicles is not lower than in fat.