Low bioaccessibility of vitamin D₂ from yeast-fortified bread compared to crystalline D₂ bread and D₃ from fluid...

The assessment of the efficacy of dietary and supplemental vitamin D tends to be confounded by differences in the serum 25-hydroxyvitamin D response between vitamin D₂ and vitamin D₃. Serum response differences from these vitamers may be due to differences in bioavailability. To address this specifically, the bioaccessibility was assessed for vitamin D₂ from breads fortified with UV-treated yeast, and a benchmark against staple vitamin D₃ fortified foods including bovine milks and infant formula, as well as crystalline vitamin D₂ fortified bread. Fortified foods were subjected to a three-stage static in vitro digestion model, and vitamin D was analyzed by HPLC-MS. Vitamin D bioaccessibility was significantly greater from bovine milks and infant formula (71-85%) than from yeast-fortified sandwich breads (6-7%). Bioaccessibility was not different between whole wheat and white wheat bread (p > 0.05), but was ∼4× lower from yeast-fortified bread than from crystalline vitamin D₂ fortified bread (p < 0.05). Intact yeast cells were observed in the digesta of yeast fortified bread. These results indicate that the low bioavailability of yeast D₂ in comparison to other vitamin D₂ sources is likely due to entrapment within a less digestible yeast matrix and not only to metabolic differences between vitamins D₂ and D₃.