Bioavailability and efficacy of vitamin D₂ from UV-irradiated yeast in growing, vitamin D-deficient rats

New food sources are needed to bridge the gap between vitamin D intake and recommended intake. We assessed the bioavailability and efficacy of vitamin D in an 8 week dose-response study of bread made with vitamin D₂-rich yeast compared to vitamin D₃ in growing, vitamin D-deficient rats. Plasma 25-hydroxyvitamin D (25OHD) levels increased in a curvilinear, dose-dependent manner with both forms of vitamin D, but rats fed vitamin D ₂-rich yeast achieved lower levels than rats fed vitamin D ₃. Rats fed the highest doses of vitamin D had significantly greater (p < 0.05) trabecular BMC, BMD, bone volume, and connectivity density, and greater midshaft total cross-sectional area, compared to rats on the vitamin D-deficient diets, with no significant difference due to vitamin D source. Vitamin D₂-rich yeast baked into bread is bioavailable and improves bone quality in vitamin D-deficient animals.