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 D2-rich yeast achieved lower levels than rats fed vitamin D3. 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.