Effects of vitamin D2-fortified bread v. supplementation with vitamin D2 or D3 on serum 25-hydroxyvitamin D metabolites: an 8-week randomised-controlled trial in young adult Finnish women.

There is a need for food-based solutions for preventing vitamin D deficiency. Vitamin D-3 (D-3) is mainly used in fortified food products, although the production of vitamin D-2 (D-2) is more cost-effective, and thus may hold opportunities. We investigated the bioavailability of D-2 from UV-irradiated yeast present in bread in an 8-week randomised-controlled trial in healthy 20-37-year-old women (n 33) in Helsinki (60 degrees N) during winter (February-April) 2014. Four study groups were given different study products (placebo pill and regular bread=0 mu g D-2 or D-3/d; D-2 supplement and regular bread=25 mu g D-2/d; D-3 supplement and regular bread=25 mu g D-3/d; and placebo pill and D-2-biofortified bread=25 mu g D-2/d). Serum 25-hydroxyvitamin D-2 (S-25(OH)D-2) and serum 25-hydroxyvitamin D-3 (S-25(OH)D-3) concentrations were measured at baseline, midpoint and end point. The mean baseline total serum 25-hydroxyvitamin D (S-25(OH)D=S-25(OH)D-2+S-25(OH)D-3) concentration was 651 nmol/l. In repeated-measures ANCOVA (adjusted for baseline S-25(OH)D as total/D-2/D-3), D-2-bread did not affect total S-25(OH)D (P=0707) or S-25(OH)D-3 (P=0490), but increased S-25(OH)D-2 compared with placebo (P<0001). However, the D-2 supplement was more effective than bread in increasing S-25(OH)D-2 (P<0001). Both D-2 and D-3 supplementation increased total S-25(OH)D compared with placebo (P=0030 and P=0001, respectively), but D-2 supplementation resulted in lower S-25(OH)D-3 (P<0001). Thus, D-2 from UV-irradiated yeast in bread was not bioavailable in humans. Our results support the evidence that D-2 is less potent in increasing total S-25(OH)D concentrations than D-3, also indicating a decrease in the percentage contribution of S-25(OH)D-3 to the total vitamin D pool.