Abstract 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°N) during winter (February–April) 2014. Four study groups were given different study products (placebo pill and regular bread=0 µg D 2 or D 3 /d; D 2 supplement and regular bread=25 µg D 2 /d; D 3 supplement and regular bread=25 µg D 3 /d; and placebo pill and D 2 -biofortified bread=25 µg 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 65·1 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 =0·707) or S-25(OH)D 3 ( P =0·490), but increased S-25(OH)D 2 compared with placebo ( P <0·001). However, the D 2 supplement was more effective than bread in increasing S-25(OH)D 2 ( P <0·001). Both D 2 and D 3 supplementation increased total S-25(OH)D compared with placebo ( P =0·030 and P =0·001, respectively), but D 2 supplementation resulted in lower S-25(OH)D 3 ( P <0·001). 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.
Abstract Increased vitamin D fortification of dairy products has increased the supply of vitamin D-containing products with different vitamin D contents on the market in Finland. The authors developed a ninety-eight-item FFQ with eight food groups and with a question on supplementation to assess dietary and supplemental vitamin D and Ca intakes in Finnish women (60ºN). The FFQ was validated in subgroups with different habitual vitamin D supplement use (0–57·5 µg/d) against the biomarker serum 25-hydroxyvitamin D (S-25(OH)D) and against 3-d food records (FR) ( n 29–67). Median total vitamin D intake among participants was 9·4 (range 1·6–30·5) µg/d. Spearman’s correlations for vitamin D and Ca ranged from 0·28 ( P 0·146, FFQ v . S-25(OH)D, persons not using supplements) to 0·75 ( P <0·001, FFQ v . FR, supplement use included). The correlations between the FFQ and S-25(OH)D concentrations improved within increasing supplement intake. The Bland–Altman analysis showed wide limits of agreement between FFQ and FR: for vitamin D between −7·8 and 8·8 µg/d and for Ca between −938 and 934 mg/d, with mean differences being 0·5 µg/d and 2 mg/d, respectively. The triads method was used to calculate the validity coefficients of the FFQ for vitamin D, resulting in a mean of 1·00 (95 % CI 0·59, 1·00) and a range from 0·33 to 1·00. The perceived variation in the estimates could have been avoided with a longer FR period and larger number of participants. The results are comparable with earlier studies, and the FFQ provides a reasonable estimation of vitamin D and Ca intakes.
