The D2-D3 Study: a randomised, double-blind, placebo-controlled food-fortification trial in women, comparing the efficacy of 15ug/d vitamin D2 vs vitamin D3 in raising serum 25OHD levels

Abstract

Poor vitamin D status (hypovitaminosis D) is a common problem in the UK; evidence shows prevalence is highest during the winter months, when serum 25OHD concentrations <25 and <40 nmol/l were found in 15•5% and 46•6% of the 1958 British birth cohort(1), compared to 3•2% and 15•4% respectively during the summer. As there are limited natural sources of vitamin D (diet and UVB rays) during the winter-time, supplementation and/or fortification of foods may be beneficial to proportions of the UK population. However, clarity on optimum type (vitamin D2 or D3) and dose of vitamin D required to maintain vitamin D status during the winter-time is urgently required(2). The D2-D3 study aimed to examine and compare the efficacy of vitamin D2 vs. vitamin D3 in raising serum 25OHD (s25OHD) levels, and to assess whether 15ug/d is sufficient to raise or maintain s25OHD levels above deficiency' or 'insufficiency' cut-offs (25 nmol/l and 40 nmol/l respectively) during the wintertime. In addition, the study aimed to compare the effect of two food vehicles on vitamin D bioavailability; orange juice and a biscuit. A total of 335 healthy women aged 20-64yrs were recruited and randomised to receive either placebo (PL), vitamin D2 in orange juice (D2J), vitamin D2 in a biscuit (D2B), vitamin D3 in orange juice (D3J), or vitamin D3 in a biscuit (D3B) daily for 12-weeks during the wintertime. At baseline, there were no significant differences in s25OHD levels between the five intervention groups. As shown in Table 1, after the 12-week intervention, all four vitamin D treatment groups showed a significant increase in s25OHD, whereas the placebo group had a significant decrease in s25OHD, as would be expected during the winter months. Food vehicle had no effect on the bioavailability of either vitamin D2 or vitamin D3. [TABLE PRESENTED] When comparing between the D2 and D3 intervention groups, irrespective of the food vehicle, the D3 group demonstrated a significantly greater increase in s25OHD over the 12-week intervention period (p< 0•0001). The present study provides conclusive evidence that food vehicle does not effect the bioavailability of vitamin D2 or vitamin D3, and that whilst both 15ug/d of vitamin D2 or D3 for 12-weeks are able to raise s25OHD levels during the wintertime, vitamin D3 is significantly more effective, facilitating a greater increase in s25OHD levels.