A new study from New Zealand suggests that daily intakes of vitamin D3 are more effective than vitamin D2 in maintaining an adequate blood vitamin D concentration during the autumn and winter months.
To evaluate the effect of vitamin D2 or vitamin D3 intakes on 25-hydroxyvitamin D (25(OH)D) serum concentrations over the winter months in New Zealand (latitude 46°South), 95 healthy adults aged 18–50 years were randomly assigned to three groups which received either 25 micrograms (1000 IU) vitamin D3, 25 micrograms (1000 IU) vitamin D2 or placebo daily for 25 weeks (1). The mean total serum 25(OH)D concentrations (sum of 25(OH)D2 and 25(OH)D3) at the beginning of the study was 80 nanomoles per liter. After 25 weeks, total serum 25(OH)D concentrations were 21 nmol/l lower in participants who received vitamin D2 compared with those who took vitamin D3, among whom total serum 25(OH)D concentrations remained unchanged. Total serum 25(OH)D concentrations decreased substantially among the participants in the placebo group. Furthermore, there was a greater decrease in 25(OH)D3 levels observed in the D2-supplemented participants compared with placebo.
The researchers concluded that supplementation with vitamin D3 is more effective than vitamin D2, which confirms the results of earlier studies. The inability of vitamin D2 to maintain the total serum 25(OH)D levels could be partly explained by a more rapid metabolism or clearance of circulating 25(OH)D3 following D2 supplementation. The functional consequence of the differing metabolic response warrants further investi-gation.
Public health recommendations do not distinguish between vitamin D2 and vitamin D3, yet disagreement exists on whether these two forms should be considered equivalent. Vitamin D3 (cholecalciferol), the form produced in the skin of humans after exposure to sunlight, is found either naturally in animal products such as fatty fish and cod-liver oil, or added as a fortificant to foods or supplements. Vitamin D2 (ergocalciferol) is made either naturally or synthetically from the UV irradiation of ergosterol obtained from yeast, which is then added to foods. During recent years, a number of studies have been performed to investigate the relative potencies of two commonly used forms of vitamin D, finding that D3 is approximately 87% more potent in raising and maintaining serum 25(OH)D concentrations and produces two- to three-fold greater storage of vitamin D than does vitamin D2 (2,3).