The vitamin D precursor in our skin is converted to 25-hydroxyvitamin D, which is then further converted to 1,25-dihydroxyvitamin D, the most active form of vitamin D in our body. Despite this, many of us are deficient in vitamin D and therefore rely on vitamin D supplements to get the vitamin D we need. When we consume vitamin D from foods and supplements, the vitamin D undergoes the same conversion process in our body to the most active form. Because supplements of vitamin D are found in two main forms, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), there is debate on which supplement form is best. Two new studies published within a couple of weeks of each other in the Journal of Endocrinology and Metabolism, tried to answer this question. In the first vitamin D study, researchers administered 50,000 IU of vitamin D2 or vitamin D3 to 33 healthy adults for 12 weeks and measured blood and tissue levels of 25-hydroxyvitamin D[1]. The investigators reported that vitamin D3 stimulated greater steady state blood levels of 25-hydroxyvitamin D (45 ng/ml) than did vitamin D2 (24 ng/ml). Vitamin D2 supplementation only increased body fat content of vitamin D2 by 50 mcg/kg, while vitamin D3 supplementation increased body fat content of vitamin D3 by 104 mcg/kg. Total body fat content of vitamin D rose substantially more after vitamin D3 supplementation compared to vitamin D2 supplementation. Overall, the study investigators indicated that intake of vitamin D3 was about 87% more effective at elevating and maintaining blood vitamin D levels and was 2 - 3 times more effective at inducing vitamin D storage compared to vitamin D2. In the second vitamin D study, older (over 65 years), community-dwelling adults were given either vitamin D2 or vitamin D3 in doses of 1,600 IU daily for one year or 50,000 IU monthly for one year[2]. Blood levels of 25-hydroxyvitamin D, calcium, and more were measured at various intervals during the 1-year treatment period. Administration of vitamin D2 caused an increase in 25-hydroxyvitamin D2, but also caused a decrease in 25-hydroxyvitamin D3. Overall, vitamin D3 supplementation was shown to be more effective at increasing blood levels of 25-hydroxyvitamin D. Interestingly, despite vitamin D supplementation, 19% of the study volunteers remained vitamin D deficient after 1 year. These two independent studies clearly indicate that vitamin D3 is the vitamin D supplement of choice if you are choosing to supplement your diet with vitamin D. While both vitamin D2 and vitamin D3 can be helpful in supplementing your diet with vitamin D, these studies make it clear that D3 is more effective at getting your blood levels of vitamin D up to where they should be and D3 appears to promote greater vitamin D storage for future use. Since different dietary supplements on the market might use one or the other form of vitamin D, make sure to read the nutrition/supplement facts panel to see if they are using vitamin D2 or vitamin D3. When given the opportunity, selecting the supplement with vitamin D3 appears to be the wise choice at this time.
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Vitamin D is a fat-soluble vitamin that is produced in our own body in response to exposure to the sun's ultraviolet rays.
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