Vitamin D3 seems more appropriate than D2 to sustain adequate levels of 25OHD: a pharmacokinetic approach.

BACKGROUND/OBJECTIVES: The superiority of cholecalciferol (D3) over ergocalciferol (D2) in sustaining serum 25-hydroxy vitamin D (25OHD) levels is controversial. To compare D2 with D3 we performed a single-blind, placebo-controlled randomized trial spanning 11 weeks. SUBJECTS/METHODS: Healthy volunteers (n=33, aged 33.4±6 years) were divided into three groups (n=11, each): D2, D3 and placebo. Treatment started with a loading dose (100,000 IU) followed by 4800 IU/day (d) between d7 and d20 and follow-up until d77. Serum samples were obtained at baseline and at days 3, 7, 14, 21, 35, 49, 63 and 77. RESULTS: Baseline 25OHD values in the D2 group were lower than those in the D3 and placebo groups (P<0.01). Placebo 25OHD levels never changed. As after the loading dose both D2 and D3 groups had reached similar 25OHD levels, we tested equivalence of the area under the concentration × time curve (AUC) between d7 and d77. The AUC was 28.6% higher for D3 compared with D2, and both were higher with respect to placebo. At d77, D2 25OHD levels were higher than those at baseline, but similar to placebo; both were lower than D3 (P<0.04). According to raw data, the elimination half-life of 25OHD was 84 and 111 days under D2 and D3 supplementation, respectively; after subtracting the placebo values, the corresponding figures were 33 and 82 days. CONCLUSIONS: D2 and D3 were equally effective in elevating 25OHD levels after a loading dose. In the long term, D3 seems more appropriate for sustaining 25OHD, which could be relevant for classic and non-classic effects of vitamin D.

Vitamin D biology: from the discovery to its significance in chronic kidney disease.

Vitamin D was discovered and had its chemical structure described in the early years of the last century. Although classified as a nutrient because it was found in small quantities in butter, it soon became clear that exposure of skin to sunlight, supplies most of the vitamin D necessary for good health in human beings. Vitamin D (D3 or cholecalciferol) synthesis in the skin is extremely rapid and remarkably robust despite the complexity of the mechanisms involved. However, a number of factors related to latitude location, season, and skin characteristics can interfere with the photoproduction of vitamin D. The 2 forms of vitamin D (D3 or D2-ergocalciferol) are biologically inactive and require activation in the liver and kidney. The product of the first hydroxylation of vitamin D in the liver, 25-hydroxyvitamin D (25(OH)D), is the marker of vitamin D status. Hypovitaminosis D (serum 25(OH)D, <30 ng/mL) is highly prevalent in the general population, and patients with chronic kidney disease seem to be at higher risk for the development of hypovitaminosis D. It is believed that, besides the traditional factors, protein losses, gastrointestinal malabsorption, and defective skin synthesis of vitamin D might contribute to the elevated number of patients with suboptimal level of vitamin D status.