TORONTO, CANADA. The current RDA (Recommended Dietary Allowance) for vitamin-D is 400 IU/day (10 micrograms/day). Researchers at the University of Toronto now provide convincing evidence that this RDA is far too low. They point out that a blood serum level of less than 40-50 nmol/L of 25(OH)D (the active metabolite of vitamin-D) indicates deficiency and that a level of 75 to 100 nmol/L is required for optimum health.
The researchers carried out a clinical experiment involving 61 healthy men and women. The participants were assigned to receive either 1000 IU (25 micrograms) or 4000 IU (100 micrograms) of vitamin-D3 for a three-month period starting between January and February. At baseline (before supplementation) 62 per cent of these presumably healthy Canadians were found to be vitamin-D deficient [25(OH)D concentration below 40 nmol/L] and 16 per cent were severely so [25(OH)D below 25 nmol/L].
The supplementation increased the average 25(OH)D level to 69 nmol/L in the 25 micrograms/day group and to 96 nmol/L in the 100 micrograms/day group. The 25- microgram dosage was sufficient to increase the 25(OH)D level to the desirable 75 nmol/L or higher in 35 per cent of the subjects. The 100-microgram dosage achieved this aim in 88 per cent of the subjects. There were no significant increases in serum calcium level and no adverse effects. The researchers conclude that 100 micrograms/day (4000 IU/day) of vitamin-D3 is a safe and desirable intake. They very specifically caution that their findings regarding vitamin-D3 (cholecalciferol) cannot be applied to the synthetic version of vitamin-D2 (ergocalciferol), the form most often used in North America. Vitamin-D2 is far more toxic than vitamin-D3 and produces unique metabolites not generated by vitamin-D3. The researchers are very "down" on vitamin-D2 and say, "It is an anachronism to regard vitamin-D2 as a vitamin."
Vieth, Reinhold, et al. Efficacy and safety of vitamin D intake exceeding the lowest observed adverse effect level. American Journal of Clinical Nutrition, Vol. 73, February 2001, pp. 288-94 [47 references]