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."