University of Toronto researchers argue that the optimal vitamin D-3 requirement probably is much higher than the current recommended daily allowance.
"The physiologic range for circulating 25-hydroxyvitamin D3 [25(OH)D; the measure of vitamin D nutrient status] concentration in humans and other primates extends to beyond 200 nmol/L (>80 ng/mL). This biologic 'normal' value is greater than current population norms for 25(OH)D. Concentrations of 25(OH)D that correlate with desirable effects extend to at least 70 nmol/L, with no obvious threshold," stated R. Vieth and colleagues.
"Randomized clinical trials using 20 mcg (800 IU) per day of vitamin D show that this suppresses parathyroid hormone, preserves bone mineral density, prevents fractures, lowers blood pressure, and improves balance," the study authors said.
"Calcium absorption from diet correlates with 25(OH)D in the normal range. Health effects of vitamin D beyond osteoporosis are mostly supported by the circumstantial evidence of epidemiologic studies and laboratory research. These include prevention of cancer and the autoimmune diseases, insulin-dependent diabetes, and multiple sclerosis," Vieth and colleagues wrote.
"One mcg per day of vitamin D-3 (cholecalciferol) increases circulating 25(OH)D by about 1 nmol/L (0.4 ng/mL). A recommended dietary allowance (RDA) is the long-term daily intake level that meets the total requirements for the nutrient by nearly all healthy individuals (it would presume no sunshine). If 70 nmol/L is regarded as a minimum desirable target 25(OH)D concentration, then current recommendations of 15mcg per day do not meet the criterion of an RDA," the researchers concluded.
Vieth and coauthors published the results of their research in the Journal of Steroid Biochemistry and Molecular Biology (“Why the optimal requirement for vitamin D-3 is probably much higher than what is officially recommended for adults.” J Steroid Biochem Mol Biol, 2004;89-90(1-5 Sp. Is):575-579).
For additional information, contact R. Vieth, University of Toronto, Dept. of Laboratory Med & Pathobiol, Toronto, ON M5G 1X5, Canada.