Why the optimal requirement for Vitamin D3 is probably much higher than what is officially recommended for adults
The Journal of Steroid Biochemistry and Molecular Biology, Volumes 89–90, May 2004, Pages 575–579
Proceedings of the 12th Workshop on Vitamin D
Reinhold ViethCorresponding author contact information, E-mail the corresponding author
Department of Laboratory Medicine and Pathobiology, University of Toronto, and Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada M5G 1X5
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. 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. 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. One mcg per day of Vitamin D3 (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 15 mcg per day do not meet the criterion of an RDA.
Fig. 2. Dose–response curve, summarizing randomized-control clinical trials of fracture-prevention using Vitamin D, with or without calcium. None of the studies using doses of Vitamin D3 providing less than 20 mcg per day was effective in reducing fracture risk and . However, all the studies in which there was a reduction in fracture risk used approximately 20 mcg per day of Vitamin D3, , and . This dose includes the known background intake; for the work by Dawson-Hughes background intake, this was 5 mcg per day [44]. The question mark is included in the figure to emphasize that there have been no studies looking at effects of Vitamin D3 beyond 20 mcg per day.