Ann Epidemiol. 2009 Jul;19(7):441-5. Epub 2009 Apr 11.
Vitamin D and cancer mini-symposium: the risk of additional vitamin D.
Vieth R. Department of Nutritional Sciences, University of Toronto, and Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada. rvieth at mtsinai.on.ca
Any benefit of vitamin D needs to be balanced against the risk of toxicity, which is characterized by hypercalcemia. Daily brief, suberythemal exposure of a substantial area of the skin to ultraviolet light, climate allowing, provides adults with a safe, physiologic amount of vitamin D, equivalent to an oral intake of about 10,000 IU vitamin D(3) per day, with the plasma 25-hydroxyvitamin D (25(OH)D) concentration potentially reaching 220 nmol/L (88 ng/mL).
The incremental consumption of 40 IU/d of vitamin D(3) raises plasma 25(OH)D by about 1 nmol/L (0.4 ng/mL). High doses of vitamin D may cause hypercalcemia once the 25(OH)D concentration is well above the top of the physiologic range. The physiological buffer for vitamin D safety is the capacity of plasma vitamin D-binding protein to bind the total of circulating 25(OH)D, vitamin D, and 1,25-dihydroxyvitamin D 1,25(OH)2D.
Hypercalcemia occurs when the free concentration is inappropriately high because vitamin D and its other metabolites have displaced 1,25(OH)2D from vitamin D-binding protein.
Evidence from clinical trials shows, with a wide margin of confidence, that a prolonged intake of 10,000 IU/d of vitamin D(3) poses no risk of adverse effects for adults, even if this is added to a rather high physiologic background level of vitamin D. PMID: 19364661