Vitamin D and cancer mini-symposium: the risk of additional vitamin D.
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.
Department of Nutritional Sciences, University of Toronto, and Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada. rvieth@mtsinai.on.ca
Reinhold
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Vieth
D000328:Adult; D003226:Congresses as Topic; D000075202:Contraindications; D006801:Humans; D006934:Hypercalcemia / Q000139:chemically induced*; D009369:Neoplasms / Q000209:etiology*; D018570:Risk Assessment; D014807:Vitamin D / Q000008:administration & dosage / Q000009:adverse effects* / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology; D014809:Vitamin D-Binding Protein / Q000378:metabolism; D014815:Vitamins / Q000008:administration & dosage / Q000494:pharmacology
D014809:Vitamin D-Binding Protein; D014815:Vitamins; D014807:Vitamin D; C104450:25-hydroxyvitamin D