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Department of Nutritional Sciences and Department of Laboratory Medicine and Pathology, University of Toronto, and Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada M5G 1L5
2 To whom correspondence should be addressed. E-mail: rvieth{at}mtsinai.on.ca.
The tolerable upper intake level (UL) for vitamin D is 50 mcg/d (2000 IU/d) in North America and in Europe. In the United Kingdom a guidance level exists for vitamin D, 25 mcg/d (1000 IU/d), defined as the dose "of vitamins and minerals that potentially susceptible individuals could take daily on a life-long basis, without medical supervision in reasonable safety." Exposure of skin to sunshine can safely provide an adult with vitamin D in an amount equivalent to an oral dose of 250 mcg/d. The incremental consumption of 1 mcg/d of vitamin D3 raises serum 25-hydroxyvitamin D [ 25(OH)D ] by 
1 nmol/L (0.4 µg/L). Published reports suggest toxicity may occur with 25(OH)D concentrations beyond 500 nmol/L (200 µg/L). Older adults are advised to maintain serum 25(OH)D concentrations >75 nmol/L. The preceding numbers indicate that vitamin D3 intake at the UL raises 25(OH)D by 50 nmol/L and that this may be more desirable than harmful. The past decade has produced separate North American, European, and U.K. reports that address UL or guidance-level values for vitamin D. Despite similar well-defined models for risk assessment, each report has failed to adapt its message to new evidence of no adverse effects at higher doses. Inappropriately low UL values, or guidance values, for vitamin D have hindered objective clinical research on vitamin D nutrition, they have hindered our understanding of its role in disease prevention, and restricted the amount of vitamin D in multivitamins and foods to doses too low to benefit public health.
KEY WORDS: • vitamin D • cholecalciferol • hypercalcemia • tolerable upper intake level • 25-hydroxyvitamin D • toxicology
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