1 Holick MF "Vitamin D deficiency". N.Engl. J. Med. (2007) 357 (3): 266-81.

2 Dietary Supplemental Fact Sheet: Vitamin D. Office of Dietary Supplements. National Institutes of Health. Updated 11/13/2009. Accessed 08/17/2010

3 CDC website (http://www.cdc.gov/labstandards/hs_procedures.html)

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