Vitamin D Supplementation: An Update

Christine Gonzalez, PharmD, CHHC

US Pharmacist

Deficiency, Blood Concentrations, and Toxicity

Risk factors for vitamin D deficiency include living in northern latitudes (in the U.S., above the line from San Francisco to Philadelphia), failing to get at least 15 minutes of direct sun exposure daily, being African American or dark-skinned, being elderly, or being overweight or obese.^[5] Rickets and osteomalacia are the well-known diseases of severe vitamin D deficiency. Musculoskeletal pain and periodontal disease may also indicate a significant vitamin D deficiency.^[7] Subtle symptoms of milder deficiency include loss of appetite, diarrhea, insomnia, vision problems, and a burning sensation in the mouth and throat.^[7] Drawing a blood calcidiol concentration is the standard test for vitamin D status, since calcidiol has a longer half-life.^[8]

A normal range of vitamin D is 30 to 74 ng/mL, but this can vary among laboratories.^[8] Most experts agree that a concentration between 35 and 40 ng/mL is reasonable for preventive health. Some suggest that the optimal concentration for protecting against cancer and heart disease is between 50 and 70 ng/mL and up to 100 ng/mL. Side effects or toxicity can occur when blood concentrations reach 88 ng/mL or greater.^[9] Symptoms include nausea, vomiting, constipation, headache, sleepiness, and weakness.^[6] Too much vitamin D can raise blood calcium concentrations, and acute toxicity causes hypercalcemia and hypercalciuria.^[6,9]

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Cite this: Vitamin D Supplementation: An Update - Medscape - Oct 01, 2010.

Abstract and Introduction
Pharmacology
Deficiency, Blood Concentrations, and Toxicity
Disease Prevention
Dosing
Drug Interactions
Future Research
Conclusion
References

Table 1. Forms of Vitamin D
Cholecalciferol (vitamin D₃) Naturally occurring form of vitamin D; made by the skin upon sun exposure; found in foods and most supplements
Calcidiol (25-hydroxyvitamin D₃) Prehormone made directly from cholecalciferol in the liver; low biologic activity, but major form circulating in the bloodstream; concentrations measured by typical blood test for vitamin D deficiency
Calcitriol (1,25-dihydroxyvitamin D₃) Activated form made from calcidiol in the kidneys and tissues; the most potent steroid hormone in the body
Ergocalciferol (vitamin D₂) Made in the laboratory by radiating fungus; not naturally occurring in the body; used in prescription vitamin D (Drisdol), available in 50,000-IU capsules

Table 2. Dosing and Blood Concentrations
Dosage	Expected Increase in Blood Concentration
100 IU	1 ng/mL
200 IU	2 ng/mL
400 IU	4 ng/mL
800 IU	8 ng/mL
1,000 IU	10 ng/mL
2,000 IU	20 ng/mL

Source: Reference 30.

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