The Pharmacology of Vitamin D

Vitamin D (Third Edition) 2011, Pages 1041-1066
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doi:10.1016/B978-0-12-381978-9.10057-5
Reinhold Vieth : University of Toronto, Toronto, Canada and Mount Sinai Hospital, Toronto, Canada

Vitamin D dosage depends on the target concentration of 25-hydroxyvitamin D (25(OH)D) desired. A useful rule of thumb is that an incremental dose of 1 ?g/day (40 IU) of vitamin D3 raises 25(OH)D by 1 nmol/L after 8 months of use. (Equivalent to 100 IU/day increases 25(OH)D by 1 ng/mL.) If the same cumulative dose of vitamin D is given, there is no difference in efficacy between daily, weekly, or monthly dose intervals. Hypercalcemia is the classic criterion for toxicity of vitamin D, its metabolites and their analogs. “Non-calcemic” doses are considered “safe” by conventional criteria. Levels of 25(OH)D >75 nmol/L (>30 ng/mL) generally relate to lower risk of colorectal cancer, bone fractures, and desirable health outcomes. To ensure levels higher than this in adults requires vitamin D3 at an average total input from sunshine, diet and/or supplements of 75 ?g/day (3000 IU/day).

• Overview of the System of Vitamin D Metabolism and its Regulation
• • Hypothesis that Large Fluctuations in 25(OH)D Concentrations are Adverse
• • Role of Vitamin D Binding Protein (DBP)
• Placebo-Controlled Clinical-Trial Justification for an Optimal Serum 25(Oh)D Level
• • Non-bone Effects of Vitamin D
• Dosage Considerations
• • Infants
• • Adults
• • The Case against Ergocalciferol, Vitamin D2
• • UVB Light Skin as a Dose of Vitamin D
• Pharmacokinetic Principles, Volume of Distribution, Turnover and Half-Life as it Pertains to Vitamin D
•• Body Storage of Vitamin D and Inefficient Conversion to 25(OH)D
• Vitamin D Toxicity and Safety Issues
• The Concept of a Loading Dose
• • The Problem with Weekly 50 000 IU Vitamin D2 as a Loading Dose
• • At What Point is a Loading Dose Toxic?
• Summary and Conclusions