EVALUATION OF VITAMIN D MEDICINES AND DIETARY SUPPLEMENTS AND THE PHYSICOCHEMICAL ANALYSIS OF SELECTED FORMULATIONS

Context: Vitamin D is purported to offer wide ranging and numerous health benefits leading to increased interest from manufacturers of medicines and dietary supplements. Elderly patients frequently require vitamin D supplementation due to reduced sun exposure and dietary intake. There are ever increasing numbers of vitamin D formulations in the global market. However, due to a lack of regulatory restrictions for some of these products the quality of these dosage forms can be of some concern. Objectives: To study vitamin D formulations available in the global market and evaluate physic-chemical properties of selected formulations from the New Zealand market. Method: The first component of this study consisted of a search for different vitamin D formulations available in selected countries. The second component of the study involved assaying selected vitamin D formulations available in New Zealand. Vitamin D was extracted from capsule, tablet and emulsion formulations and quantified using a validated High Performance Liquid Chromatography (HPLC) method. Results: Of the 14 analysed formulations, only 60% were within 100 +/- 10 % of the label claim. The two registered, prescription formulations available exhibited vitamin D levels of 90 +/- 4% and 97 +/- 2% of the labeled amount, while non-registered, non-prescription dietary supplements had vitamin D levels ranging from 8 +/- 2% to 201 +/- 29% of the labeled amount. Conclusions: Dietary supplements do not require strict regulation and showed a large variation in the percentage label claim of vitamin D. Prescription formulations which are more strictly regulated gave content values within standard acceptance ranges. Vitamin D has proven health benefits and also the potential to cause harm, therefore there is a need for tougher regulations of dietary supplements to ensure acceptable quality.