Evaluation of vitamin D medicines and dietary supplements and the physicochemical analysis of selected formulations

Abstract

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.

Figure 1

Strengths of vitamin D3 formulations available in different countries. Total number of formulations per country; New Zealand = 31, Australia = 33, USA = 48, UK = 29, Japan = 79, Canada = 58, India = 40 and Malaysia = 15. Note, 40 IU = 1 µg

Figure 2

Average percentage of label claim for various formulations; TAB = tablet, SGC = soft gellatin capsule, HGC1 = hard gellatin capsule and EML = emulsion (error bars represents standard deviation, n=3). Dark grey bars represent formulations within 100 ± 10% of the label claim, black bars formulations above 110% and light grey bars formulations under 90%