Marina Shkayeva, PharmD: No relevant financial relationship(s) with ineligible companies to disclose.
Objectives: To characterize magnesium-containing dietary supplements on the market by magnesium amount per serving and salt form.
Methods: The Dietary Supplement Label Database (DSLD) from the National Institutes of Health was chosen as the data source to characterize how many supplements contain an amount of magnesium that is at the tolerable upper intake level (UL) or above. DSLD was searched for all dietary supplement labels that contain magnesium. Label data were downloaded into an Excel spreadsheet and characterized based on target age group, amount of magnesium contained per serving, and magnesium salt form.
Results: A total of 18722 magnesium-containing dietary supplement label entries were reviewed. Excluded from further characterization were 4658 labels containing magnesium only as an additive or a tablet binder. A total of 14064 labels listed magnesium as a dietary supplement ingredient. Of these, 13821 labels were for people 4 years and older, 236 were for pregnant or lactating women, and 7 were for toddlers aged 1–4. From the dietary supplements targeting people 4 years and older, 1295 (about 9.4%) contained more than 350 mg of magnesium per serving, and 58 contained 350 mg magnesium per serving, which is the UL for adults and children 9 years and older. A total of 19 (about 8%) magnesium-containing supplements for pregnant and lactating women contained more than 350 mg magnesium per serving. None of the 7 supplements for children under 4 years of age contained more than the UL. Finally, 1106 supplement labels did not list the amount of magnesium per serving and could not be characterized.
The salt forms of magnesium in dietary supplements varied and were not always listed on the label. From a sample of 58 supplement labels containing the UL of magnesium per serving, most contained the salts magnesium carbonate and magnesium oxide (43% and 27%, respectively). These magnesium salts are relatively poorly absorbed (4-30%).
Conclusions: Some magnesium-containing dietary supplements on the market exceed the tolerable upper intake level as set by the Institute of Medicine and have an increased risk of causing dose-related adverse effects. Forms of magnesium commonly appearing in dietary supplements are not always chosen to optimize magnesium absorption.
