Magnesium Supplements: Forms, Doses and How to Compare Them

Magnesium is sold in more forms than any other mineral, and the form is usually more consequential than the number on the front of the bottle. This hub explains what separates one magnesium supplement from another and which figures on the label are worth comparing.

The two things most labels obscure

The compound is not the mineral. A tablet described as “magnesium oxide 500 mg” contains 500 mg of magnesium oxide, of which only a portion is magnesium itself. Different compounds carry different proportions of elemental magnesium, so two bottles showing the same milligram figure can deliver quite different amounts. Where a label gives both figures, the elemental one is the comparable number.

The serving is not always one unit. Many magnesium products count two or three capsules as a single serving. Every figure on the supplement facts panel refers to that serving, so a product that looks twice as strong may simply expect you to take twice as much.

The forms you will meet

Glycinate (also sold as bisglycinate) and citrate are the two most common in supplements, with oxide widely used because it is inexpensive. Malate, threonate, chloride, taurate and aspartate all appear, and blends combine several. Our guide to magnesium forms covers what distinguishes them on the label; glycinate vs citrate takes the two you are most likely to be choosing between.

Dose and upper limits

Recommended intakes are set by national authorities and differ by age and sex; the NIH Office of Dietary Supplements publishes the US figures. There is also an established upper limit that applies specifically to magnesium from supplements and medicines rather than from food, which is an unusual and easily missed distinction. Both are covered in our magnesium dosage guide.

Interactions worth knowing about

Magnesium supplements interact with several common medications, including some antibiotics, bisphosphonates and diuretics, and the interaction is often about timing rather than avoidance. People with reduced kidney function need medical advice before supplementing, because impaired excretion is the main route to magnesium accumulating to harmful levels. See side effects and interactions, and speak to a pharmacist if you take regular medication.

Comparing products

Once you know which form you want, the remaining variables are elemental dose per serving, serving burden, servings per container and price. Our magnesium supplement comparison filters the catalogue by form, strength, format and brand so you can line up comparable products directly.

References

• NIH Office of Dietary Supplements — Magnesium (Health Professional Fact Sheet)
• NIH Office of Dietary Supplements — Magnesium (Consumer Fact Sheet)
• NHS — Vitamins and minerals: Others