Magnesium: the mineral that does not do what the label implies
Involved in hundreds of enzyme systems, which is a fact about biochemistry rather than a reason to take more of it.
Key takeaways
- Magnesium is a cofactor in several hundred enzyme systems, which describes its role and is not a benefit of supplementation.
- Dietary sources are ordinary and well characterised, including leafy vegetables, legumes, nuts, seeds and whole grains.
- The preparations sold differ substantially in absorption and tolerability, so trial results do not transfer between them.
- Deficiency is a clinical diagnosis with real consequences and is not the same thing as a low ordinary intake.
Magnesium is a cofactor in several hundred enzyme systems. That sentence is true, it is repeated on almost every package, and it carries none of the meaning it is asked to carry. It describes what the mineral does in a body that has enough. It says nothing about what happens in a body that is given more, which is the single most reliably misread idea in supplement marketing: a nutrient being necessary is not evidence that additional intake is useful.
Where it comes from in a diet is unglamorous and well characterised. Green leafy vegetables, legumes, nuts and seeds, whole grains, and in many countries drinking water contribute a measurable share. None of these are exotic, and none of them are marketed.
The claim that deficiency is widespread rests heavily on a measurement that cannot support it. Serum magnesium reflects only a small fraction of the body's stores, and it is held within a narrow range by the kidney and by exchange with bone. A normal serum value does not exclude depletion, and a population survey of ordinary intakes below a reference value is not a survey of clinical deficiency. Deficiency is a clinical diagnosis with real consequences, and it is not the same thing as eating less than a recommended figure.
The populations in whom depletion is genuinely well documented are specific. People with certain gastrointestinal conditions involving malabsorption, people with particular kidney disorders, people with chronic alcohol use, and people taking some long term medicines including proton pump inhibitors and certain diuretics. The interactions run the other way too: magnesium containing preparations can reduce the absorption of some antibiotics and of bisphosphonates, which is why separation of administration is a clinical instruction rather than a detail.
The preparations sold differ substantially in solubility, absorption and gastrointestinal tolerability, so trial results obtained with one salt do not transfer to another. A nutrient with a real and thoroughly ordinary role attracts claims far beyond it, largely because the biochemistry sounds impressive and the food it comes from does not.
A shorter version of this piece first appeared as a LinkedIn post in July 2026.
Notes and sources
Each regulatory statement in this article is set against the document it comes from, so you can read the original rather than our summary of it.
1. Serum magnesium is a poor indicator of total body magnesium stores
NIH Office of Dietary Supplements, Magnesium fact sheet for health professionals
2. Long term proton pump inhibitor use has been associated with hypomagnesaemia
3. Dietary reference values for magnesium are population reference intakes, not diagnostic thresholds
