Magnesium benefits: what the trials actually show

How strong is the evidence for each claim?

We grade each claim on human trials only, using the four grades explained here. The grade describes how sure we can be, not how big the effect is: some well-proven effects are small.

Why do so many claims rest on so little?

Because magnesium is involved in hundreds of chemical reactions in the body, including energy production, nerve signalling, muscle contraction and the control of blood sugar. That makes it easy to tell a convincing story about almost any symptom. Observational studies add to the impression: people with migraine, diabetes, depression and high blood pressure tend to have lower magnesium levels.

But a link is not proof. Illness, poor diet, alcohol and several common medicines all lower magnesium, so low levels may be a consequence rather than a cause. The question that matters is whether taking magnesium makes people better, and that needs placebo-controlled trials.

Who is most likely to benefit?

Across the trials, the clearest benefits appeared in people who were likely to be short of magnesium to start with: older adults, people with type 2 diabetes or insulin resistance, and people with low dietary intakes. If you eat well, the benefit may be small or nil.

People who regularly take medicines that drain magnesium, such as long-term acid-reducing tablets or some diuretics, can become genuinely deficient. That needs a blood test and advice from a GP, not guesswork.

What about forms and doses?

Most trials used 250 to 600 mg of elemental magnesium a day, often as magnesium oxide or citrate. There is little head-to-head evidence that one form works better than another for any of these conditions. See forms of magnesium for how they differ and dosage and timing for how much to take.