Magnesium is having a moment as the sleep-and-relaxation mineral. Its actual evidence is narrower: supplementation nudges blood pressure down modestly in trials, and nothing much else holds up. If your diet is decent, you are unlikely to be deficient; if it is not, food fixes that faster than pills.
A 2025 meta-analysis of randomised controlled trials in Hypertension mapped magnesium supplementation to small systolic and diastolic blood-pressure reductions, examined across doses and durations. Effects on sleep quality, cramps and anxiety in replete adults remain poorly supported by controlled data. No trial links supplementation to fewer heart attacks or deaths in people without deficiency.
Doing it: Nuts, beans, whole grains and leafy greens deliver magnesium with the fibre and potassium that come packaged alongside it. If you supplement anyway, oxide forms are cheap but harsh on the stomach; citrate or glycinate are gentler. Loose stools mean you are taking more than you absorb.
Who it suits: Possibly worthwhile with documented low intake, chronic PPI or diuretic use, or persistent cramps your doctor has evaluated. Everyone else is mainly funding placebo with good marketing.
Sources
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