Magnesium
Not needed on a normal diet; fix a shortfall with food rather than a supplement
What it is
A mineral involved in more than 300 enzyme systems: protein synthesis, muscle and nerve function, blood glucose control and blood pressure regulation. Good sources are green leafy vegetables, legumes, nuts, seeds and whole grains.
Benefits
For trained people with an adequate intake, supplements do not improve performance (AIS, ISSN). In older people and pregnant women, groups at greater risk of deficiency, benefits for sleep, mood and cramps have been reported, but it is unclear whether they apply when intake is adequate (AIS). AIS calls the research too poor for recommendations.
Dose
Intake values cover magnesium from all sources, including food. US (NIH): 400–420 mg a day for men and 310–320 mg for women. Europe (EFSA): 350 mg for men and 300 mg for women. The sources give no recommended supplement dose for people who train; studies that found no effect used 500 mg a day.
When to take it
The sources give no advice on timing. But magnesium interacts with some medicines: take oral bisphosphonates at least 2 hours before or after it, and tetracycline or quinolone antibiotics at least 2 hours before or 4–6 hours after (NIH).
Who it's for
People at higher risk of a shortfall: those with gastrointestinal diseases, type 2 diabetes or alcohol dependence, and older adults (NIH). Intake can also fall short on restrictive diets, but even then AIS prefers fixing the diet.
Who can skip it
Healthy people on a normal diet. Symptomatic deficiency from low intake is uncommon in healthy people because the kidneys limit magnesium losses (NIH), and extra magnesium is unlikely to help when intake is adequate (AIS).
Forms
Supplements contain magnesium oxide, citrate, chloride and other salts. NIH ODS: forms that dissolve well in liquid are absorbed more completely; aspartate, citrate, lactate and chloride tend to be absorbed better than oxide and sulfate. A 2019 study (in its introduction, citing earlier work): organic salts (such as citrate) are more bioavailable than inorganic ones (oxide) but provide less elemental magnesium. The sources read contain no human comparisons of glycinate with other forms.
Safety
The upper level excludes magnesium from food: 350 mg a day from supplements and medicines (NIH); 250 mg from supplements, water and fortified foods (Europe's SCF). High supplement doses often cause diarrhoea, sometimes with nausea and cramps. Very large doses are toxic: low blood pressure, muscle weakness, irregular heartbeat; the risk is higher with impaired kidney function. Diuretics and proton pump inhibitors affect magnesium levels (NIH).
From regular food
This is a summary of public sources, not medical advice. If you have a health condition, are pregnant or take medication, talk to a doctor before taking a supplement.
Sources
- Magnesium — Fact Sheet for Health Professionals . NIH Office of Dietary Supplements, 2026.
- AIS Sports Supplement Framework — Group C . Australian Institute of Sport, 2026.
- Scientific Opinion on Dietary Reference Values for magnesium . European Food Safety Authority, 2015.
- Tolerable Upper Intake Levels for Vitamins and Minerals (Scientific Committee on Food opinion on magnesium) . European Food Safety Authority / Scientific Committee on Food, 2006.
- ISSN exercise & sports nutrition review update: research & recommendations . International Society of Sports Nutrition, 2018.
- Predicting and Testing Bioavailability of Magnesium Supplements . Nutrients, 2019.
Other supplements
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