Magnesium-rich foods: how much you need and what the evidence says

Magnesium is a cofactor in more than 300 enzyme systems, including those for muscle and nerve function, blood glucose control and blood pressure regulation NIH ODS. The Recommended Dietary Allowances set by the National Academies are:

About 30% to 40% of the magnesium in food is absorbed NIH ODS. Because most of the body's magnesium sits inside cells and bone, a blood test does not show your total stores well, which is one reason "do I need magnesium?" is hard to answer from a lab result alone.

Those figures come from the NIH Office of Dietary Supplements table NIH ODS. A day built on whole foods gets there without much effort: a handful of almonds, half a cup of black beans, a serving of brown rice and a cup of soymilk already add up to over 240 mg. The nuts and beans and lentils pages cover those foods in more depth.

Many people in the US eat less magnesium than recommended, and men over 70 and teenagers are the most likely to have low intakes NIH ODS. Clear deficiency is uncommon in healthy people, because the kidneys hold on to magnesium when intake is low. The groups at higher risk are people with gastrointestinal diseases such as Crohn's or celiac disease, people with type 2 diabetes, people with long-term alcohol dependence, and older adults NIH ODS; NIH ODS.

Early signs of deficiency are vague: loss of appetite, nausea, vomiting, fatigue and weakness. Numbness, cramps, seizures and abnormal heart rhythms come later and need medical care NIH ODS. If you want to see what your usual meals provide before thinking about a supplement, a food diary app such as Cronometer reports magnesium from its food database.

Almost all the trials below used supplements rather than food, so they tell you what extra magnesium does, not what a seed-and-bean diet does.

• Blood pressure. Across 34 double-blind trials, a median 368 mg a day lowered blood pressure by about 2 mm Hg systolic and 1.8 mm Hg diastolic Zhang 2016. NIH ODS describes the effect as marginal NIH ODS.
• Sleep. Three small trials in 151 older adults with insomnia found they fell asleep about 17 minutes sooner, with no significant change in total sleep time, and the evidence was rated low to very low quality Mah 2021. The sleep page covers the bigger levers.
• Migraine. In several small trials, people with migraine who took magnesium supplements had modestly fewer migraines NIH ODS. A 2012 American Academy of Neurology and American Headache Society guideline rated magnesium "probably effective" (Level B) for reducing how often migraines occur Holland 2012. NIH ODS advises taking magnesium for this only under the care of a health care provider NIH ODS.
• Blood sugar. Eighteen trials found supplements lowered fasting glucose in people with diabetes and improved glucose tolerance in people at high risk Veronese 2016, but the American Diabetes Association says the evidence is not enough to recommend magnesium for glycemic controlNIH ODS.

Food comes first: magnesium from food and drink is not harmful and does not need to be limited, because healthy kidneys clear the excess NIH ODS. Supplements and medicines are different. The upper limit for magnesium from supplements and medications is 350 mg a day for adults; above that, diarrhea, nausea and cramping are common, and very high doses can cause dangerous toxicityNIH ODS. The risk is higher with reduced kidney function NIH ODS. Citrate, aspartate, lactate and chloride forms tend to be absorbed better than oxideNIH ODS.