Magnesium

Magnesium is an essential mineral. Your body uses it in more than 300 enzyme reactions, says the NIH (the US National Institutes of Health). These reactions make energy, build protein and DNA, and control nerves and muscles. An adult body holds about 25 g of magnesium, and 50% to 60% of it sits in bone.

Here is the part most people do not know: less than 1% of your body’s magnesium is in the blood. The body keeps that level under tight control, so a normal blood test does not show how much you have stored. The NIH says serum levels (the amount in the liquid part of blood) have little link with total body magnesium. NHANES, the US national health survey, has not measured serum magnesium since 1974.

Many people eat less than the targets. In US survey data from 2013 to 2016, 48% of Americans got less magnesium from food and drinks than their average requirement. Outright deficiency is uncommon in healthy people, because the kidneys limit how much is lost.

The EU target is not a measured requirement either. EFSA, the EU’s food safety agency, set it from what people in nine EU countries actually eat.

Health benefits of magnesium

• ★★★Fewer seizures in pregnancy with pre-eclampsiaA magnesium sulfate drip in hospital cut the risk of seizures to 0.41 times the risk without it, across 6 trials. In one large trial, seizures struck 0.8% of women on magnesium and 1.9% on placebo; this was not a pill.
• ★★★Unlikely to prevent cramps in older adultsMagnesium supplements gave 0.18 fewer night leg cramps a week than a dummy pill in older adults, a gap that could be chance. Gut side effects such as diarrhea hit 11% to 37% on magnesium.
• ★★Slightly lower blood pressure from supplementsAcross 34 trials, the top number fell about 2 points (2.00 mm Hg systolic) on magnesium supplements. A review of 12 trials in people with raised blood pressure found no clear drop in the top number.
• ★★Less constipation with magnesium oxideIn adults with long-term constipation, symptoms improved in 68.3% on magnesium oxide, against 11.7% on placebo, over 28 days. A smaller trial in women found 70.6% against 25.0%.
• ★★May help prevent migraine, results mixedA US guideline rates magnesium probably effective for migraine, but the dose exceeds the upper level for supplements, so use it only under medical direction. In one trial attacks fell 41.6% on 600 mg a day, against 15.8% on placebo; another found no benefit.

Foods high in magnesium

Seeds, beans, nuts and whole grains lead. Hemp seeds top our USDA ranking per serving: 3 tablespoons (30 g) hold 210 mg of magnesium. That is 50% of the 420 mg Daily Value (DV), the amount used on US food labels. Pumpkin seeds follow with 168 mg per ounce (28 g), then soybeans with 148 mg per cup and black beans.

Per 100 g, hemp seeds (700 mg) lead again, ahead of cocoa powder, flaxseeds and Brazil nuts. For the same calories (per 100 kcal), leafy greens and herbs lead, with spinach at the top (343 mg). The ranking below shows the full lists.

The NIH table adds roasted pumpkin seeds at 156 mg per ounce and almonds at 80 mg per ounce. Boiled spinach has 78 mg per half cup. Refining grains removes the germ and bran, and with them much of the magnesium. A ½ cup of cooked brown rice has 42 mg, and white rice has 10 mg.

Your body absorbs 30% to 40% of the magnesium in food (NIH). Phytic acid (a plant compound that binds minerals) and phosphate can lower that. Yet in one study, almonds were absorbed as well as soluble magnesium acetate.

Water adds magnesium too, from 1 mg per liter to over 120 mg per liter depending on the source. In a small study, about half of the magnesium in mineral water was absorbed.

How magnesium works

The biochemistry below is well established. It comes from reviews and studies of how the body works, not from trials of extra magnesium in people.

Four ideas cover most of it. Magnesium works with ATP in hundreds of reactions, and most of it is stored in bone and muscle. The gut absorbs only part of what you eat, and the kidneys decide how much stays. Then comes what has been seen in people.

It works with ATP in more than 300 reactions

Magnesium is a helper (cofactor) for more than 300 enzyme reactions, according to EFSA. Many involve ATP, the molecule cells use to carry energy. Magnesium binds to ATP and helps the enzyme pass on its phosphate. That makes magnesium part of how cells make carbohydrates, fats, DNA, RNA and proteins.

The NIH adds that magnesium helps move calcium and potassium across cell membranes. That matters for nerve signals, muscle contraction and a normal heart rhythm. EFSA says magnesium is also part of the crystal structure of bone.

Most of it is stored in bone and muscle

EFSA puts the total at 20 to 28 g in a healthy adult, with about 60% in bone and about 25% in muscle. Some bone magnesium is tightly bound to the mineral. Some sits loosely on the crystal surface, where the body can release it when the diet falls short.

Only about 0.3% is in serum. That is why blood levels are a poor guide to your stores. EFSA says no suitable marker (biomarker) of magnesium status exists for setting intake values.

The gut absorbs only part of it

The NIH says about 30% to 40% of the magnesium in food and drink is absorbed. EFSA says 40% to 50% is typical, with figures from 10% to 70% reported. Absorption happens mainly in the small intestine, and phytic acid and phosphate can reduce it.

The share absorbed falls as the dose rises. In one study in healthy people, 65% was absorbed at the lowest intake and 11% at the highest. So your body does not absorb a large single dose in proportion.

The kidneys decide how much stays

Your kidneys pass about 120 mg of magnesium a day into urine, according to the NIH. They let less go when your stores are low. EFSA says only about 3% of the filtered magnesium ends up in urine. Most is taken back in a part of the kidney called the loop of Henle (60% to 70%), and more later along the tubule.

This control is why clear deficiency is uncommon in healthy people. It is also why damaged kidneys raise the risk of too much. Some drugs that act on the kidney increase magnesium loss, such as loop and thiazide diuretics (water pills).

What has been seen in people

The clearest human findings are about intake and loss. Surveys suggest many people eat less than the targets, and blood tests cannot tell who is low.

Trials of extra magnesium, all among the study cards above, show small effects. Blood pressure falls about 2 to 3 mm Hg, with larger drops in people with high blood pressure on medicines, or with low blood magnesium. For muscle cramps in older adults, a Cochrane review found no clear benefit. Trials for sleep, anxiety and depression are small and low in quality.

How much magnesium do you need?

Adults need 310 to 420 mg of magnesium a day, according to the US Recommended Dietary Allowance (RDA). The RDA covers the needs of nearly all healthy people: it is 400 to 420 mg for men and 310 to 320 mg for women. In the EU, EFSA’s Adequate Intake (AI), a target based on what healthy people eat, is 350 mg for men and 300 mg for women.

In pregnancy, the US allowance is 350 to 360 mg a day at ages 19 to 50 and 400 mg at 14 to 18. For breastfeeding it is 310 to 320 mg (360 mg at ages 14 to 18). EFSA sees only a small rise in need in pregnancy, probably covered by the body’s own adaptation. About 25 mg a day goes into breast milk in the first six months, so EFSA keeps the non-pregnant value for both groups.

For older adults, the US allowance stays at 420 mg for men and 320 mg for women from age 51. EFSA says its values apply to older adults too. The NIH notes that older adults tend to eat less magnesium, absorb less and lose more in urine.

Magnesium deficiency: signs and who is at risk

Early signs of low magnesium are loss of appetite, nausea, vomiting, tiredness and weakness. As it worsens, people can get numbness, tingling, muscle contractions and cramps, and seizures. Personality changes, abnormal heart rhythms and spasms of the heart’s arteries (coronary spasms) can also occur. Severe deficiency can cause low calcium or low potassium, according to the NIH.

These signs are not specific to magnesium. EFSA says nerve or heart symptoms appear when blood magnesium is markedly low, below 0.5 mmol/L (a blood test unit). Supplements have given inconsistent results for cramps, restless legs and fibromyalgia, EFSA adds.

The NIH lists the groups most likely to be low. They include people with gut diseases that cause long-term diarrhea or poor fat absorption, such as Crohn’s disease, celiac disease or small bowel surgery. People with type 2 diabetes, people with alcohol dependence and older adults are also on the list. Long-term use of loop or thiazide diuretics and of proton pump inhibitors can also lower magnesium.

Doctors most often check serum magnesium, where normal is 0.75 to 0.95 mmol/L. But the NIH says it does not reflect total body stores. Other tests exist (red blood cells, urine, a loading test), and none is considered satisfactory on its own. So a low result and a normal result both need a doctor’s reading.

Forms of magnesium: absorption and effects

Magnesium supplements differ in how much magnesium they hold, how well they dissolve and what they do in the gut. The label must show elemental magnesium (the magnesium itself), not the weight of the whole compound, according to the NIH.

The NIH also says forms that dissolve well in liquid are absorbed more completely. In small studies, aspartate, citrate, lactate and chloride were more bioavailable (better absorbed by the body) than oxide and sulfate. A 2017 review concluded that the type of salt matters less than often thought. The dose and your own magnesium status matter more.

The honest bottom line: the human comparisons are small, and they measure absorption, not health. Oxide is the worst absorbed of the forms compared. The NIH lists it among the forms most often reported to cause diarrhea. Citrate and several others are absorbed better.

Glycinate, threonate, malate and taurate have few or no head-to-head human studies. We found no trial that compared forms for sleep, anxiety, cramps or any other outcome. The trials in the benefits section used oxide (constipation, hot flashes), trimagnesium dicitrate (migraine), magnesium chloride (depression) and bisglycinate (sleep, leg cramps in pregnancy).

Form	Share of the mineral by weight	What studies show	Source
Oxide	Not stated	Absorbed poorly: about 4% in one study of healthy volunteers, no better than placebo on blood and urine measures at 300 mg of magnesium a day for 60 days in another, and only 43% dissolved in simulated peak stomach acid. Used in trials of constipation (it worked) and hot flashes (no benefit). The NIH lists it among forms often reported to cause diarrhea.	1, 3, 4, 5, 13, 14
Citrate	Not stated	Raised blood magnesium most in a 60-day trial, and it dissolved and absorbed better than oxide in a second study. Trimagnesium dicitrate at 600 mg a day cut migraine attacks in one trial, with diarrhea in 18.6% of people.	3, 5, 15
Glycinate (bisglycinate, diglycinate)	Not stated	In 12 people with ileal resection, absorption matched oxide overall and was better in the four worst absorbers. One trial of 155 adults with poor sleep found a small gain, and one of 80 pregnant women found fewer leg cramps. No trial compares it with other forms for outcomes, and we found none for anxiety.	6, 11, 12
Chloride and lactate	Not stated	Absorbed about equally to aspartate and far better than oxide in one study. Enteric-coated chloride was absorbed much less than acetate in another. Chloride is also on the NIH list of forms often reported to cause diarrhea. An open-label depression trial used chloride at 248 mg of magnesium a day.	1, 4, 7, 16
Sulfate	Not stated	The NIH says small studies found sulfate less bioavailable than aspartate, citrate, lactate and chloride. Given by drip it is a hospital treatment for pre-eclampsia, not a supplement. A 2017 review found claims for magnesium through the skin, such as Epsom salt baths and sprays, scientifically unsupported.	1, 17
L-threonate	250 mg of magnesium in 3,000 mg of the compound, about 8%	EFSA judged magnesium bioavailable from it, from a dissolution study, two rat studies and one human trial. Rats showed better memory. One human sleep trial of 80 adults is from authors who work for a company. We found no human trial comparing its absorption with other forms.	8, 9, 10
Malate	Not stated	EFSA lists it as allowed in food supplements only. We found no human absorption comparison. The one trial we found used a tablet of malic acid with 50 mg of magnesium for fibromyalgia, and the blinded part showed no clear effect.	2, 18
Aspartate	Not stated	Absorbed about as well as chloride and lactate. In 50 insulin-treated adults, 3 months raised blood magnesium but did not change HbA1c.	4, 19
Taurate and acetyl taurate	Not stated	EFSA lists them as allowed in food supplements only. We found no human absorption comparison or randomized trial.	2

Here are the 12 studies that compare forms or test a single form, strongest evidence first.

Is magnesium safe? Supplements, dose and interactions

Magnesium from food is not a safety concern for healthy people, because the kidneys remove the excess, says the NIH. The US Tolerable Upper Intake Level (UL), the highest daily amount unlikely to cause harm, is 350 mg for adults. It applies only to magnesium from supplements and medicines, not to magnesium found naturally in food and drinks. Medicines such as antacids and laxatives that contain magnesium count toward it too.

For children, the UL is 65 mg at ages 1 to 3 and 110 mg at ages 4 to 8. From age 9 it is 350 mg, including in pregnancy and breastfeeding.

EFSA’s 2015 opinion describes an EU level of 250 mg a day for adults, including pregnant and breastfeeding women, and for children from 4 years. The Scientific Committee on Food set it in 2001, based on mild diarrhea. It covers salts that dissolve easily, such as chloride, sulfate, aspartate and lactate, and compounds such as magnesium oxide. It applies to these in supplements or water, or added to foods.

• Side effects. High doses from supplements or medicines often cause diarrhea, nausea and stomach cramps, the NIH says. That is because unabsorbed magnesium salts pull water into the bowel. In a migraine trial, diarrhea affected 18.6% of people on 600 mg of magnesium as citrate. In a second migraine trial, it affected 45.7% against 23.5% on placebo. Very large doses, usually more than 5,000 mg a day from laxatives or antacids, have caused low blood pressure, irregular heartbeat and cardiac arrest. A few deaths have been reported.
• Kidney disease. The risk of magnesium toxicity rises when the kidneys work poorly, because the body can no longer remove the excess, the NIH says. People with kidney problems should ask a doctor before taking magnesium supplements, antacids or laxatives.
• Drug interactions. Magnesium lowers the absorption of oral bisphosphonates for osteoporosis, so take it at least 2 hours before or after. Tetracycline and quinolone antibiotics should be taken at least 2 hours before or 4 to 6 hours after a magnesium supplement. Loop and thiazide diuretics can deplete magnesium, while amiloride and spironolactone reduce its loss. Very high doses of zinc from supplements (142 mg a day) interfered with magnesium absorption in one study.
• Proton pump inhibitors. The FDA warned in 2011 that prolonged use of these acid-reducing drugs, typically more than a year, can cause low magnesium. In the cases it reviewed, magnesium supplements often fixed the low level. In 25% of cases they did not, and the patients had to stop the drug. A meta-analysis found about 1.7 times the odds of low magnesium in users. Do not stop a prescribed drug on your own.
• Migraine doses. The doses used to prevent migraine, up to 600 mg a day, exceed the upper level. So the NIH says to use them only under a health professional’s direction.

How to get more magnesium

• Best foods. In our ranking, hemp seeds give 210 mg in 3 tablespoons (30 g). Black beans give 120 mg per cup and Brazil nuts 107 mg per ounce. The NIH adds roasted pumpkin seeds at 156 mg per ounce and chia seeds at 111 mg.
• Keep grains whole. Refining removes the germ and bran. Cooked brown rice has 42 mg per ½ cup against 10 mg for white rice, according to the NIH.
• Food and spread-out doses. About half of the magnesium in mineral water was absorbed, and a meal raised it from 45.7% to 52.3%. A 2017 review says the share absorbed is higher when magnesium comes in several small doses than in one large dose. For a supplement, read the elemental magnesium on the label.

Frequently asked questions about magnesium

Does magnesium help you sleep?

The evidence is weak. A meta-analysis of 3 small trials in 151 older adults found people fell asleep about 17 minutes sooner. But every trial had a moderate to high risk of bias.

A 2026 review of 12 trials found inconsistent results and low to very low certainty. It does not support magnesium as a routine treatment for insomnia. One trial of 155 adults taking 250 mg of magnesium as bisglycinate found a small gain (effect size 0.2).

How much magnesium glycinate should I take?

There is no official dose for a specific form, so read the elemental magnesium on the label. The US upper level for supplements is 350 mg of magnesium a day for adults, and the EU level described by EFSA is 250 mg.

The sleep trial used 250 mg of magnesium as bisglycinate for 4 weeks. The pregnancy cramp trial used 300 mg a day of bisglycinate chelate. Higher doses, such as the 600 mg used for migraine, belong under a doctor’s care.

Which magnesium supplement is best?

No form has been shown best for health outcomes. In absorption studies, oxide did worst (about 4% absorbed in one study), while citrate, chloride, lactate and aspartate did better. Glycinate, threonate, malate and taurate lack head-to-head human comparisons. Choose by tolerance and the elemental dose on the label, since oxide and several others can cause diarrhea.

Does magnesium help muscle cramps?

Not in older adults. A Cochrane review of 11 trials found magnesium unlikely to give clinically meaningful relief. It gave 0.18 fewer cramps a week than placebo, a difference that could be chance.

In pregnancy the results conflict. In one trial of 80 women, 86.0% had at least half as many cramps on 300 mg of bisglycinate chelate, against 60.5% on placebo. But the Cochrane review of pregnancy cramps called the evidence inconsistent and low in certainty.

Does magnesium lower blood pressure?

A little. Meta-analyses found systolic pressure (the top number) 2.00 mm Hg lower in 34 trials and 2.81 mm Hg lower in 38 trials. Drops were bigger in people with high blood pressure on medicines (7.68 mm Hg) or with low blood magnesium (5.97 mm Hg). An older Cochrane review called the evidence weak.

In the US, the FDA allows a qualified claim that diets with adequate magnesium may reduce the risk of high blood pressure. The FDA also states that the evidence is inconsistent and inconclusive.

What is the best time to take magnesium?

The sources we used do not name a best time. In a small study, magnesium from mineral water was absorbed better with a meal (52.3% against 45.7%). A 2017 review says several small doses are absorbed better than one large dose.

Keep magnesium at least 2 hours away from bisphosphonates (bone drugs). Take tetracycline or quinolone antibiotics 2 hours before or 4 to 6 hours after magnesium.

Do Epsom salt baths and magnesium sprays work?

There is no good evidence that they do. A 2017 review found the claims for magnesium absorbed through the skin scientifically unsupported. Epsom salt is magnesium sulfate, and the NIH lists sulfate among the less bioavailable forms when swallowed.

Which foods are highest in magnesium?

Hemp seeds lead our USDA ranking: 210 mg in 3 tablespoons (30 g) and 700 mg per 100 g. Soybeans (148 mg per cup), black beans and adzuki beans (120 mg per cup each) and Brazil nuts (107 mg per ounce) follow per serving. Refined grains have much less than whole grains: cooked brown rice has 42 mg per ½ cup against 10 mg for white rice.