Magnesium supplements: worth taking? Cramps, sleep, stress, migraine: what the studies really show

Daniel Platteau

In short: magnesium is essential, but a varied diet usually provides enough. For cramps in older people, trials show it is probably useless. For sleep, the effect is small and the evidence weak. It has a recognised place in migraine prevention, it lowers blood pressure slightly, and magnesium oxide is a real laxative. The "reduces tiredness" statements on the packs are allowed for any product that contains a little of it: they do not prove the supplement will help you.

What does magnesium do?

An adult body contains about 25 grams of magnesium, half or slightly more of it in the bones. The rest is mostly inside cells, especially in the muscles. The blood holds only a tiny fraction, less than 1%.

By mass, it is the eleventh most abundant element in the human body ("Magnesium", 2026). Every cell needs it: in particular, it acts as a cofactor for some 300 enzymes, a helper without which they cannot work. It also binds to phosphate-rich molecules such as ATP, which carries energy inside cells, DNA and RNA. This is how it takes part in energy production, protein building, nerve and muscle function, heart rhythm and bone strength. This very broad role fuels the marketing: since it is involved everywhere, it gets credited with effects on everything. But the fact that a nutrient is essential does not mean that adding more, when you already have enough, brings any benefit.

How much do you need?

In 2015, the European Food Safety Authority (EFSA) set an adequate intake of 350 mg a day for men and 300 mg for women (EFSA, 2015). On labels, the European reference value is 375 mg.

It is found mainly in minimally processed foods:

nuts: a small handful of almonds (28 g) provides about 80 mg;
green vegetables: half a cup of cooked spinach, about 78 mg;
pulses: half a cup of cooked black beans, about 60 mg;
whole grains, dark chocolate, some mineral waters.

These figures come from the US National Institutes of Health tables (NIH ODS, 2026). A diet rich in whole grains, vegetables and pulses therefore covers needs easily. A diet made mostly of refined products, much less so.

Water counts too. In the EU, a mineral water may carry the statement "contains magnesium" above 50 mg per litre (Directive 2009/54/EC). Some contain much more, such as the French water Hépar (119 mg per litre): 1.5 litres then provide about 180 mg, half of a man's needs. Being very rich in sulphates, this water is also a laxative (Vidal, n.d.).

Who may run short?

True magnesium deficiency is rare in a healthy person, because the kidneys can reduce losses when intake drops. The risk rises in a few well-known situations (NIH ODS, 2026):

digestive diseases that hinder absorption, such as Crohn's disease or coeliac disease;
poorly controlled type 2 diabetes, which increases magnesium loss in urine;
excessive alcohol consumption;
older people, who absorb less and excrete more;
some medicines: diuretics and proton pump inhibitors (PPIs), the drugs for stomach acid (omeprazole, pantoprazole, esomeprazole…). Taken for months, often more than a year, they can make magnesium drop. Medicines regulators recommend measuring it before and during prolonged treatment, especially in people also taking digoxin or diuretics (MHRA, 2014).

Are intakes often too low? A European study compared the national food surveys of eight countries, including Belgium, with the estimated average requirement (Mensink et al., 2013). Depending on the country and age group, diet alone (without supplements) fell short of this requirement in up to 59% of women aged 14 to 50 and up to 44% of men over 60, the highest figures coming from the United Kingdom. An intake below this benchmark raises the risk of a shortage, but does not prove it: the kidneys partly compensate, and a real deficit remains uncommon outside the diseases and medicines listed above (Nordic Council of Ministers, 2023).

What about the "3 in 4 French people short of magnesium" from the SU.VI.MAX study? This widely repeated figure comes from the food records of participants in the French SU.VI.MAX study in the mid-1990s: about 72% of men and 77% of women were below the French recommended intakes of the time. Those benchmarks were higher than today's values, and being below a recommended intake does not mean lacking magnesium. The original publication is also hard to find. SU.VI.MAX is best known for its trial of antioxidant supplements run from 1994 to 2002: fewer cancers in men, no effect in women (Hercberg et al., 2004). It is a serious study, often cited, and often cited wrongly, in both directions.

The signs of a real shortage are not specific: loss of appetite, nausea, tiredness and weakness at first, then tingling, muscle contractions and cramps, and heart rhythm problems as it worsens (NIH ODS, 2026). None of these signs on its own proves a magnesium shortage: a twitching eyelid or a bout of tiredness has many other, far more common causes.

One difficulty: a blood test reflects stores poorly. Blood magnesium is only a tiny part of the total, and the body keeps its level stable for as long as it can. A normal result therefore does not rule out a moderate shortfall. A low level, on the other hand, confirms a shortage, whose cause should be looked for with a doctor.

What the studies show, problem by problem

Cramps: probably useless

This is the number one selling point. A Cochrane review, the gold standard in this field, pooled 11 randomised trials and 735 participants (Garrison et al., 2020). In older people with night cramps and no particular cause, magnesium probably does no better than a placebo: not on the number of cramps, nor on their duration, nor on their intensity. For cramps during pregnancy, the results are contradictory and the evidence is of very low quality. For exercise-related cramps, no usable study was found.

Level of evidence: systematic review of controlled trials, moderate to high certainty for older people.

Sleep: a small effect, weak evidence

A 2021 meta-analysis found only three small trials in older people with insomnia, 151 participants in all (Mah & Pitre, 2021). Magnesium shortened the time to fall asleep by about 17 minutes, with no significant effect on total sleep time. The authors rate these trials at moderate to high risk of bias and the quality of evidence as low to very low.

A more recent trial in 155 adults who slept poorly tested 250 mg of magnesium a day as bisglycinate for four weeks (Schuster et al., 2025). The insomnia score improved slightly more than with placebo, but the gap was small: 1.6 points on a scale that goes up to 28.

Level of evidence: a few controlled trials, small or with a modest effect. If you try it, expect at best a slight help, not a sleeping pill.

Migraine: the most serious lead

This is the area where magnesium has the most credibility. Several double-blind trials tested high doses, generally 600 mg of magnesium a day as dicitrate, for several weeks to reduce how often attacks occur. That is more than twice the limit advised for supplements (see below): so this is not self-medication. A systematic review concludes that this strategy is safe and inexpensive, with a level of evidence rated "possibly effective" (von Luckner & Riederer, 2018). Neurology societies list it among the preventive treatments that can be considered.

Level of evidence: controlled trials, positive but modest results. At these doses diarrhoea is common, and preventive migraine treatment should be discussed with your doctor.

Blood pressure: a modest drop

A meta-analysis of 34 trials and 2,028 participants found that about 370 mg of magnesium a day for three months on average lowered blood pressure by 2 mmHg systolic and 1.8 mmHg diastolic (Zhang et al., 2016). That is real but small: less salt, physical activity or treatment do much more. The authors suggest the effect may be limited to people who are short of magnesium.

Level of evidence: meta-analysis of controlled trials, modest effect.

Constipation: here it works

No doubt here: at high doses, magnesium draws water into the bowel. Magnesium oxide is in fact used as a laxative. In a Japanese trial of 90 patients with chronic constipation, 1.5 g of magnesium oxide a day for 28 days improved symptoms in 68% of patients, against 12% on placebo (Morishita et al., 2021).

This is also why diarrhoea is the most common side effect of magnesium supplements.

Stress, fatigue, anxiety, "anti-aging"

For stress and anxiety, the available studies are few, small and of poor quality. You also read that stress "drains" the body of magnesium. In animals and in a few small human studies (exam periods, exposure to noise), stress does increase losses in the urine, but only temporarily; the idea of a "vicious circle" between stress and magnesium shortage remains a hypothesis (Pickering et al., 2020, a review two of whose authors work for a supplement maker). For an "anti-aging" effect, nothing has been shown in people who are not short of magnesium: this is what we already concluded in our ranking of anti-aging supplements. Magnesium compounds are also real medicines: laxatives, antacids such as milk of magnesia (magnesium hydroxide) and, in hospital, given intravenously, the reference treatment for eclampsia, a serious complication of pregnancy: it cuts its risk by more than half (Magpie Trial Collaborative Group, 2002). These uses say nothing about the effect of the capsules sold in pharmacies in a healthy person.

"Contributes to the reduction of tiredness": what the claims mean

On almost every pack, you read that magnesium "contributes to the reduction of tiredness and fatigue", "to the normal functioning of the nervous system" or "to normal muscle function". These statements are legal: they appear on the list of health claims authorised in the European Union (Commission Regulation (EU) No 432/2012).

But they describe the role of magnesium in the body, not the effect of a supplement in someone who already has enough. They are allowed for any food that contains at least 15% of the reference value, about 56 mg per serving. A handful of almonds would qualify. So these statements do not tell you that a supplement will fix your tiredness.

Oxide, citrate, bisglycinate, threonate: does the form matter?

Magnesium is always sold bound to another molecule, and what counts is the amount of elemental magnesium shown on the label, not the weight of the salt.

Oxide: rich in magnesium and cheap, but less well absorbed and more laxative. In a 60-day trial in 46 adults, citrate was better absorbed than oxide (Walker et al., 2003).
Citrate: well absorbed, somewhat laxative at high doses.
Bisglycinate (or glycinate): often presented as gentler on the gut. Rigorous comparisons with citrate remain rare.
Threonate: sold for the brain. A six-week trial in 100 adults found a small improvement in cognitive tests (Lopresti & Smith, 2026). It is a single trial, on a branded product, in young adults, and it provides little magnesium: 145 mg a day. To be confirmed.
Chloride, lactate, malate, pidolate: common forms, with no proven advantage over one another for ordinary use.

In practice, if a supplement is justified, citrate or bisglycinate are reasonable choices. Paying much more for a "special" form rests mostly on marketing. Also be wary of "complexes" that add vitamins to the magnesium: they bring no proven benefit and make doses harder to work out.

Side effects, overdose and interactions

Magnesium from food poses no problem: the kidneys get rid of the excess. Magnesium from supplements, on the other hand, has a limit. In 2001, the EU Scientific Committee on Food set 250 mg a day as the amount of magnesium not to exceed from supplements (or added to water and foods), because of the risk of diarrhoea. Magnesium naturally present in food is not counted (EFSA, 2025).

The real dangers mainly concern:

kidney failure: the kidneys can no longer get rid of the excess, and magnesium can build up to the point of causing weakness, a drop in blood pressure or heart rhythm problems. No supplement without medical advice in this case;
very high doses of laxatives or antacids containing magnesium, taken over a long period (NIH ODS, 2026).

Magnesium also hinders the absorption of some medicines. Doses need to be spaced out (NIH ODS, 2026):

bisphosphonates for osteoporosis: at least 2 hours apart;
antibiotics of the tetracycline or quinolone families: take the antibiotic at least 2 hours before or 4 to 6 hours after the magnesium.

In practice

Start with your plate: pulses, nuts, green vegetables and whole grains cover the needs of most people.
Situations where a supplement may be discussed: frequent migraines, constipation, long-term PPI or diuretic treatment with a low level, digestive disease, excessive alcohol consumption.
For night cramps, magnesium is unlikely to help: stretching, and seeing a doctor if they are frequent, are more useful.
If you take it, stay at 250 mg of elemental magnesium a day unless your doctor advises otherwise (the higher doses used for migraine are taken under supervision), and look at what is written on the label, not at the promise. The 300 to 400 mg a day "courses" often advised online exceed this limit.

For the other supplement most sold in winter, see vitamin D in winter. For an overview of vitamins and minerals, see our article on vitamins and trace elements (in French).

Test yourself

Disclaimer

This article is an information summary. It does not replace the advice of a doctor or pharmacist, especially in case of kidney disease, long-term treatment, pregnancy or persistent symptoms.

Sources

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