Magnesium: What It Really Does

Magnesium is one of the most abundant minerals in the human body, involved in more than 300 enzymatic reactions ⁸. The European Union has authorised specific health claims for magnesium under Regulation (EC) 1924/2006 ²: it contributes to normal muscle function, normal electrolyte balance, reduction of tiredness and fatigue, and normal functioning of the nervous system ¹. These claims are not marketing — they are EU-regulated statements backed by assessed scientific evidence. The honest catch: if you eat a reasonably varied diet, you are probably not deficient, and a supplement is unlikely to do much ³.

What magnesium actually does: the EU-authorised evidence

The EU Health Claims Register lists magnesium among a small group of nutrients with firmly established, authorised Article 13.1 claims ¹². These are claims that survived EFSA's scientific review process — which means the evidence was judged sufficient to conclude a genuine physiological relationship exists. Specifically for magnesium, the four authorised areas are:

Normal muscle function — magnesium is essential for both contraction and relaxation of skeletal and smooth muscle ⁸.
Normal electrolyte balance — magnesium works alongside sodium, potassium and calcium to regulate fluid and ion movement across cell membranes ⁸.
Reduction of tiredness and fatigue — magnesium is required for ATP production (the cellular energy currency), so low levels may impair energy metabolism ⁹.
Normal functioning of the nervous system — magnesium modulates ion channels and neurotransmitter activity throughout the nervous system ⁸¹¹.

EFSA also set dietary reference values for magnesium in 2015, recommending 350 mg/day for men and 300 mg/day for women ⁵. These figures are used by EU member states as the basis for national guidelines. The US RDA is slightly higher at 400–420 mg for men and 310–320 mg for women ³. Both reflect the same underlying science — minor methodological differences in how reference values are derived account for the small gap.

When the evidence is thin: night cramps and the Cochrane verdict

Here is the "quando è inutile" part — and this matters because magnesium is heavily marketed for nocturnal leg cramps. The best available evidence does not support this use.

A 2020 Cochrane systematic review by Garrison and colleagues pooled 11 randomised controlled trials enrolling 735 participants across different clinical settings — older adults with idiopathic cramps, pregnant women, and a small group with liver cirrhosis ⁴. For idiopathic cramps (the kind most adults get at night), the results were clear: differences in cramp frequency between magnesium and placebo were small, not statistically significant, and showed minimal variability across studies (I² = 0–12%). The proportion of people achieving a clinically meaningful 25% reduction in cramp rate was no different between magnesium and placebo (high-certainty evidence) ⁴. The authors' conclusion: "It is unlikely that magnesium supplementation provides clinically meaningful cramp prophylaxis to older adults experiencing skeletal muscle cramps."

The picture for pregnancy-associated cramps was conflicting — some trials found benefit, others did not — and the overall quality of those studies was lower, so no firm conclusion either way is possible ⁴. For exercise-associated cramps, no RCT data existed at all.

Who plausibly benefits from supplementation

The caveat here is important: the question is not whether magnesium matters — it clearly does — but whether supplementation on top of a normal diet provides any additional benefit to healthy adults. For most, the answer is no. There are, however, groups where true insufficiency is plausible ³⁹¹¹:

People with gastrointestinal conditions that reduce absorption — Crohn's disease, coeliac disease, chronic diarrhoea ³.
People with type 2 diabetes, where urinary magnesium loss is increased ³⁹.
Older adults, who both absorb less magnesium from food and excrete more through the kidneys ³.
People with long-term heavy alcohol use, which reduces magnesium absorption and increases renal loss ³.
People taking certain medications for extended periods — proton pump inhibitors (PPIs), some diuretics, and certain antibiotics — which interfere with magnesium retention or absorption ³.
Heavy endurance athletes with high sweat losses may have increased requirements, though evidence for supplementation specifically in this group is limited ⁹.

If you fall into one of these categories, the right first step is a blood test and a conversation with your doctor or pharmacist — not a trip to the supplement aisle. Serum magnesium alone is an imperfect marker (most body magnesium is intracellular), but it is the standard starting point ⁸.

Food first: the best sources of magnesium

If you want to improve your magnesium status, eating more of the following foods is both effective and far cheaper than supplements. Values are approximate per 100 g, based on USDA FoodData Central data ⁷:

Food	Mg per 100 g (approx.)
Pumpkin seeds (raw)	~530 mg
Dark chocolate (70–85% cocoa)	~228 mg
Almonds (raw)	~270 mg
Boiled spinach	~87 mg
Cooked black beans	~70 mg
Cooked lentils	~36 mg

A small handful of pumpkin seeds (30 g) provides around 160 mg — roughly half the EFSA reference intake for women. Dark chocolate and almonds are similarly dense. The point is that a varied diet built around whole foods, legumes, nuts and leafy greens will meet most people's magnesium needs without any supplement.

If you do take a supplement: a brief note on forms

Not all magnesium supplements are equal in how well the body absorbs them. Research consistently shows that organic salts — magnesium citrate, lactate and aspartate — are better absorbed than magnesium oxide ³⁶. A randomised trial by Walker et al. found magnesium citrate to be significantly more bioavailable than magnesium oxide, with citrate achieving higher serum and urinary magnesium levels after equivalent doses ⁶. Oxide is cheap and dominates pharmacy shelves, but its bioavailability has been measured at roughly 4% in some studies versus 25–30% for citrate ⁶. In practice, a high dose of oxide mainly functions as a laxative — which partly explains the gastrointestinal side effects seen in the Cochrane trials.

The EU tolerable upper intake level for supplemental magnesium in adults is 250 mg/day ⁵. Above this threshold, diarrhoea and gastrointestinal discomfort become increasingly likely. Food-derived magnesium is not subject to this limit — the kidneys handle dietary excess efficiently in healthy adults.

The bottom line

Magnesium is a genuinely important mineral with four well-evidenced, EU-authorised roles. If you eat a varied diet and have no specific medical reason to believe your levels are low, a supplement is unlikely to do anything useful — and for the most popular use case (night cramps), the best evidence says it probably doesn't work. If you are in a higher-risk group or taking medications that affect magnesium retention, talk to your doctor rather than self-supplementing. And if you simply want more magnesium, eat more seeds, nuts, legumes and leafy greens.

Already taking supplements for pain or joints? Bring the bottles to your first visit — we'll review them together, no extra cost and nothing to sell you.

FAQ

What does magnesium actually do in the body?

Magnesium contributes to normal muscle function, normal electrolyte balance, normal functioning of the nervous system, and reduction of tiredness and fatigue — these are the claims authorised by the European Union under Regulation (EC) 1924/2006 ¹². Beyond these confirmed roles, it is also involved in protein synthesis, bone maintenance, and energy metabolism, and the body uses it in over 300 enzymatic reactions ³.

Does magnesium help with night cramps?

Probably not for most adults. A 2020 Cochrane systematic review (Garrison et al., 11 trials, 735 participants) found that magnesium supplementation is unlikely to provide clinically meaningful cramp prophylaxis to older adults with idiopathic skeletal muscle cramps, with moderate-to-high certainty evidence ⁴. The results for pregnancy-associated cramps were conflicting and inconclusive. Save your money unless your doctor has a specific reason to suggest otherwise.

How much magnesium do I need per day, and what is the tolerable upper limit?

Adult men need around 400–420 mg/day; adult women around 310–320 mg/day (US RDA, NIH ODS) ³. In the EU, the tolerable upper intake level (UL) from supplements specifically is 250 mg/day for adults — amounts above this from supplemental sources may cause diarrhoea and gastrointestinal upset ⁵. Food-derived magnesium carries no such upper limit because healthy kidneys excrete any excess.

Which form of magnesium supplement is best absorbed?

Organic forms such as magnesium citrate, lactate, and aspartate are generally better absorbed than inorganic forms such as magnesium oxide ³⁶. Oxide delivers a higher absolute mg per tablet (cheap and widely sold) but has lower bioavailability — roughly 4% in some studies versus around 25–30% for citrate ⁶. If you and your doctor decide a supplement is warranted, citrate is a reasonable choice; oxide mainly works as a laxative.

Can I get enough magnesium from food alone?

Yes, for most healthy adults eating a varied diet. Good sources include pumpkin seeds (~530 mg/100 g), almonds (~270 mg/100 g), boiled spinach (~87 mg/100 g), dark chocolate (~228 mg/100 g), and cooked legumes such as black beans (~70 mg/100 g) ⁷. A handful of pumpkin seeds or a palm of almonds a day covers a substantial fraction of daily needs without any supplement.

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Magnesium: what it actually does (and when it's useless)