Magnesium has become the supplement people take when nothing in particular is wrong. It is sold for sleep, cramp, anxiety, recovery, headaches and energy, usually with the observation that “most people are deficient”. It is worth separating what the reference values say from what the bottles do.
The reference intakes
EFSA sets adequate intakes of 350 mg per day for adult men and 300 mg per day for adult women. Adequate intake rather than population reference intake means EFSA judged the evidence insufficient to derive an average requirement, and instead used observed intakes in apparently healthy populations. That is a weaker kind of number, and worth knowing about before treating it as a threshold to be anxious about.
Where it comes from
Magnesium sits at the centre of the chlorophyll molecule, which is a useful mnemonic: green things have it, and so does most of what grows.
- Seeds — pumpkin seeds are the standout, then sunflower, sesame, chia.
- Nuts — almonds, cashews, brazils.
- Pulses — black beans, white beans, lentils.
- Wholegrains — oats, wholemeal bread, brown rice, buckwheat.
- Leafy greens — spinach, chard.
- Dark chocolate, genuinely, at a decent cocoa percentage.
- Hard water, in some regions, contributes more than people expect.
Refining strips it. White flour loses most of the magnesium of the wheat it came from, and a diet built on refined grains and manufactured food is the realistic route to a low intake — not some modern depletion of the soil, which is the version usually offered.
“Most people are deficient”
This claim conflates two different things. Intakes below the adequate intake are indeed common across Europe. Clinical magnesium deficiency — hypomagnesaemia, with neuromuscular and cardiac consequences — is not common in healthy people, and where it occurs it usually has a cause: chronic alcohol use, malabsorption, poorly controlled diabetes, prolonged diuretic or proton-pump-inhibitor use.
Serum magnesium, incidentally, is a poor test for status, because most of the body’s magnesium is in bone and cells rather than blood. A normal result does not rule much out, which is one reason the “deficiency epidemic” framing is hard to pin down in either direction.
An intake below the adequate intake is not a diagnosis. It is a reason to eat more seeds.
On the forms
The supplement aisle sells magnesium citrate, oxide, glycinate, malate, threonate, taurate and more. Two things are reasonably clear: magnesium oxide is poorly absorbed and is the cheapest and most common filler; the organic salts — citrate, glycinate — are absorbed better. Beyond that, the claims separating one boutique form from another on sleep or anxiety outcomes rest on thin evidence, and the price gap is not proportional to it.
Magnesium’s most reliable and least advertised effect is on the bowel. It draws water into the intestine — which is precisely why magnesium salts are sold as laxatives — and it is the usual reason a high-dose supplement produces an immediate, unmistakable result that has nothing to do with sleep.
A reasonable position
Eat seeds, nuts, pulses and wholegrains often enough that the question does not arise. If you want to take a modest supplement anyway, a few hundred milligrams of a citrate or glycinate is inexpensive and unlikely to do harm in someone with healthy kidneys. Just do not expect it to do the six things on the box, and do not read a marketing claim about widespread deficiency as a clinical statement.
