Magnesium: which form, how much, and who needs it

You are standing in front of a shelf with oxide, citrate, bisglycinate, malate and three more names you have never seen, and the cheapest tub costs a third of the dearest one. The question is whether you need magnesium at all, and if so, in which form. That depends on how much you already get from food and what you expect it to fix.

What magnesium does, and where it stops

Magnesium is a cofactor in hundreds of enzyme reactions. It is involved in producing ATP, building proteins, carrying nerve signals and — the part lifters care about — letting a muscle fibre relax after it contracts. Calcium drives the contraction; magnesium helps the fibre settle back down.

That long list of jobs gets used as an argument that everyone should supplement. It does not follow. If your intake is already adequate, those reactions are running normally and another 400 mg will not speed them up.

The honest case for a supplement is narrow: your intake from food is regularly short. Then you are filling a gap, not upgrading a healthy system.

How much you need, and where it comes from

Adult intake recommendations sit around 310–320 mg a day for women and 400–420 mg for men. Training pushes the requirement up slightly, since some magnesium is lost in sweat and urine, but the extra is small and food covers it easily.

The densest sources are pumpkin seeds, almonds, cashews, sunflower seeds, dark chocolate with a high cocoa content, beans, chickpeas and lentils, wholegrain bread and cereals, spinach and chard. A handful of nuts, a plate of beans and a couple of squares of dark chocolate get most people close to the target inside a single day.

The catch is that a diet built on white flour, meat and dairy leaves plenty of people below that figure. It is rarely a dramatic deficiency — more often a mild, steady shortfall that nobody notices.

The forms, and what really separates them

Two things distinguish one form from another: how much elemental magnesium sits in a gram of powder, and how much of it your gut absorbs. The second matters more, and the label almost never mentions it.

Oxide

Cheapest and most concentrated, at roughly 60 per cent elemental magnesium by weight. Absorption is poor, so much of it stays in the bowel, draws in water and acts as a laxative. Useful if constipation is your problem, weak if raising your levels is.

Citrate

Around 16 per cent elemental magnesium, but absorbed far better than oxide. It is the sensible default and the best value for money. At larger doses it still loosens stools, which some people count as a benefit.

Bisglycinate (glycinate)

Magnesium bound to the amino acid glycine, around 14 per cent elemental. It is the gentlest on the stomach, which is why it is the usual pick for people taking it in the evening or with a touchy gut.

Malate, taurate, threonate, chloride

Malate is sold with a story about energy and fatigue, taurate for the heart, threonate for memory and focus. The evidence behind those specific claims is thin — small or preliminary work at best. They are not bad forms; you are paying for a promise that has not been settled.

Epsom salts are magnesium sulphate, and a hot soak genuinely feels good, but the idea that meaningful amounts cross the skin is poorly supported. If a bath after training helps you, the heat is doing the work — what the measurements show after saunas and hot baths is worth reading on its own.

What the evidence supports, and what it does not

The strongest evidence is also the least exciting: correcting a low intake. Fix a real shortfall and people report fewer cramps, steadier sleep and less eyelid twitching.

For sleep, the evidence is moderate and mostly in people who sleep badly or eat poorly to start with. If you already get your seven or eight hours, magnesium has little to add.

For leg cramps the picture is weaker than the marketing suggests, particularly for night cramps in older adults, where trials have largely come up empty. For migraine prevention and for small reductions in blood pressure the evidence is firmer, but both belong in a conversation with a doctor rather than a decision made in front of a shelf.

On performance the answer is blunt: if you are not short of magnesium, it will not buy you a single rep. That is the gap between it and creatine, where the effect on strength and training volume rests on far firmer ground, so it is worth knowing what dose to use and whether a loading phase helps. Magnesium is not a stimulant either; the alertness people are chasing comes from caffeine, which is a separate discussion about what coffee and pre-workout actually do. As with collagen and joints, the useful habit is separating what the research shows from what the tub claims.

Taking it without upsetting your stomach

Typical supplemental doses run 200–400 mg of elemental magnesium a day. The commonly cited upper limit for supplemental magnesium in adults is about 350 mg a day; magnesium from food is not counted, because healthy kidneys clear the excess without trouble.

In practice: split the dose in two, take it with a meal, and start low before working up. Loose stools are the first sign you have overshot, and that is a signal to cut back rather than push through.

Timing is not critical. The evening makes sense if it helps your sleep and the form agrees with you. One real trap: magnesium can reduce the absorption of tetracycline and quinolone antibiotics and of levothyroxine, so leave a few hours between them.

When to see a doctor

A blood test for magnesium tells you less than it appears to, because only a small fraction of the body's magnesium sits in the blood. A normal result does not rule out a low intake.

Speak to a doctor before supplementing if you have kidney disease — magnesium can build up, and doses that are harmless for others are not harmless for you. The same applies if you take diuretics, heart medication or proton pump inhibitors long term, if you have persistent cramps alongside tingling or weakness, or if fatigue and poor sleep drag on for months despite decent food and sensible training.

The short version

• Magnesium helps when you are short of it; beyond that it adds nothing to strength or endurance.
• Aim for roughly 310–320 mg a day for women and 400–420 mg for men; seeds, nuts, beans and wholegrains cover it without a tub.
• Citrate is the best value for everyday use, bisglycinate the gentlest on the gut, oxide mostly a laxative.
• 200–400 mg of elemental magnesium with food, split across the day; loose stools mean the dose is too high.
• Kidney disease, long-term medication or cramps with tingling — ask a doctor before you buy.