Magnesium has become the Swiss Army knife of the supplement aisle. It is sold for sleep, stress, muscle cramps, recovery, energy, blood pressure, migraines and general bodily competence. You can swallow it as a tablet, stir it into water, spray it onto your legs or soak in a bath full of it.

Which raises a fair question: what is the best way to take magnesium?

The useful answer is less glamorous than the marketing. For most people, magnesium-rich food comes first. If you need a supplement, an oral form such as magnesium citrate or glycinate is the most practical and evidence-based choice.

Powders do not appear to beat pills containing the same form and dose. Magnesium sprays and baths may feel pleasant, but there is little evidence that they deliver clinically useful amounts of magnesium through your skin.

What does magnesium actually do?

Magnesium is an essential mineral. Your body cannot manufacture it, so you need to obtain it from food or supplements.

It is involved in more than 300 enzyme systems and plays a part in energy production, protein synthesis, muscle contraction, nerve signalling, blood-pressure regulation, glucose control and normal heart rhythm.

About 50–60 per cent of the magnesium in your body is stored in bone. Most of the rest sits in muscle and other soft tissues. Only about one per cent is found in the blood.

That matters because a normal blood test does not necessarily prove that your overall magnesium stores are perfect. Serum magnesium is useful for identifying serious deficiency, but it is a relatively blunt tool for measuring total-body status.

It also means that every ordinary ache, twitch or bad night’s sleep should not automatically be diagnosed as magnesium deficiency. Fatigue, cramps and poor sleep can have dozens of causes.

How are magnesium supplements made?

Supplement labels can make magnesium look more complicated than it is.

Magnesium is usually bound to another substance to form a salt or chelate. That produces names such as:

• Magnesium citrate
• Magnesium oxide
• Magnesium chloride
• Magnesium glycinate
• Magnesium lactate
• Magnesium sulphate

The number on the front of the bottle can be misleading. A product containing 500 mg of a magnesium compound does not necessarily provide 500 mg of elemental magnesium. Elemental magnesium is the amount of magnesium itself. That is the figure that matters when comparing products and doses.

Manufacturers form the magnesium compound, purify and dry it, then place it into capsules, press it into tablets or sell it as powder. Flavours, coatings, fillers and anti-caking agents may also be added.

What is the best-absorbed form of magnesium?

No single magnesium form has been conclusively crowned world champion. However, some forms are better supported than others. A randomised study comparing magnesium citrate, oxide and an amino-acid chelate found citrate produced the strongest markers of absorption over 60 days. Other research has also found citrate more soluble and better absorbed than oxide. You can read the study on PubMed.

Magnesium citrate

Citrate is one of the better-studied forms and is generally well absorbed. It is a sensible all-purpose choice. The catch is that it can draw water into the bowel, particularly at higher doses. That makes it useful for constipation but potentially inconvenient before a long run, work meeting or interstate flight.

Magnesium glycinate

Magnesium glycinate, also called bisglycinate, is magnesium bound to the amino acid glycine. It is widely promoted as the best form for sleep and anxiety. The evidence is not strong enough to support that claim with much confidence.

Its clearer advantage is tolerance. Glycinate tends to be gentler on the stomach and less laxative than citrate or oxide. That makes it a reasonable choice for anyone who finds other forms difficult to handle.

Magnesium oxide

Oxide contains a high percentage of elemental magnesium and is usually cheap. Unfortunately, it is poorly soluble and tends to be less well absorbed than citrate, chloride, lactate or glycinate.

It is also more likely to cause diarrhoea.

Magnesium oxide is not useless. It works perfectly well when the desired result is a laxative effect. It is simply a weaker choice when the main goal is efficient magnesium supplementation.

Are powders absorbed better than tablets?

Probably not in any meaningful way.

A powder dissolved in water may begin dissolving sooner because the tablet does not need to break apart first. That does not necessarily mean more magnesium is absorbed overall.

The magnesium compound, elemental dose, solubility and your digestive system matter more than whether the product arrives as powder, capsule or tablet.

A properly manufactured tablet containing 200 mg of elemental magnesium citrate should deliver a broadly similar amount to 200 mg of magnesium citrate dissolved in water.

Choose powder because you prefer drinking it or have trouble swallowing tablets. Do not pay extra because the label claims “instant” or “superior” absorption without showing evidence.

Do magnesium sprays and baths work?

This is where the marketing gets ahead of the science. Magnesium oil is not actually an oil. It is generally magnesium chloride dissolved in water. It feels oily when rubbed onto the skin, hence the name. The claim is that magnesium passes through the skin, bypasses the digestive system and enters the bloodstream faster than oral magnesium.

The problem is that intact human skin is designed to keep things out. A review published in Nutrients concluded that claims promoting transdermal magnesium were scientifically unsupported. You can read it on PubMed.

One small pilot study tested a cream providing 56 mg of magnesium daily for two weeks. It included only 25 people and did not find a significant overall increase in serum magnesium. A significant result appeared only after the researchers analysed a smaller subgroup. That is nowhere near enough evidence to treat magnesium cream as a reliable delivery method. The study is available on PubMed.

The same caution applies to Epsom-salt baths. A warm bath may relax you. It may reduce your sense of muscle tension. It may help you slow down before bed. None of that proves magnesium has entered your bloodstream in a meaningful amount. Take the bath because baths are good. Do not rely on one to correct a magnesium shortfall.

Does magnesium help you sleep?

Possibly, but expectations should remain modest. A systematic review of three trials involving 151 older adults found magnesium shortened the time taken to fall asleep by about 17 minutes. However, the evidence was rated low to very low quality, and the studies were small and at risk of bias.

The review can be read on PubMed. That is not the same as showing that every healthy adult will sleep better after taking magnesium glycinate before bed.

Magnesium may be more useful when someone has low intake, a genuine deficiency or a specific sleep problem. It is not a reliable substitute for regular sleep hours, less alcohol, lower evening caffeine intake or putting the phone down.

What about muscle cramps and recovery?

Magnesium is essential for normal muscle function. That biological fact is often turned into the assumption that extra magnesium must prevent cramps. The trials do not support that leap.

A Cochrane review of 11 studies found magnesium was unlikely to produce a meaningful reduction in muscle-cramp frequency or severity in older adults. Evidence in pregnancy was less certain. You can read the review here.

That does not mean magnesium can never help a cramp. It may help when the cramp is related to an actual deficiency. But most exercise cramps are more complicated than one missing mineral.

Fatigue, training load, previous cramping, heat, hydration and neuromuscular factors may all be involved.

Where is the evidence stronger?

Magnesium unquestionably helps treat diagnosed deficiency. It also has a reliable laxative effect in forms such as citrate, oxide and hydroxide.

The evidence for blood pressure is reasonably encouraging but not dramatic. A large meta-analysis found magnesium supplementation reduced systolic blood pressure by about 2.8 mmHg and diastolic pressure by about 2.1 mmHg on average. Benefits tended to be larger in people with hypertension or low magnesium status.

There is also some evidence that high-dose oral magnesium may help prevent migraines, although results are mixed and gastrointestinal side effects become more common at the doses used. In other words, magnesium may have useful clinical effects. It is not magic mineral dust.

How should you take it?

Start with food. When using a supplement, check the amount of elemental magnesium rather than the total compound weight.

Citrate is a solid choice when absorption is the priority and your stomach tolerates it. Glycinate is a reasonable option when you want something gentler on the gut.

Taking magnesium with food may reduce stomach upset. Splitting a larger daily amount into two smaller doses may also improve tolerance.

Be careful if you have kidney disease. Healthy kidneys remove excess magnesium, but impaired kidneys may allow it to accumulate to dangerous levels.

Magnesium can also interfere with the absorption of some antibiotics, bisphosphonates and thyroid medication. Proton-pump inhibitors and some diuretics can affect magnesium status. Check with a pharmacist before combining supplements with regular medication.

And the Verdict is…

The best way to take magnesium is not through your skin. It is through food, followed by a sensible oral supplement when needed.

Magnesium citrate has some of the strongest evidence for absorption. Glycinate may be easier on the stomach. Oxide is cheap but poorly absorbed and more likely to send you looking for the nearest toilet. Powder is not automatically better than a pill. Baths and sprays are not proven methods of correcting low magnesium. And unless you are deficient, magnesium may not transform your sleep, recovery or life.

Sometimes a supplement fills a genuine gap. Sometimes it is just an expensive way to make your evening water taste faintly of lemon.