Magnesium: which form to take, how much, and what actually works

The pattern is familiar enough that it is worth naming plainly. Someone buys magnesium because a friend or a pharmacist suggested it, takes it for three or four weeks, notices nothing at all, and concludes that magnesium is one of those things that works for other people.

Almost always, one of two things has gone wrong, and often both.

The form was wrong. Magnesium is never sold on its own. It is always bound to something, and what it is bound to changes how much of it crosses your gut wall. The cheapest option to manufacture is magnesium oxide, which also happens to carry a lot of magnesium by weight, so it produces a large, impressive number on the front of the tub. Very little of that number reaches you.

The amount was too small. When we were looking at what was on the shelf in New Zealand before we made this product, the serving recommendations we were reading were typically 100 to 200mg of elemental magnesium a day. That is a fraction of what the balance research suggests an adult needs, and it is not enough to shift a level in someone who is genuinely low.

Neither of those is a reason to give up on magnesium. They are reasons to read a label differently, which is what the rest of this guide is for. If you want the short version of how to do that, we have a separate piece on what separates a good magnesium supplement from a cheap one.

This is the single most useful thing to understand before you buy anything, and it is the thing labels are least clear about.

Magnesium is a mineral bound to a carrier. Magnesium citrate is magnesium plus citric acid. Magnesium glycinate is magnesium plus glycine. In every case, the compound weighs considerably more than the magnesium inside it, and the fraction that is actually magnesium is called the elemental magnesium.

Take our own label as the worked example. One scoop contains 1000mg of magnesium citrate. The elemental magnesium in that 1000mg is 150mg. The other 850mg is citric acid, which is doing its own useful work but is not magnesium.

So when a product front reads "1000mg magnesium", the honest question is 1000mg of what. If the elemental figure is not printed anywhere, that is usually deliberate. A well-made product prints both numbers because both are worth knowing.

The clearest single number in this whole area comes from a 2001 study that measured the bioavailability of four commercially available magnesium preparations by tracking how much extra magnesium volunteers excreted in their urine after taking each one.

Magnesium oxide came out at a fractional absorption of about 4 per cent. Magnesium chloride, lactate and aspartate were all significantly higher, and equivalent to each other. The authors' conclusion was that oxide is relatively poorly absorbed and that inorganic salts are not automatically worse than organic ones, which is a more interesting finding than the one usually quoted from this paper.

Four per cent is the figure worth carrying. It means that a tablet promising 500mg of magnesium as oxide is, on those numbers, delivering something in the region of 20mg. That is not a marketing exaggeration on the manufacturer's part. The magnesium is genuinely in the tablet. It just does not get in to you.

Absorption percentages for every form do not exist. Anyone who shows you a neat bar chart with a number against citrate, glycinate and oxide has made most of those numbers up, and that is worth saying because those charts are everywhere.

What does exist is a direct comparison. In 2003 a team at the University of Reading ran a randomised, double-blind, placebo-controlled trial in 46 healthy adults, comparing magnesium oxide, magnesium citrate and an amino acid chelate at 300mg of elemental magnesium a day for 60 days. They measured magnesium in blood, urine, saliva and red blood cells, at 24 hours and again at 60 days.

Three findings are worth pulling out.

Both organic forms, citrate and the amino acid chelate, showed greater absorption than oxide at 60 days as measured by urinary excretion. Magnesium citrate produced the highest mean blood magnesium of any group, at 24 hours and again at 60 days, and the highest salivary magnesium at 60 days. And magnesium oxide produced no difference compared with placebo, on any measure the trial looked at.

That last sentence is the one that should change how you shop. Not that oxide is worse. That over 60 days, in this trial, it was indistinguishable from taking nothing.

One scoop carries 400mg of elemental magnesium, split across chelate, citrate and malate. The split is not decoration. What the magnesium is bound to has effects of its own, so choosing three carriers means choosing three sets of effects.

The glycinate is the clearest example of why the carrier matters. Glycine is an amino acid with its own calming and sleep-related effects, independent of the magnesium it is attached to. Bind the two together and you get a form that is both well absorbed and doing a second job on the way through. Malic acid is the same idea pointed at energy production rather than sleep.

All three are chelates, which is worth being precise about because it gets challenged. A chelate is a complex in which the carrier binds the metal ion at two or more points, forming a ring. Citric acid has three carboxyl groups and a hydroxyl and binds magnesium at multiple points. Malic acid does the same. Only the Albion form is an amino acid chelate, which is a narrower category, and we do not describe all three that way.

The commercially obvious move is a single form. It is cheaper to buy, simpler to print on a label, and far easier to market, because you get to name one thing and own it. We went the other way, and the reasoning belongs to our co-founder Andrew rather than to me.

Magnesium oxide. On the absorption evidence above, we would have been printing a number we were not proud of.

Capsules and tablets. Four hundred milligrams of elemental magnesium does not fit in one capsule. Matching it means roughly six capsules every night, which is a habit most people abandon by week three. Before Biosphere, the clinic used a different flavoured magnesium product. Making it a drink you look forward to in the evening was half the original idea.

Artificial sweeteners, flavours and colours. Sucralose is considerably cheaper than monk fruit and stevia. We use monk fruit and stevia, with colour from food sources rather than synthetic dyes, because the brief was a product we wanted to take ourselves every day without thinking about it.

A large amount of the raw material we were offered. We rejected a lot of certificates of analysis on magnesium out of China that showed heavy metal levels more than a hundred times higher than the US equivalent. That is a comment on the specific batches we tested and turned down, not a blanket statement: some Chinese material was perfectly good, and the citrate we saw from there was fine. The glycinate we sourced from the United States was simply much cleaner, so that is where it comes from.

The RDA for magnesium is 310 to 420mg a day for adults, varying by age and sex. It is a perfectly good number for what it was built to do, which is stop most of the population developing a deficiency. It was never designed as a target, and it does not move when the person does. A 55kg woman and a 105kg man get the same recommendation.

The balance research points somewhere else. In 1964 Mildred Seelig pulled together the published magnesium balance studies and analysed what intake was actually required to hold a positive balance. Three figures came out of it, and they are still the clearest ones available.

Below roughly 6mg per kilo per day, negative magnesium balance is likely to develop. Above 10mg per kilo, strong positive balances develop, which appear to reflect repletion of suboptimal tissue stores. Her suggested optimal daily intake was 7 to 10mg per kilo. She also noted that the typical Western diet at the time supplied 250 to 300mg a day, under 5mg per kilo for most adults.

Read your own weight off the bottom and you get your range. At 60kg it is 420 to 600mg a day. At 75kg, 525 to 750mg. At 90kg, 630 to 900mg. Sit at the lower end if you are healthy with nothing in particular going on, and toward the higher end if you are training hard, sweating a lot, under sustained stress, or dealing with symptoms.

Two things follow from this that are worth saying out loud. One scoop of a 400mg product is a full functional dose for a smaller adult and a substantial top-up on food for a larger one, not a complete replacement for what you eat. And a 100mg tablet is not a small dose of the right thing. It is a rounding error against the number in the chart. If you want to go deeper on this, we have a longer piece on working out how much magnesium to take.

This is the mental model that makes the rest of it make sense, and it is why people who take magnesium irregularly usually conclude it does nothing.

Paracetamol works on a dose. You take it, the concentration rises, something happens, it falls again. Magnesium does not behave like that. It is a structural mineral, and what matters is the level held in your tissues over weeks. A single large amount does not produce a large effect. It mostly produces a trip to the bathroom.

Which means consistency beats size. Taking 400mg every day for a month does considerably more than taking 800mg twice a week. It also means a supplement that is unpleasant, expensive per serve, or a handful of capsules is quietly failing at the thing that actually matters, because you will stop taking it.

Why a blood test usually will not tell you

People often ask whether they should get their magnesium tested first. It is a fair question and the answer is unsatisfying.

More than 99 per cent of the magnesium in your body sits inside cells and bone, not in serum. Your body defends serum magnesium tightly, drawing on tissue stores to hold it steady, which means serum can read perfectly normal while stores are being run down. A 2018 review in Open Heart makes the point directly: because serum does not reflect intracellular magnesium, most cases of deficiency go undiagnosed.

So in practice you work backwards from intake and demand rather than forwards from a number. What are you eating, how much are you sweating, how much stress are you carrying, are you on medication that depletes magnesium. Our piece on the signs of magnesium deficiency goes through what that looks like. If you want it investigated properly, that is a conversation with your doctor, not with a supplement company.

Sleep is the most commented-on benefit in our reviews, and it is worth understanding the mechanism, because it explains both what to expect and when.

Sleep is by a wide margin the most commented-on benefit in our reviews, across the most reviewed magnesium product in New Zealand. It genuinely helps a lot of people. It is also not a sleeping pill, and anyone selling it to you as one is setting you up to be disappointed.

Andrew again, on the thing we will not say.

The published evidence lines up with that caution more closely than the category's marketing does, and it is worth walking through properly rather than picking the flattering half.

There is a magnesium-specific meta-analysis, and it found something real. Pooling three randomised trials in 151 older adults with insomnia, people taking magnesium fell asleep about 17 minutes faster than those on placebo, with a confidence interval running from 7 to 27 minutes. That is the number you will see quoted, including on our own sleep guide.

Here is the rest of that paper. Total sleep time improved by 16 minutes and did not reach statistical significance. All three trials were judged at moderate-to-high risk of bias. The authors graded the evidence low to very low, which is worth knowing before anyone quotes the seventeen minutes at you as settled.

The wider picture is thinner still. A 2021 review of 31 randomised trials of supplements for sleep quality found significant improvements for amino acids, vitamin D and melatonin. Magnesium had inadequate data to be pooled at all, and the authors called for further research. That is not a negative finding. It is an absence of one, which is a different and more honest thing.

What does exist is observational. The CARDIA study followed nearly 4,000 adults and found that those in the highest quartile of magnesium intake were less likely to be short sleepers, at an odds ratio of 0.64 with a confidence interval of 0.51 to 0.81. Sleep quality itself was borderline and did not reach significance. Observational data cannot establish cause, and the authors say so themselves, calling for randomised trials with objective sleep measures.

Our reading of all that, and it is a reading rather than a fact: correcting a low magnesium level is a different question from treating insomnia. The first is well grounded. The second is a bigger claim than the magnesium evidence supports on its own. If sleep is the whole reason you are here, start with our piece on the best form of magnesium for sleep, which sets out what to expect.

Timing matters less than people hope, with one exception.

If you are taking magnesium primarily for sleep and relaxation, take it in the evening, an hour or so before bed. Not because it stops working at other times, but because the calming end of the effect is more useful then, and because an evening drink is an easier habit to keep than a morning one. If your reason is muscle function, cramps or energy, the time of day is largely irrelevant. Take it when you will remember.

Food is not required. A powder mixed in water absorbs fine on an empty stomach, and if you find any magnesium unsettling at first, taking it with food usually sorts that out.

On expectations: give it two to four weeks before you decide. Some people notice something in the first week, usually in how easily they get to sleep or how their legs feel. Others notice nothing for a fortnight and then realise in retrospect that they have stopped waking at three in the morning. And some people, as above, will not notice anything, because they were not low to begin with.

Food first is not a throwaway line here. It is genuinely the better route if you can get there.

The richest everyday sources are pumpkin seeds, almonds, cashews, spinach and silverbeet, black beans and other legumes, wholegrains, and dark chocolate at a high cocoa percentage. Chlorophyll has magnesium at the centre of the molecule, which is why dark leafy greens keep appearing on these lists.

The catch is arithmetic. A generous handful of pumpkin seeds, which is a lot of pumpkin seeds, gets you somewhere near 150mg. Seelig's own note was that the Western diet supplied 250 to 300mg a day, and the food supply has not obviously improved since. Add in the things that increase your requirement, heavy sweating, sustained stress, high alcohol intake, certain medications, and the gap between what you eat and what the chart above says you need widens rather than closes.

Which is the argument for a supplement, and also the limit of it. A supplement closes a gap. It does not replace a diet. Our full list of foods high in magnesium has the numbers per serve if you want to work out where you already sit.

Three situations where the general advice does not apply cleanly.

Children. The directions on our label are one scoop daily from 14 years, and half a scoop daily from 8 to 13. Below 8, this is not the right product and the amount should come from a GP or a paediatric dietitian rather than from a tub sized for adults. The label also states the product is suitable for diabetics.

Pregnancy. Magnesium requirements do rise in pregnancy, and Biosphere Magnesium is suitable for use during pregnancy. That is on the label rather than an inference, and it is one of the few things on a supplement tub that is genuinely useful to know at a glance. Requirements also vary, so talk to your midwife or doctor about the right amount for you rather than assuming the standard scoop is it. We go through the considerations in our article on taking magnesium supplements during pregnancy.

Medication. Magnesium can interact with several common medicines, and the direction of the interaction varies: some medications deplete magnesium, and magnesium can reduce the absorption of others if taken at the same time. If you are on prescribed medication, particularly for blood pressure, or antibiotics, or thyroid medicine, check with your GP or pharmacist and ask specifically about timing rather than just about whether you can take it.

Anyone with kidney disease should not take magnesium supplements without medical supervision. Impaired kidneys cannot clear excess magnesium efficiently, and that is the one situation where the usual "your gut will tell you" ceiling does not apply.