There are eight jars of magnesium on the shelf and none of them explains the difference. Bisglycinate, citrate, threonate, carbonate, oxide. Prices run from eight to fifty-five euros and every label promises the same three things: energy, rest, muscle.
The difference is real, but it isn't where the advertising puts it. The question isn't which is the best magnesium — it's what you absorb, what agrees with you, and what you want it for. And there is one use, the biggest seller of all, for which the evidence is fairly clear that it doesn't work.
The short version
- EFSA sets the adequate intake at 350 mg a day for men and 300 mg for women.
- What counts isn't what the capsule weighs, it's the elemental magnesium and what your gut absorbs. Oxide and sulfate are poorly absorbed; citrate, lactate, chloride and aspartate considerably better.
- Bisglycinate: the gentlest on the stomach. The default choice for daily use.
- Citrate: good absorption plus a mild laxative effect. Useful if you're also constipated, annoying if you're not.
- L-threonate: the expensive one, the one that promises to reach the brain. Human evidence is still thin.
- For night cramps, a Cochrane review of 11 trials concludes it offers no clinically meaningful benefit in older adults. It's the most popular use and the worst supported.
- The upper limit for supplemental magnesium is 350 mg a day. Magnesium from food doesn't count towards it.
What magnesium actually does, and why many people fall short
Magnesium acts as a cofactor in more than three hundred enzymatic reactions. European regulation allows us to say, with backing, that it contributes to the normal functioning of the nervous system and the muscles, to normal protein synthesis, to electrolyte balance, to normal psychological function, to the maintenance of bones and teeth, and to the reduction of tiredness and fatigue. It's a long list precisely because magnesium doesn't do one thing: it's involved in almost everything.
The problem is intake. The NHANES 2013-2016 analysis found that 48% of Americans consume less magnesium than recommended for their age and sex. That's US data, not Spanish, and it's worth saying so. But the mechanism behind it looks familiar: magnesium lives in whole grain, pulses, seeds, nuts and leafy greens, and refining cereal strips out much of what was there. A diet built on white bread, with few pulses and little veg, falls short without anyone noticing, because a mild shortfall doesn't hurt — it tires.
The forms of magnesium, one by one
1. Bisglycinate: the best tolerated
Magnesium bound to two glycine molecules. Its documented advantage is digestive tolerance: because it's absorbed by a different route from inorganic salts, it draws less water into the gut and causes less diarrhoea. That makes it the sensible form if you're taking it every day at a moderate dose.
One honest caveat: the NIH magnesium fact sheet, which does compare aspartate, citrate, lactate and chloride against oxide and sulfate, doesn't even list glycinate among the forms with published bioavailability data. Its reputation as "the best absorbed" runs ahead of the head-to-head comparisons. What is clear is that it sits better. You'll find Sura Vitasan's bisglycinate in our nervous system section.
2. Citrate: good absorption, with a built-in side effect
One of the best studied and best absorbed forms. It has a mild osmotic laxative effect that may be exactly what you want or exactly what you don't. If you have a sluggish gut, it's two benefits for one; if your gut is sensitive, start at half the dose. It comes alone or blended, as in Be Levels' Triple Magnesium, which mixes several salts to spread absorption and tolerance. If your underlying issue is digestive, look at digestive system and enzymes and probiotics too.
3. L-threonate: the expensive one, and still the least proven
Magnesium L-threonate was patented on the hypothesis that it crosses the blood-brain barrier better and raises brain magnesium. The hypothesis is interesting and the bulk of the data supporting it comes from animal studies. Human trials are few, small and short. It isn't snake oil, but it isn't what the marketing suggests either: today it's a reasonable bet if you have budget to spare, not an obvious purchase. Kal's Magnesium L-Threonate sits in the same nervous system section.
4. Oxide and carbonate: a lot of paper, not much prize
They carry plenty of elemental magnesium per capsule and absorb poorly. Oxide is the standard filler in cheap multivitamins. Magnesium carbonate has its own legitimate use as an antacid, and there it does the job. As a source for correcting a low intake, it isn't the first choice.
5. Chloride and lactate: the quiet ones that work
Soluble, well absorbed, without the reputation of the others and at half the price. Chloride is also used topically, though transdermal absorption is far less well documented than the claims suggest.
6. Combined formulas: when they make sense
A "triple magnesium" splits the dose across salts with different profiles, which usually improves tolerance. Combinations with vitamin D and K2 make sense for bone health, because magnesium is involved in activating vitamin D. If that's your goal, look at bones and joints and vitamins and minerals. Webotanix's triple formula follows the same logic.
Comparison table: what to expect from each form
| Form | Absorption | Digestive effect | Who it suits | Price |
|---|---|---|---|---|
| Bisglycinate | Good | Very gentle | Daily use, sensitive gut | Mid-high |
| Citrate | Good, well documented | Mildly laxative | Sluggish transit | Mid |
| L-threonate | Good | Gentle | Cognitive goal, with budget | High |
| Chloride / lactate | Good | Moderate | Value for money | Low-mid |
| Carbonate | Low | Antacid | Occasional acidity | Low |
| Oxide | Low | Strongly laxative | Poor choice as a source | Very low |
Practical table: what you want and what suits you
| What you want | Sensible form | When to take it | Note |
|---|---|---|---|
| Sleep better | Bisglycinate | Dinner or before bed | The effect, if any, is modest |
| Tiredness and stress | Bisglycinate or citrate | Morning or split | Check sleep and caffeine first |
| Sluggish transit | Citrate | Night | Start at half a dose |
| Bone health | Combined with D3 and K2 | With a meal containing fat | Vitamin D needs magnesium |
| Hard training | Citrate or chloride | After training | Look at sodium and potassium too |
| Night cramps | None, on the evidence | — | See the next section |
The cramp myth: what the Cochrane review says
It's the reason most people buy magnesium and the worst supported of all. The Cochrane review by Garrison and colleagues pooled 11 trials and 735 participants: five in pregnant women, five in older people with idiopathic cramps and one in people with cirrhosis.
In the older group — the classic night cramp in the calf — differences in cramp frequency were small and not statistically significant. In pregnancy the results were inconsistent: some studies found a benefit, others didn't. The authors conclude that magnesium is unlikely to provide clinically meaningful cramp prophylaxis to older adults.
Saying this costs us sales, but it's what the evidence shows. If you get night cramps, the sensible things to check before supplementing are hydration and salts — we cover that in how to hydrate properly — stretching before bed, and whether any medication you take encourages them.
Where magnesium does have reasonable backing is migraine prevention: the American Academy of Neurology and the American Headache Society consider it probably effective. And for blood pressure the effect is real but small: around a 2.2 mmHg drop in diastolic pressure over 8 to 26 weeks of supplementation.
Where magnesium lives in food
Before the jar, the pantry. These are the real sources, per normal portion:
| Food | Portion | Magnesium |
|---|---|---|
| Pumpkin seeds | 30 g | ~165 mg |
| Chia seeds | 30 g | ~118 mg |
| Almonds | 30 g | ~85 mg |
| Cooked spinach | 90 g | ~78 mg |
| Cashews | 30 g | ~79 mg |
| Banana | 1 medium | ~32 mg |
Two tablespoons of pumpkin seeds and a handful of almonds put you halfway to the daily target without opening a single jar.
The shopping list
If you'd rather raise your magnesium through food, this is what to keep at home:
- Seeds: pumpkin, chia, sesame, sunflower. The densest and cheapest way to move the number.
- Nuts: almond, cashew, Brazil nut.
- Pulses: chickpea, black bean, lentil. Three or four times a week changes the outcome.
- Whole grains: oats, buckwheat, quinoa. Wholemeal, not refined — that's where the difference is.
- Leafy greens: spinach, chard, kale.
- Dark chocolate, 70% and up, in moderation.
- Plant protein for meals built around pulses.
- Superfoods like raw cacao or spirulina, if they suit you.
- Frozen vegetables so you're not dependent on having fresh.
- Drinks with minerals and teas alongside.
- Organic baskets if you'd rather have the veg sorted every week.
- The whole pantry, if you want to browse properly.
Do you actually need a supplement?
Probably not, if you eat pulses three or four times a week, nuts most days, leafy greens and whole grains. That pattern gets you to 300-350 mg without trying.
Supplementing makes more sense if you recognise yourself in one of these: a diet built on refined foods, hard training with heavy sweating, long-term use of proton pump inhibitors or diuretics, high alcohol intake, or a sustained period of stress — we wrote about that in chronic stress and the nervous system.
And a number almost nobody checks: the tolerable upper limit for supplemental magnesium is 350 mg a day. It doesn't include magnesium from food, which has no ceiling because the kidney handles it. Going past it with capsules is the fast route to diarrhoea, nausea and cramping. If you take medication — certain antibiotics and bisphosphonates in particular — magnesium can interfere with absorption: separate them by several hours and check with your doctor.
Frequently asked questions
Which magnesium is best?
There isn't one that's best for everything. For daily use and a sensitive stomach, bisglycinate. If you also have sluggish transit, citrate. For bone health, combined with vitamin D3 and K2. Oxide is the worst absorbed and the most common in cheap products.
Magnesium in the morning or at night?
No hour is demonstrably better. Many people take it at night because they find it relaxing and because citrate, taken during the day, dictates their schedule. Splitting the dose in two improves tolerance and absorption.
Does magnesium help you sleep?
It can help, particularly if you're starting from a low intake, but the documented effect is modest and it doesn't replace consistent hours, light exposure and caffeine control. Our sleep section has melatonin and herbal formulas; plants and extracts has valerian and passionflower.
How much magnesium a day?
EFSA sets the adequate intake at 350 mg a day for men and 300 mg for women, counting food and supplements together. If you supplement, the ceiling on the supplement portion is 350 mg a day.
Does magnesium cause diarrhoea?
Some forms do. Oxide and citrate have an osmotic laxative effect; bisglycinate is the gentlest. If it happens, lower the dose, split it in two or change form before giving up.
Where can I buy organic magnesium in Barcelona and Sant Cugat?
At Linverd Market's three shops: Provença 242 (08008 Barcelona, Eixample), Còrsega 78 (08029 Barcelona, near Sants) and Antoni Bell 2 (08174 Sant Cugat del Vallès, Volpelleres). Also online, across vitamins and minerals and nervous system. If you're torn between two forms, ask in store — that's the advantage of buying somewhere with someone behind the counter.
In short
Start with food: seeds, nuts, pulses and whole grains. If you're going to supplement, choose the form by your tolerance and your goal, not by price or by the front of the jar. And if what you want is your night cramps gone, the evidence says look elsewhere.
Browse the full range in vitamins and minerals, or drop by Provença 242, Còrsega 78 or Antoni Bell 2. Phone: 683 118 961.
If this was useful, carry on here: Should I take creatine every day? and Back to routine: a gut reset after summer.
This information is for general guidance and does not replace advice from a healthcare professional. If you take medication, are pregnant or have kidney disease, check before supplementing with magnesium.