Quick answer
- Compare elemental magnesium per daily dose, not the weight of the compound: 1,000 mg of magnesium bisglycinate gives roughly 140 mg of magnesium.
- The NHS says 400 mg or less a day from supplements is unlikely to cause harm; EFSA's safe upper level is stricter at 250 mg a day. Above these amounts, diarrhoea becomes more likely.
- Citrate and bisglycinate are the usual choices. Oxide packs the most magnesium per tablet but dissolves poorly.
- Authorised claims (UK and EU) cover tiredness, muscle and nerve function. There is no authorised claim for sleep.
Key numbers
- UK daily need (NHS)
- 300 mg men, 270 mg women
- Adults 19–64, mostly from food.
- UK figure for supplements (NHS)
- 400 mg/day or less
- Unlikely to cause harm; more can cause diarrhoea.
- Reference intake on labels (NRV)
- 375 mg/day
- Total from food and supplements.
- Safe upper level from supplements (EFSA)
- 250 mg/day
- Adults. Food magnesium is not counted.
- Germany (BfR guidance)
- 250 mg/day
- Split into at least two doses.
- Spain
- No national maximum
- Minimum for an authorised claim
- 56 mg per daily dose
- 15% of the NRV.
What these terms mean: NRV upper levels (NHS, EFSA) maximum levels by country daily dose
How to choose
- Find the elemental magnesium per daily dose in the nutrition table, not the "1,500 mg magnesium citrate" on the front of the pack.
- Aim for 100–250 mg of magnesium a day from supplements, within both the EFSA (250 mg) and NHS (400 mg) figures. More is not better and makes loose stools more likely.
- Pick the form: citrate for value, bisglycinate if your stomach is sensitive, oxide only if the lowest price per tablet is all that counts.
- Check for added vitamin B6, common in magnesium products. The NHS says not to take more than 10 mg of B6 a day from supplements.
- Compare the cost per 100 mg of elemental magnesium, not per capsule or per pack.
Magnesium forms compared
The share of elemental magnesium differs a lot between compounds, so two products with the same “1,000 mg” on the front can deliver very different doses.
| Form | Elemental magnesium (approx.) | Compound needed for 200 mg magnesium | Usually chosen for |
|---|---|---|---|
| Oxide | ~60% | ~330 mg | Lowest price per tablet |
| Carbonate | ~28% | ~710 mg | Cheap, often in effervescent tablets |
| Citrate | ~16% | ~1,250 mg | Good absorption at a mid price |
| Malate | ~15% | ~1,330 mg | Alternative to citrate |
| Bisglycinate | ~14% | ~1,430 mg | Gentle on the stomach |
| Chloride (hexahydrate) | ~12% | ~1,670 mg | Powders and liquids |
| L-threonate | ~7% | ~2,860 mg | Marketed for memory; little evidence |
Our magnesium forms guide explains each form in detail.
Maximum magnesium per day, by country
EFSA’s level of 250 mg a day counts magnesium from supplements only and is set to avoid diarrhoea rather than serious harm. National limits range from 250 mg (Germany, Ireland) to 450 mg (Belgium, Italy); the NHS figure is 400 mg.
Limits are per recommended daily dose of a supplement, for adults; several countries set lower ones for children and teenagers. Inside the EU, a product lawfully sold in one country can usually be sold in another even above its limit (mutual recognition). All 7 nutrients and 13 countries →
What the evidence says
Magnesium supplements make the most difference when your diet is low in it: wholegrains, nuts, seeds, legumes and green vegetables are the main food sources. According to the US National Institutes of Health, forms that dissolve well in liquid, such as citrate, chloride and lactate, are absorbed better than oxide.
For sleep, a meta-analysis in older adults found people fell asleep about 17 minutes sooner, on low-quality evidence; see magnesium for sleep. For muscle cramps in older adults, a 2020 Cochrane review concluded that magnesium is unlikely to provide meaningful protection. Neither use has an authorised claim (UK and EU).
What the label may legally claim
Authorised claims (GB and EU registers)
- Contributes to a reduction of tiredness and fatigue
- Contributes to normal muscle function and normal functioning of the nervous system
- Contributes to normal psychological function and normal energy-yielding metabolism
- Contributes to electrolyte balance and the maintenance of normal bones and teeth (all from 56 mg per daily dose)
Not authorised in GB or the EU
- Better or deeper sleep
- Less anxiety or stress
- Preventing muscle cramps
- Preventing migraine
How health claims work (UK & EU): health claims
Products we have checked
Label data checked by NutriMetrics for products sold in Spain and Germany. UK product checks are next. Sorted alphabetically, not ranked.
| Product | Per daily dose | Sold in | Label |
|---|---|---|---|
| Ana María Lajusticia Bisglicinato de magnesioSee label | Not on the label · bisglycinate | Spain | Source |
| Ana María Lajusticia Colágeno con magnesio (comprimidos)6 tablets a day | 185 mg | Spain | Source |
| natural elements Magnesium Bisglycinat3 capsules a day | 300 mg · bisglycinate | Germany | Source |
Who should be careful
- Kidney disease: do not take magnesium supplements without medical advice, because the kidneys clear the excess.
- Medicines: magnesium can reduce the absorption of some antibiotics (tetracyclines, quinolones) and of bisphosphonates for osteoporosis. Take them a few hours apart and ask your pharmacist or GP.
- Loose stools: the most common side effect above about 250 mg from supplements. Split the dose or lower it.
FAQ
Which form of magnesium is best?
There is no single best form. Forms that dissolve well, such as citrate, are absorbed better than oxide; bisglycinate is usually gentle on the stomach but has little head-to-head data. For most people the dose of elemental magnesium and the price per 100 mg matter more than the form.
How much magnesium should I take a day?
The NHS says 400 mg or less a day from supplements is unlikely to cause harm; EFSA considers up to 250 mg a day from supplements safe, on top of what you eat. Most people get what they need (300 mg for men, 270 mg for women, according to the NHS) from food.
Does magnesium help you sleep?
UK and EU law do not allow that claim. In trials, older adults fell asleep about 17 minutes sooner, but the evidence is of low quality and the benefit seems larger in people who eat little magnesium.
Does magnesium prevent cramps?
For older adults with ordinary muscle cramps, a Cochrane review found magnesium unlikely to make a meaningful difference. Cramps in pregnancy were less clear.
Sources
- NHS — Others (magnesium, selenium, zinc)
- NHS — B vitamins and folic acid
- DHSC — Great Britain nutrition and health claims (NHC) register
- European Commission — EU Register of nutrition and health claims
- Commission Regulation (EU) No 432/2012 — list of permitted health claims
- EFSA — Summary of tolerable upper intake levels (2024)
- BfR — Recommended maximum daily amount of magnesium in food supplements
- NIH Office of Dietary Supplements — Magnesium fact sheet for health professionals
- Garrison SR et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev, 2020
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: systematic review and meta-analysis. BMC Complement Med Ther, 2021
Information only, not medical advice. No product on this page is a paid placement.