What Is Magnesium Good For? The Vitamins and Minerals Guide

Magnesium is good for the things your muscles, nerves and energy metabolism do every minute: it contributes to normal muscle function, normal functioning of the nervous system, normal energy-yielding metabolism, normal psychological function, the maintenance of normal bones and teeth, normal protein synthesis, electrolyte balance and a reduction of tiredness and fatigue.¹ Those are its authorised UK roles; the longer lists online, from heart rhythm to sleep, are unproven or medical. The UK reference intake is 300 mg a day for men and 270 mg for women, most adults get less, and the figure that matters on a supplement is the elemental magnesium, not the compound weight.² This page is the hub for our vitamins and minerals guides. It covers magnesium in full and carries the two tables every other page points to: supplement forms by elemental dose, and the UK units that cause most of the confusion.

• Magnesium does: muscle and nerve function, energy release, psychological function, bones and teeth, tiredness and fatigue
• Intake: 300 mg men, 270 mg women; labels use 375 mg; supplements up to 400 mg a day
• Forms: glycinate, citrate, oxide, malate and others differ in elemental content and in what the small absorption studies measured, not in what the magnesium does
• Who runs short: low-wholegrain diets, heavy drinkers, gut conditions, long-term acid suppressants and diuretics, type 2 diabetes, older age
• Not authorised: sleep, anxiety, blood pressure, palpitations, migraine; the pages below say what the evidence shows

What magnesium does in the body

Magnesium is a cofactor for more than 300 enzymes. It stabilises the molecule that carries energy inside cells, hence the authorised wording on energy metabolism and tiredness; it balances calcium across nerve and muscle membranes, letting muscles relax and nerves fire at the right threshold, hence cramps, twitching and tingling when it runs short; and more than half of the body's store is in bone.^{2, 3} Blood carries less than 1% of the total, so a blood test under-reads mild shortfall, and the kidneys control the balance, keeping what is needed and excreting the rest. That is why food magnesium has no upper limit, why supplements have a laxative threshold rather than a toxic one, and why kidney disease is the one condition in which it accumulates dangerously.

How much magnesium do you need?

300 mg a day for men and 270 mg for women aged 19 to 64, the UK reference nutrient intake, lower than the American figures quoted online. The 375 mg on labels is the European reference value used for percentages, not a target. National diet surveys find a minority of adults, and around half of teenage girls, below the lower reference intake, almost always because wholegrains, nuts, seeds, pulses and green vegetables are missing from the plate.² Which foods contain magnesium lists UK portions in milligrams and shows how to reach 300 mg from food. How much magnesium per day, by age and sex, gives the amounts for children, pregnancy and older adults.

Which magnesium supplement, and what the label means

Every magnesium supplement is magnesium bound to something else, and the label's headline number is often the weight of the whole compound. "Magnesium glycinate 1,000 mg" contains roughly 100 to 140 mg of magnesium; a label reading "magnesium 200 mg (as bisglycinate)" is giving you the elemental figure. The UK guidance for supplements is to stay at or below 400 mg of elemental magnesium a day, above which loose stools become likely.⁴ Approximate elemental content:

• Magnesium oxide: about 60% magnesium by weight, so the smallest tablet for a given dose; absorbed less than citrate or chloride in the urine-based studies (4% in one), more than citrate on a cell measure in another; the salt used in several of the sleep, cramp and mood trials^{5, 6}
• Magnesium citrate: about 8 to 16%, depending on the salt and its water; dissolves readily and raised blood and urinary magnesium more than oxide in most comparison studies; a citrate-and-picosulfate medicine, at a medicine dose, is used to clear the bowel before procedures⁷
• Magnesium glycinate or bisglycinate: about 10 to 14%; reported as better tolerated than oxide in a 12-person study and no more likely than placebo to upset the stomach at 300 mg a day in 80 pregnant women; one supplier-funded single-dose crossover in 40 healthy adults compared it with citrate and oxide on bowel effects, too short to rank them^{8, 9, 10}
• Magnesium malate: about 15%; one 24-person trial and no human absorption study of its own
• Magnesium taurate, threonate and others: 7 to 10%; the fewest human studies of the common salts
• Sprays, oils and bath flakes: magnesium chloride or sulphate on the skin; absorption through skin is unproven and small

Small absorption studies mostly favour citrate and the chelates over oxide on urine and blood measures, though the supplier-funded single dose found no significant plasma rise after bisglycinate and no difference between salts over six hours; one favoured oxide inside cells, and the 2017 review found dose and existing level matter more than the salt.^{10, 11} The directory of every permitted form, types of magnesium, lists the rest, and how to read a magnesium label works the arithmetic. Which magnesium is best compares the four common salts by what the studies measured, and what is magnesium glycinate covers the most searched one. Is it OK to take magnesium every day covers dose, who should not, and the medicines that need spacing.

Who runs short, and the signs

Low intake from a refined diet; heavy alcohol use; chronic diarrhoea, coeliac or Crohn's disease; long-term proton pump inhibitors such as omeprazole; loop and thiazide diuretics; poorly controlled type 2 diabetes; and older age, which brings several together.³ The signs, in order: tiredness and weakness, muscle cramps and twitching, numbness and tingling, nausea and poor appetite, low mood, and, when marked, palpitations. The signs of low magnesium goes through the seven signs, the myths and when to see a GP.

Sleep, anxiety, blood pressure, palpitations, migraine: what the evidence shows

None of these is an authorised claim for magnesium, so no UK supplement may say it helps them, and this hub does not either. For sleep: a handful of small trials in older adults with low intakes, a modest effect on falling asleep, and one supplier-funded 21-day threonate trial in 80 adults not screened for status;¹² does magnesium help you sleep has the detail. For anxiety and low mood: associations with low status, mixed and weak supplement trials.¹³ For palpitations and heart rhythm: a medical question, because magnesium is sometimes prescribed for rhythm problems and sometimes unsuitable; new palpitations need a GP, and anyone with a rhythm condition should ask their cardiologist before taking it. For migraine: some trials (the 81-person trial used 600 mg a day as citrate for 12 weeks, with diarrhoea in one in five), no UK claim, a neurologist question.¹⁴

Blood pressure has the most trials and no authorised wording. Across 34 placebo-controlled trials of 2,028 adults, about 370 mg a day for three months lowered systolic pressure by 2.00 mmHg and diastolic by 1.78 on average.¹⁵ In 11 trials of 543 people with insulin resistance, prediabetes or a related chronic condition, the falls were 4.18 and 2.27 mmHg.¹⁶ A 2021 review sorted 49 trials by who was studied: falls at ordinary doses appeared only in people whose blood-pressure tablets had not fully controlled their pressure, people with normal or controlled pressure showed no change at any dose, and its authors declare industry honoraria.¹⁷ No claim is authorised for magnesium on blood pressure, the averages are small, and no trial tested it in place of a medicine. If you take blood-pressure tablets, tell your GP that you take magnesium, and what you should not take with magnesium covers the medicines.

The UK units, in one place

• Vitamin D: 1 microgram = 40 IU. 10 micrograms = 400 IU (the UK daily advice); 25 micrograms = 1,000 IU; 100 micrograms = 4,000 IU (the adult upper limit). Blood levels in nmol/L: below 25 deficient, above 50 sufficient; 1 ng/mL = 2.5 nmol/L.
• Vitamin B12: the reference intake is 1.5 micrograms, not milligrams. Supplements of 10 to 1,000 micrograms are safe. UK blood tests use ng/L or pmol/L; NICE 2024 sets an indeterminate band that needs a second test.
• Folic acid: 400 micrograms (0.4 mg) is the pregnancy dose; 5 mg is 5,000 micrograms and prescription-only; 1 mg is the guidance ceiling otherwise.
• Iron: labels state the compound; 200 mg ferrous sulphate is 65 mg iron, 210 mg ferrous fumarate is 69 mg, a liquid sachet is often 5 to 14 mg. Ferritin below 30 micrograms per litre is iron deficiency in UK guidance.
• Magnesium: elemental figure as above; 400 mg a day is the supplement guidance level.
• Vitamin B6: 10 mg a day is the UK long-term supplement guidance; nerve damage is reported above about 50 mg over months.

Magnesium guides

• How to choose a magnesium supplement: reading the label, which is elemental magnesium per dose, the salt and the NRV percentage.
• Types of magnesium: every UK-permitted form, with the elemental dose of each and what its studies measured.
• How much magnesium per day: the UK amounts by age and sex, children included.
• When is the best time to take magnesium: morning or night, with or without food.
• Magnesium side effects: diarrhoea, nausea and headaches, dose by dose.
• What is magnesium citrate: elemental dose, the absorption studies, where it is a medicine.
• Magnesium sprays, oils, flakes and Epsom baths: the skin studies.
• Which magnesium is best: the four common salts by what the studies measured, and the sleep-form question.
• What is magnesium glycinate: the form, the bisglycinate name and "buffered" blends.
• Is it OK to take magnesium every day: the 400 mg and 250 mg figures, signs of too much, who asks first.
• What you should not take with magnesium: the medicines to separate and the ones to ask about.
• The signs of low magnesium: the seven signs, the causes and the blood test.
• Does magnesium help you sleep: the older-adult trials.
• Which foods contain magnesium: UK portions in milligrams.
• Can you take zinc and magnesium together: doses and spacing.

When should you take magnesium? No trial we found has compared times of day; when is the best time to take magnesium has the detail.

Every guide in this series

Magnesium: see the guides above. Vitamin D: the vitamin D guide, foods highest in vitamin D, what vitamin D3 is good for, vitamin D2, vitamin D for vegans, what not to take with vitamin D, mushrooms and vitamin D, when to take vitamin D, babies and children, pregnancy and breastfeeding, checking your levels and sun in the UK. Silica: what is silica good for. B vitamins: what B complex is for, B complex every day, when to take B complex, B12 or B complex, what B12 is good for, B12 for women, thiamine, biotin and hair. Folate and iron: folic acid for women, folic acid in pregnancy, iron and heavy periods. Vitamin A: what vitamin A is good for. Vitamin C and zinc: what vitamin C is good for, what is zinc good for, vitamin C and zinc together. Immune system: vitamins for the immune system. Formats: do vitamin gummies work. New guides: signs of vitamin D deficiency, too much vitamin D, vitamin D3 and K2, signs of B12 deficiency, foods high in B12, folate deficiency symptoms, foods high in folate, foods high in iron, iron supplement side effects, signs of zinc deficiency, foods high in zinc, foods high in calcium, how to choose a multivitamin for women, which menopause supplements have evidence and what is the menopause.

If you want a magnesium supplement

Food brings fibre and potassium with it. If your diet cannot carry enough, or you take a proton pump inhibitor or diuretic, or you have the signs above and a GP has found nothing else, a plain form at 100 to 300 mg of elemental magnesium a day, within the 400 mg guidance, is sensible. Magnesium contributes to normal muscle function, normal functioning of the nervous system, normal psychological function, normal energy-yielding metabolism, the maintenance of normal bones and a reduction of tiredness and fatigue. Anyone with kidney disease should not take magnesium without medical advice.

What we don't know

• How common mild magnesium shortfall is. Blood tests miss it and intake surveys over-simplify it.
• How large the absorption advantage of the organic forms is over oxide at matched elemental dose. The studies are small.¹⁰
• Whether magnesium helps sleep, mood or migraine in people with normal status. No authorised claim; trials mixed.¹³

Frequently asked questions

What is magnesium good for?

Normal muscle and nerve function, releasing energy from food, normal psychological function, normal bones and teeth, protein synthesis, electrolyte balance and reducing tiredness and fatigue, which are its authorised UK roles.¹

Can too much magnesium hurt your kidneys?

Healthy kidneys excrete excess magnesium; the problem runs the other way, in that kidney disease lets magnesium accumulate. People with kidney disease should not take magnesium supplements without medical advice.

Should I take a magnesium supplement?

The NHS says you should be able to "get all the magnesium you need by eating a varied and balanced diet" and that "400mg or less a day of magnesium from supplements is unlikely to cause any harm" (page reviewed 3 August 2020).¹ A supplement is the usual way to close a gap when intake sits below the 300 mg or 270 mg reference intake, or when a long-term proton pump inhibitor or a diuretic lowers your level; magnesium contributes to normal muscle function and a reduction of tiredness and fatigue.^{2, 3} With kidney disease, ask your GP first.

Does magnesium help with weight loss?

Across 32 trials, magnesium did not change body weight, waist or body fat; a borderline 0.2-point BMI difference appeared only in people who were deficient or insulin-resistant at the start.¹⁸ The authorised wording that magnesium contributes to normal energy-yielding metabolism is not a weight claim.

Is manganese the same as magnesium?

No: they are different elements with different jobs. The NHS minerals page lists both and gives a daily amount only for magnesium: magnesium helps turn food into energy, manganese helps make and activate some enzymes.¹

Sources

1. NHS. Vitamins and minerals: others, including magnesium. nhs.uk; Great Britain nutrition and health claims register.
2. Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutrition Reviews, 2012. PubMed 22364157.
3. Liamis G, et al. An overview of diagnosis and management of drug-induced hypomagnesemia. Pharmacology Research and Perspectives, 2021. PubMed 34278747.
4. Costello R, et al. Perspective: call for re-evaluation of the tolerable upper intake level for magnesium supplementation in adults. Advances in Nutrition, 2023. PubMed 37487817.
5. Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnesium Research, 2001. PubMed 11794633.
6. Shechter M, et al. Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects. Magnesium Research, 2012. PubMed 22433473.
7. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research, 2003. PubMed 14596323.
8. Schuette SA, Lashner BA, Janghorbani M. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN Journal of Parenteral and Enteral Nutrition, 1994. PubMed 7815675.
9. Supakatisant C, Phupong V. Oral magnesium for relief in pregnancy-induced leg cramps: a randomised controlled trial. Maternal and Child Nutrition, 2015. PubMed 22909270.
10. Pajuelo D, et al. Comparative clinical study on magnesium absorption and side effects after oral intake of microencapsulated magnesium and other forms. Nutrients, 2024. PubMed 39770988. Supplier-funded single-dose crossover, 40 adults.
11. Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium: an update. Current Nutrition and Food Science, 2017. PubMed 29123461.
12. Hausenblas HA, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Medicine: X, 2024. PubMed 39252819. Supplier-funded randomised trial, 80 adults, 21 days.
13. Boyle NB, Lawton C, Dye L. The effects of magnesium supplementation on subjective anxiety and stress: a systematic review. Nutrients, 2017. PubMed 28445426.
14. Peikert A, Wilimzig C, Köhne-Volland R. Prophylaxis of migraine with oral magnesium: results from a prospective, multi-center, placebo-controlled and double-blind randomized study. Cephalalgia, 1996. PubMed 8792038.
15. Zhang X, et al. Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension, 2016. PubMed 27402922.
16. Dibaba DT, et al. The effect of magnesium supplementation on blood pressure in individuals with insulin resistance, prediabetes, or noncommunicable chronic diseases: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition, 2017. PubMed 28724644.
17. Rosanoff A, Costello RB, Johnson GH. Effectively prescribing oral magnesium therapy for hypertension: a categorized systematic review of 49 clinical trials. Nutrients, 2021. PubMed 33435187.
18. Askari M, et al. The effects of magnesium supplementation on obesity measures in adults: a systematic review and dose-response meta-analysis of randomized controlled trials. Critical Reviews in Food Science and Nutrition, 2021. PubMed 32654500.

This article is general information, not medical advice. Palpitations, persistent cramps or tingling need a GP; people with kidney disease or a heart rhythm condition should ask their doctor before taking magnesium.