Magnesium: Roles, Food Sources, Deficiency, Evidence, Forms and Safety
Magnesium's roles, food sources, deficiency, official intake figures and upper limits, what trials found for blood pressure, diabetes, migraine and cramps, forms and safety.
Content last updated . This page has not been medically reviewed.
What is Magnesium good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Nerve function
Established roleMagnesium helps nerves work normally.
Supplements: Supplements correct low intake; no good evidence of extra benefit when intake is adequate.
Muscle function
Established roleMagnesium helps muscles contract and relax normally.
Supplements: Supplements correct low levels. A Cochrane review found them unlikely to prevent cramps in older adults.
Steady heartbeat
Established roleMagnesium helps keep the heart beating in a steady rhythm.
Supplements: Supplements are not currently advised by MedlinePlus to prevent heart disease; correct low levels only.
Energy production
Established roleMagnesium helps the body turn food into energy.
Supplements: No good evidence in the sources read that extra magnesium raises energy when intake is adequate.
Strong bones
Established roleMagnesium is part of keeping bones strong.
Supplements: Supplements correct low intake; no good evidence of extra benefit when intake is adequate.
Blood sugar control
Established roleMagnesium helps the body regulate blood sugar.
Supplements: Research is ongoing; MedlinePlus does not currently advise supplements for diabetes.
Immune health
Established roleMedlinePlus lists immune health among magnesium's roles.
Supplements: Supplements correct low intake; no good evidence of extra benefit when intake is adequate.
Protein production
Established roleMagnesium takes part in making protein in the body.
Supplements: Supplements correct low intake; no good evidence of extra benefit when intake is adequate.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (2)
- Bone HealthEstablished role
Magnesium is part of normal bone function. Whether supplements improve bone health beyond correcting low intake was not verified.
- Reduce FatigueDeficiency link
Fatigue is a symptom of true magnesium deficiency, which is uncommon. Supplements are not shown to reduce fatigue in people who are not low.
Body systems (11)
- Bones, Joints & MusclesEstablished role
Magnesium is needed for normal muscle function and strong bones. Low levels can cause muscle spasms, cramps and weakness.
- Kidney & UrinaryDocumented risk
Kidneys clear extra magnesium. When kidney function is greatly reduced, magnesium can build up to harmful levels.
- Musculoskeletal SystemEstablished role
Magnesium is needed for normal muscle function and strong bones. Low levels can cause muscle spasms, cramps and weakness.
- Nervous SystemEstablished role
Magnesium is needed for normal nerve function. Low levels can cause numbness, tingling and seizures.
- Urinary SystemDocumented risk
Kidneys clear extra magnesium. When kidney function is greatly reduced, magnesium can build up to harmful levels.
- Blood Sugar SupportEstablished role
Magnesium helps the body regulate blood sugar. Research is ongoing and supplements are not currently advised for diabetes prevention or control.
- Cardiovascular SystemEstablished role
Magnesium helps keep the heartbeat steady. Moderate deficiency can cause irregular heart rhythms, but supplements are not currently advised to prevent heart disease.
- Digestive SystemDocumented risk
Large amounts of magnesium from supplements or laxatives can cause diarrhoea and cramping. Bowel disease and chronic diarrhoea can also lead to low magnesium.
- Energy & FatigueEstablished role
Magnesium helps turn food into energy, and fatigue is an early sign of true deficiency. This does not show that extra magnesium raises energy when intake is adequate.
- Heart & CirculationEstablished role
Magnesium helps keep the heartbeat steady. Moderate deficiency can cause irregular heart rhythms, but supplements are not currently advised to prevent heart disease.
- Endocrine SystemEstablished role
The NHS says magnesium helps the parathyroid glands work normally; these glands make hormones important for bone health.
Body parts (5)
- KidneysDocumented risk
The kidneys remove extra magnesium. Magnesium products need extra care in people with kidney disease.
- MusclesEstablished role
Magnesium is needed for normal muscle function. Low levels cause cramps, spasms and weakness; a Cochrane review found supplements unlikely to prevent cramps in older adults.
- Nervous SystemEstablished role
Magnesium is needed for normal nerve function. Low levels can cause numbness, abnormal eye movements and convulsions.
- BonesEstablished role
Magnesium is part of keeping bones strong, according to MedlinePlus. Supplement benefit for bone disease was not verified in the sources read.
- HeartEstablished role
Magnesium helps keep the heartbeat steady. Low levels can cause irregular heart rhythms, and severe untreated deficiency can lead to cardiac arrest.
Functional actions (3)
- Energy ProductionEstablished role
Magnesium takes part in turning food into energy. It does not follow that extra magnesium boosts energy in people who are not low.
- Nervous System SupportEstablished role
Magnesium is needed for normal nerve function; supplements help mainly where intake or blood levels are low.
- Endocrine SupportEstablished role
The NHS says magnesium helps the parathyroid glands work normally.
Root causes (4)
- Medication Side EffectsDocumented risk
Some medicines lower magnesium, including diuretics, proton pump inhibitors and certain antibiotics and anti-cancer drugs. Magnesium products can also affect how other medicines are taken.
- Nutrient DeficiencyDeficiency link
Low magnesium can cause fatigue, weakness, cramps, numbness and irregular heart rhythm. True deficiency is uncommon in healthy people.
- AgingDeficiency link
MedlinePlus lists older age as a reason people may have low magnesium.
- Digestive DysfunctionDeficiency link
Malabsorption, celiac disease, inflammatory bowel disease and chronic diarrhoea can lead to low magnesium.
Habits (1)
- Balanced NutritionEstablished role
Magnesium comes from food such as leafy greens, nuts, seeds, beans and whole grains, so a varied diet is the main source.
Biomarkers (1)
- MagnesiumEstablished role
A blood test measures magnesium (normal range about 1.6 to 2.6 mg/dL, varies by lab). A urine test may also be used.
Conditions & symptoms (9)
- HypermagnesemiaDocumented risk
High magnesium is rare from food and mostly happens with greatly reduced kidney function, usually from high-dose supplements or magnesium laxatives.
- HypomagnesemiaDeficiency link
Low blood magnesium can cause convulsions, muscle spasms and weakness, and can be life-threatening if untreated. Treatment is by a clinician.
- Kidney FailureDocumented risk
Reduced kidney function lets magnesium build up, so people with kidney disease should check with a doctor before using magnesium products.
- Magnesium DeficiencyDeficiency link
True deficiency is uncommon. Early signs are poor appetite, nausea, fatigue and weakness; later numbness, cramps, seizures and irregular heartbeat.
- Cardiac ArrhythmiaDeficiency link
Irregular heart rhythm is a sign of moderate magnesium deficiency; untreated severe low magnesium can lead to cardiac arrest.
- DiarrheaDocumented risk
Higher amounts of magnesium taken short term can cause diarrhoea and cramping; magnesium is also used in laxatives.
- HypocalcemiaDeficiency link
Severe magnesium deficiency can come with low blood calcium.
- HypokalemiaDeficiency link
Severe magnesium deficiency can come with low blood potassium.
- Muscle CrampDeficiency link
Cramps are a symptom of low magnesium but have many other causes. A Cochrane review found supplements unlikely to prevent cramps in older adults.
Urgent first
Very low blood magnesium can be a life-threatening emergency. Contact a clinician right away if you have symptoms such as muscle spasms, convulsions or severe weakness. [1] If someone has swallowed too much of a magnesium product, US Poison Help is 1-800-222-1222; call 911 if the person has collapsed, had a seizure, has trouble breathing or cannot be awakened. [2] For other countries see Poison Help by country.Overview
Magnesium is an essential mineral. MedlinePlus says the body needs it for more than 300 biochemical reactions, including normal nerve and muscle function, a steady heartbeat, strong bones and blood glucose control. [3] Research on magnesium for high blood pressure, heart disease and diabetes is ongoing, and MedlinePlus says taking magnesium supplements is not currently advised as a general measure. [3] Evidence labels below: promising but limited, mixed and no meaningful benefit shown.Food sources
Most dietary magnesium comes from dark green leafy vegetables. Other sources named by MedlinePlus are bananas, dried apricots, avocados, almonds, cashews, beans, peas, seeds, soy foods such as tofu, whole grains such as brown rice and millet, and milk. [3] The NHS names spinach, nuts and wholemeal bread. [4]Official intake levels and upper limits
These are published reference values for groups of healthy people, not personal advice. More detail by age and pregnancy is on Magnesium intake levels and the supplement upper limit.| Source, group and year | Value |
|---|---|
| NHS (UK), adults 19-64; page reviewed 2020 | 300 mg a day men, 270 mg women [4] |
| EFSA (EU), Adequate Intake, adults 18 and over; 2017 | 350 mg a day men, 300 mg women [5] |
| US Recommended Dietary Allowance, adults 31 and over (MedlinePlus, 2025) | 420 mg a day men, 320 mg women [3] |
| Daily Value on US labels (a labeling reference, not a requirement) | 420 mg [6] |
| US upper level, supplemental magnesium only, ages over 8 (Institute of Medicine, described by FDA) | 350 mg a day [7] |
| EFSA (EU), upper level for readily dissociable magnesium salts, adults and children from 4 years; 2001 opinion | 250 mg a day, not counting food [8] |
| NHS (UK), from supplements | 400 mg or less a day is unlikely to cause harm [4] |
The upper levels apply only to magnesium from supplements or medicines, not from food. [7]
Who may need assessment
MedlinePlus lists alcohol misuse, bowel disease or surgery that causes malabsorption, older age and type 2 diabetes as reasons people may lack magnesium. [3] Other causes include chronic diarrhea, celiac disease, inflammatory bowel disease and medicines such as diuretics and proton pump inhibitors. [1] Symptoms such as fatigue, weakness, cramps or numbness are not specific to magnesium and cannot diagnose a deficiency. A clinician decides; see Magnesium deficiency: causes, symptoms and who is at risk.Deficiency and excess
- Deficiency. MedlinePlus says it is rare to be truly lacking in magnesium. [3] Treatment depends on severity and may include fluids, magnesium by mouth or vein, and treating the cause. [1]
- Excess. Side effects from food are uncommon except when kidney function is greatly reduced. Excess most often comes from supplements or magnesium-containing laxatives. [3] High blood magnesium is uncommon and most cases happen in people with kidney failure. [9]
- Supplement side effects. FDA lists osmotic diarrhea, nausea and abdominal cramping from sources other than food. [7] See Magnesium side effects, toxicity and kidney disease.
Evidence by use
| Use | What the source found | Label |
|---|---|---|
| Blood pressure | A meta-analysis of 34 placebo-controlled trials (2,028 adults) found a median 368 mg a day for 3 months lowered systolic pressure by 2.00 mm Hg and diastolic by 1.78 mm Hg. [10] FDA said the evidence is inconsistent and inconclusive and it intends to consider enforcement discretion only for a qualified claim saying so. [7] | Promising but limited |
| Type 2 diabetes | A review of 18 trials found modest HbA1c improvement; the authors said the trials were not enough for clinical guidelines. [11] | Promising but limited |
| Migraine prevention | A 2025 meta-analysis of 22 supplement trials found fewer attacks with magnesium (mean difference -2.51). [12] See Magnesium for migraine. | Promising but limited |
| Muscle cramps | A Cochrane review (11 trials, 735 people) judged it unlikely that magnesium gives meaningful cramp prevention in older adults; pregnancy cramp results were conflicting. [13] | No meaningful benefit shown (older adults) |
| Chronic constipation | In 90 adults (mean age 42, 93% women), magnesium oxide 1.5 g for 28 days improved symptoms in 68.3% versus 11.7% with placebo. [14] See the laxative page. | Small trials |
| Sleep | Covered in Magnesium for sleep. | Covered separately |
A change in a test value or symptom score is not the same as preventing a disease. Trial amounts above are study amounts, not recommendations.
Forms and elemental amounts
Supplement Facts labels declare elemental magnesium, not the weight of the whole compound. [7] Forms differ in absorption. [7] One review says oxide supplies a lot of elemental magnesium but is poorly soluble, while organic salts such as citrate dissolve better but supply less per tablet. [15] No form is a universal winner; see Magnesium forms compared and Quality testing and certifications.Medicines and precautions
- Diuretics and proton pump inhibitors can lower magnesium. [1] Magnesium-containing laxatives and antacids can raise it. [9]
- The NHS lists antacids and other indigestion treatments among products that may not mix well with doxycycline and levothyroxine. [16][17] Ask a pharmacist about timing; see Spacing supplements and medicines.
- Kidney disease: MedlinePlus says to tell your doctor about any kidney disease before using magnesium citrate. [2] See Minerals and kidney disease.
- Pregnancy, breastfeeding and children: MedlinePlus gives RDAs of 350 to 360 mg a day for pregnancy at ages 19 to 50. [3] FDA describes the US upper level of 350 mg as covering pregnant and lactating women, and lower levels of 65 mg (ages 1-3) and 110 mg (ages 4-8) for supplemental magnesium. [7] Ask a clinician before supplements.
- Surgery and liver disease: NCCIH says some supplements may affect bleeding or anesthesia, so tell your care team about all of them. [18] Magnesium-specific guidance for surgery or liver disease was not described in the sources we read; ask a clinician or pharmacist.
Testing
MedlinePlus gives a normal blood range of 1.6 to 2.6 mg/dL, and says ranges vary by laboratory. [1] Blood magnesium may be normal even when stores are low, because the body takes magnesium from bone to keep blood levels stable. [9] See Deficiency testing and its limits.Frequently asked questions
How much magnesium do adults need?
The NHS gives 300 mg a day for men and 270 mg for women aged 19-64; the US RDA is 420 mg and 320 mg for adults 31 and over. [4][3] These are group reference values, not personal doses.
What is the upper limit for magnesium supplements?
It depends on the authority: 350 mg a day for ages over 8 (US, Institute of Medicine) or 250 mg a day for readily dissociable salts (EFSA). [7][8] The NHS says 400 mg or less a day from supplements is unlikely to cause harm. [4]
Does magnesium lower blood pressure?
A meta-analysis found reductions of about 2 mm Hg systolic. [10] FDA described the evidence as inconsistent and inconclusive. [7]
Why can magnesium cause diarrhea?
FDA lists osmotic diarrhea, nausea and abdominal cramping as effects of magnesium from non-food sources. [7]
Is magnesium safe with kidney disease?
Not without medical advice. High blood magnesium mostly occurs in people with kidney failure. [9]
References
- MedlinePlus (US National Library of Medicine). Review date 5/19/2025. MedlinePlus Medical Encyclopedia, Magnesium deficiency. Read 2026-10-22.
- MedlinePlus (US National Library of Medicine), drug information; last revised 04/15/2019. MedlinePlus, Magnesium Citrate. Read 2026-10-22.
- MedlinePlus (US National Library of Medicine). Review date 1/21/2025. MedlinePlus Medical Encyclopedia, Magnesium in diet. Read 2026-10-22.
- NHS (UK). Page last reviewed 3 August 2020 (scheduled review date has passed). NHS, Vitamins and minerals: Others (magnesium, phosphorus, potassium, salt). Read 2026-10-22.
- European Food Safety Authority (EU), version 4, September 2017. EFSA, Overview on Dietary Reference Values for the EU population (September 2017). Read 2026-10-22.
- US Food and Drug Administration. FDA, Daily Value on the Nutrition and Supplement Facts Labels. Read 2026-10-22.
- US Food and Drug Administration, letter responding to a qualified health claim petition (Docket FDA-2016-Q-3770); the letter cites sources accessed in 2021. FDA letter on a qualified health claim for magnesium and reduced risk of high blood pressure. Read 2026-10-22.
- European Food Safety Authority (EU), compendium of Scientific Committee on Food opinions (2006); the magnesium opinion was expressed on 26 September 2001. EFSA / Scientific Committee on Food, Tolerable Upper Intake Levels for Vitamins and Minerals. Read 2026-10-22.
- MedlinePlus (US National Library of Medicine). MedlinePlus, Magnesium Blood Test. Read 2026-10-22.
- Effects of Magnesium Supplementation on Blood Pressure: A Meta-Analysis of Randomized Double-Blind Placebo-Controlled Trials. Hypertension 2016. PubMed 27402922. Read 2026-10-22.
- The effects of oral magnesium supplementation on glycaemic control in patients with type 2 diabetes: a systematic review and dose-response meta-analysis of controlled clinical trials. Br J Nutr 2022. PubMed 35045911. Read 2026-10-22.
- Effects of selected dietary supplements on migraine prophylaxis: a systematic review and dose-response meta-analysis of randomized controlled trials. Neurol Sci 2025. PubMed 39404918. Read 2026-10-22.
- Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev 2020. PubMed 32956536. Read 2026-10-22.
- Senna Versus Magnesium Oxide for the Treatment of Chronic Constipation: A Randomized, Placebo-Controlled Trial. Am J Gastroenterol 2021. PubMed 32969946. Read 2026-10-22.
- Open-access article indexed in PubMed Central. Predicting and Testing Bioavailability of Magnesium Supplements (Nutrients 2019, PMC6683096). Read 2026-10-22.
- NHS (UK). Page last reviewed 5 September 2025. NHS Medicines, Doxycycline. Read 2026-10-22.
- NHS (UK). Page last reviewed 6 July 2026. NHS Medicines, Levothyroxine. Read 2026-10-22.
- National Center for Complementary and Integrative Health (US), last updated January 2019. NCCIH, Using Dietary Supplements Wisely. Read 2026-10-22.