Lab result explainedVitamins and mineralsLast updated November 8, 2026

Magnesium blood test: what low and high magnesium levels mean, and why serum magnesium can miss a deficiency

Magnesium (serum) (Mg) · Often ordered alone or added to a metabolic panel; part of many 'electrolyte' or 'renal' profiles · reported in mg/dL (mmol/L in many countries; mEq/L on some older reports). 1 mg/dL = 0.41 mmol/L = 0.82 mEq/L.

Magnesium is a mineral that more than 300 enzymes depend on, including those that make and use ATP, control muscle and nerve excitability, keep heart rhythm steady and regulate potassium and calcium. A serum magnesium blood test measures the magnesium dissolved in the liquid part of your blood. Normal is roughly 1.7 to 2.2 mg/dL (0.70 to 0.90 mmol/L), although ranges differ between labs and some run from 1.6 to 2.6.

The test has a well-known blind spot. Only about 1 percent of the body's magnesium is in blood; more than half is in bone and most of the rest is inside cells. The body defends the blood level by pulling magnesium out of bone, so a person can be genuinely depleted at the tissue level while the serum value sits in the lower half of normal. Researchers have argued that the lower limit should be closer to 2.0 mg/dL (0.85 mmol/L), and about half of Americans eat less magnesium than the estimated average requirement. A red blood cell (RBC) magnesium is sometimes offered as a closer look at intracellular stores, but it is less standardised and has not been shown to predict outcomes better.

Low magnesium is the common problem. Proton pump inhibitors taken for more than a year, loop and thiazide diuretics, heavy alcohol use, chronic diarrhoea, poorly controlled diabetes and some chemotherapy drugs are the leading causes, and low magnesium drags potassium and calcium down with it. High magnesium is rare and essentially confined to people with kidney failure who take magnesium-containing antacids, laxatives or supplements, or to women receiving intravenous magnesium for pre-eclampsia.

Mg at a glance

  • What it is: the concentration of magnesium in blood serum; only about 1 percent of body magnesium, so a normal value does not rule out deficiency.
  • Normal: about 1.7–2.2 mg/dL (0.70–0.90 mmol/L; 1.4–1.8 mEq/L). Labs differ; some use 1.6–2.6. Values below 2.0 may already reflect low body stores.
  • Low (hypomagnesemia): below 1.7 mg/dL. Symptoms (tremor, cramps, palpitations) usually appear below 1.2 mg/dL; low potassium and calcium that will not correct are classic clues.
  • High (hypermagnesemia): above 2.2–2.6 mg/dL. Nearly always kidney failure plus a magnesium source. Reflexes disappear above about 4–5 mg/dL; breathing and heart problems above 7–10.
  • Common causes of low: proton pump inhibitors, diuretics, alcohol, diarrhoea or malabsorption, diabetes, cisplatin, low dietary intake.
  • Next step: check potassium, calcium and kidney function, review medicines and alcohol, increase magnesium-rich foods or take a well-absorbed supplement (citrate, glycinate, malate) and recheck in 4 to 8 weeks.

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What Mg measures

The serum magnesium assay measures total magnesium in blood serum by a colorimetric method, reported in the United States in milligrams per decilitre (mg/dL); many other countries use millimoles per litre (multiply mg/dL by 0.41) and older reports use milliequivalents per litre (multiply mg/dL by 0.82). About 30 percent of serum magnesium is bound to albumin, so very low albumin lowers the total slightly; the rest is free (ionised) or complexed and is the biologically active part. A haemolysed sample reads falsely high because red cells contain about three times more magnesium than serum.

An adult body holds about 25 g of magnesium. Roughly 50 to 60 percent is in bone, where it also acts as a reservoir, about 40 percent is inside muscle and other soft-tissue cells, and under 1 percent is in extracellular fluid. The kidneys are the main regulator: they filter about 2,400 mg a day and reabsorb 95 to 99 percent of it, and can cut urinary losses to under 12 mg a day when intake is poor or increase them sharply when magnesium is given. The gut absorbs 30 to 40 percent of what is eaten, more when intake is low and less when it is high, and absorption is reduced by very high calcium or phosphate intake and by low stomach acid.

Because bone and cells buffer the blood level, serum magnesium reflects recent balance better than total stores. People with chronic marginal intake can have normal serum values yet low muscle or bone magnesium, a state sometimes called chronic latent magnesium deficiency. The research standard for detecting this is the magnesium loading (retention) test, in which a measured dose is given intravenously and the proportion kept by the body is calculated; it is rarely used clinically. In practice, a serum level in the bottom part of the range combined with symptoms, a cause (such as a PPI or diuretic) and a low potassium or calcium is treated as deficiency.

Normal range for Mg

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (mg/dL (mmol/L in many countries; mEq/L on some older reports). 1 mg/dL = 0.41 mmol/L = 0.82 mEq/L.)Notes
Adults, typical reference range1.7–2.2 mg/dL (0.70–0.90 mmol/L)Labs vary: 1.6–2.6, 1.8–2.4 and 1.8–2.6 mg/dL are all in use. Use the printed range.
Proposed evidence-based lower limit2.0 mg/dL (0.85 mmol/L)Several research groups argue that values of 1.7–2.0 often represent deficiency, based on loading tests and outcome data. Not yet adopted by most labs.
Mild hypomagnesemia1.2–1.7 mg/dLUsually no specific symptoms. Low potassium and calcium that fail to correct are the usual clue. Oral replacement and treating the cause.
Moderate to severe hypomagnesemiaBelow 1.2 mg/dL (0.5 mmol/L)Tremor, muscle twitching, cramps, tetany, palpitations, arrhythmia (including torsades de pointes) and seizures. Usually intravenous replacement.
Mild hypermagnesemia2.3–4.0 mg/dLUsually asymptomatic. Check kidney function and stop magnesium antacids, laxatives and supplements.
Moderate hypermagnesemia4–7 mg/dLNausea, flushing, drowsiness, low blood pressure, loss of deep tendon reflexes. Intravenous magnesium for pre-eclampsia is deliberately kept at about 5–8 mg/dL with reflex monitoring.
Severe hypermagnesemiaAbove 7–10 mg/dLMuscle paralysis, respiratory depression, heart block; cardiac arrest can occur above about 12 mg/dL. Treated with IV calcium and dialysis.
ChildrenAbout 1.7–2.3 mg/dLSlightly higher than adults in infancy; newborn ranges differ again.
RBC magnesium (where offered)About 4.2–6.8 mg/dLMeasures magnesium inside red cells. Ranges and methods are not standardised between labs and clinical validation is limited.

High magnesium (hypermagnesemia)

A magnesium above the lab's upper limit (usually 2.2 to 2.6 mg/dL) is uncommon, because healthy kidneys excrete surplus magnesium rapidly. When it happens, the near-universal background is reduced kidney function (an eGFR below 30, acute kidney injury or dialysis) combined with a magnesium source: antacids such as milk of magnesia, magnesium-containing laxatives and enemas, Epsom salt baths or drinks, or supplements. In a person with normal kidneys, a mildly high result is most often a haemolysed sample, mild dehydration or a transient effect of a recent large dose, and a repeat is normal.

Other causes are rare: intravenous magnesium for pre-eclampsia or severe asthma (where the high level is intentional and monitored), lithium treatment, untreated hypothyroidism, Addison's disease, tumour lysis and the familial condition hypocalciuric hypercalcaemia. Magnesium levels between 2.5 and 4 mg/dL rarely cause symptoms. Above about 4 to 5 mg/dL the deep tendon reflexes fade, which clinicians use as a bedside gauge, and above 7 to 10 mg/dL muscle weakness progresses to respiratory depression, heart block and, at very high levels, cardiac arrest.

Magnesium also competes with calcium, so hypermagnesemia lowers blood pressure, slows the heart and can cause a low calcium reading. For most readers the practical message is that over-the-counter magnesium is safe with normal kidneys but should be cleared with a clinician if eGFR is below 30 to 45.

Common causes

  1. Kidney failure plus a magnesium source

    Chronic kidney disease (eGFR below 30), acute kidney injury or dialysis removes the body's main way of excreting magnesium; antacids, laxatives, enemas or supplements then accumulate. Accounts for the great majority of significant hypermagnesemia.

  2. Magnesium-containing antacids, laxatives and enemas

    Milk of magnesia, magnesium citrate bowel preparations, some antacid tablets and Epsom salt (magnesium sulfate) drinks or enemas deliver grams of magnesium. Fatal cases are described in older adults with constipation and unrecognised kidney impairment.

  3. Intravenous magnesium therapy

    Used for pre-eclampsia and eclampsia, severe asthma and torsades de pointes, aiming for 5 to 8 mg/dL; reflexes, breathing and urine output are monitored to prevent toxicity, which is treated with calcium gluconate.

  4. Haemolysed sample or dehydration

    Red cells contain more magnesium than serum, so a haemolysed draw reads high; dehydration concentrates it slightly. Both produce mild, transient elevations that normalise on repeat.

  5. Lithium, hypothyroidism and Addison's disease

    Lithium reduces renal magnesium excretion; low thyroid hormone and low cortisol both mildly raise magnesium through reduced clearance.

  6. Tumour lysis, rhabdomyolysis and diabetic ketoacidosis

    Massive cell breakdown releases intracellular magnesium along with potassium and phosphate; in DKA, acidosis shifts magnesium out of cells, and the level falls once insulin is started.

  7. Familial hypocalciuric hypercalcaemia

    An inherited calcium-sensing receptor variant causes mild, harmless elevation of both calcium and magnesium that needs no treatment but is often mistaken for hyperparathyroidism.

Symptoms that can go with it

  • None at mildly raised levels (up to about 4 mg/dL)
  • Nausea, vomiting and facial flushing
  • Drowsiness, lethargy, confusion
  • Low blood pressure and a slow heartbeat
  • Loss of deep tendon reflexes (knee and ankle jerks)
  • Muscle weakness progressing to paralysis and slow, shallow breathing
  • Heart block or cardiac arrest at very high levels

Low magnesium (hypomagnesemia)

A magnesium below about 1.7 mg/dL means your body is losing magnesium faster than it is absorbing it, and because serum is defended by bone stores, a frankly low value usually implies a substantial tissue deficit. The causes divide into gut losses and poor absorption (chronic diarrhoea, coeliac disease, Crohn's disease, bowel resection, bariatric surgery, long-term proton pump inhibitors, low dietary intake and alcohol), kidney losses (loop and thiazide diuretics, poorly controlled diabetes with glucose in the urine, alcohol again, cisplatin, cetuximab, cyclosporine and tacrolimus, aminoglycosides, amphotericin, Gitelman syndrome, hyperaldosteronism) and shifts into bone or cells (refeeding, treatment of DKA, acute pancreatitis, 'hungry bone' after parathyroid surgery).

Low magnesium rarely travels alone. It causes kidney potassium wasting, so around 40 percent of people with low potassium are also magnesium-deficient and their potassium will not correct until magnesium is replaced. It suppresses parathyroid hormone release and blocks its action, producing a low calcium that likewise resists calcium supplements. Symptoms reflect over-excitable nerves and muscles: tremor, twitching, cramps, a positive Chvostek or Trousseau sign, tetany, and at lower levels seizures, confusion and heart rhythm disturbances, including the dangerous torsades de pointes. Most cases above 1.2 mg/dL cause no symptoms and are found on routine testing or while investigating low potassium.

The serum test under-detects deficiency, so clinicians increasingly act on values in the low-normal band (1.7 to 2.0 mg/dL) when there is a plausible cause and compatible symptoms, and on a low urinary magnesium, which shows that the kidneys are conserving. Population studies link low magnesium intake and low-normal serum levels to higher rates of type 2 diabetes, hypertension, coronary disease, atrial fibrillation and migraine, though trials of supplementation show modest effects, largest in people who start out deficient.

Common causes

  1. Proton pump inhibitors (omeprazole, esomeprazole, pantoprazole, lansoprazole)

    Long-term use, usually over a year, impairs intestinal magnesium absorption; a meta-analysis found PPI users had about 43 percent higher odds of hypomagnesemia, and the FDA issued a safety warning in 2011. Levels recover within one to two weeks of stopping and fall again within days of restarting.

  2. Loop and thiazide diuretics

    Furosemide, bumetanide, hydrochlorothiazide and chlorthalidone increase urinary magnesium loss; the effect is modest with low doses but adds to other causes and is a common reason for low magnesium with low potassium in older adults.

  3. Alcohol use disorder

    Alcohol increases urinary magnesium excretion, and poor diet, vomiting, diarrhoea and pancreatitis compound it. Roughly 30 percent of people with alcohol use disorder are hypomagnesemic, and magnesium replacement is routine during withdrawal.

  4. Chronic diarrhoea and malabsorption

    Coeliac disease, Crohn's disease, ulcerative colitis, short bowel, chronic pancreatitis, bariatric surgery and laxative misuse all reduce absorption or increase losses; diarrhoeal fluid contains considerable magnesium.

  5. Poorly controlled diabetes

    Glucose spilling into urine drags magnesium with it and insulin resistance reduces cellular uptake; 14 to 48 percent of people with type 2 diabetes are hypomagnesemic, and low magnesium in turn worsens insulin resistance.

  6. Low dietary intake

    About 48 percent of Americans eat less than the estimated average requirement, with intake lowest among older adults and people eating few whole grains, legumes, nuts and vegetables. Diet alone rarely produces a frankly low serum level but sets the stage when any loss is added.

  7. Chemotherapy and immunosuppressants

    Cisplatin causes renal magnesium wasting in most people treated and can persist for years; the EGFR antibodies cetuximab and panitumumab, cyclosporine, tacrolimus, aminoglycosides, amphotericin B, pentamidine and foscarnet all do the same.

  8. Hyperaldosteronism, hypercalcaemia and inherited tubular disorders

    Excess aldosterone and high calcium both increase renal magnesium loss; Gitelman and Bartter syndromes are inherited tubular defects presenting with low magnesium and low potassium, often in young adults.

  9. Refeeding, acute pancreatitis and 'hungry bone' syndrome

    Rapid cell growth during refeeding, saponification of fat in pancreatitis and bone remineralisation after parathyroid surgery pull magnesium out of the blood quickly.

  10. Pregnancy and breastfeeding

    Expanded blood volume, increased renal filtration and fetal demand lower serum magnesium slightly in the second and third trimesters; most values stay within range but intake needs rise.

Symptoms that can go with it

  • Often none when magnesium is 1.2 to 1.7 mg/dL
  • Muscle cramps, twitching, tremor or eyelid flickering
  • Fatigue, weakness and loss of appetite
  • Nausea or vomiting
  • Numbness, tingling or spasms of the hands and feet (tetany) when calcium is also low
  • Palpitations or an irregular heartbeat
  • Confusion, personality change or seizures at very low levels

Read it alongside

  • Potassium — low potassium that will not correct is the classic clue to low magnesium; about 40 percent of people with hypokalemia are also magnesium-deficient.
  • Calcium — low magnesium suppresses parathyroid hormone and causes a low calcium that resists calcium replacement; high magnesium can also lower calcium.
  • Creatinine and eGFR — kidney function determines both the risk of high magnesium and how safely supplements can be taken.
  • Phosphorus — low with magnesium in refeeding, alcohol misuse and DKA treatment; high with magnesium in kidney failure and tumour lysis.
  • Glucose and A1C — poorly controlled diabetes wastes magnesium, and low magnesium worsens insulin resistance.
  • Albumin — about 30 percent of serum magnesium is albumin-bound, so very low albumin modestly lowers the total.
  • Urine magnesium (24-hour or fractional excretion) — above about 2 percent fractional excretion with low serum magnesium means the kidneys are wasting it (diuretics, alcohol, drugs); below that means gut losses or poor intake.
  • Parathyroid hormone and vitamin D — low magnesium blunts PTH and impairs activation of vitamin D, which can masquerade as hypoparathyroidism or vitamin D resistance.

What usually happens next

  1. A mildly low or low-normal magnesium (1.5 to 2.0 mg/dL) in someone who feels well is usually handled by reviewing PPIs, diuretics, alcohol and diet, increasing magnesium-rich foods or starting an oral supplement, and rechecking in 4 to 8 weeks together with potassium and calcium.
  2. If a PPI is the likely cause, ask whether the dose can be reduced, switched to an H2 blocker (famotidine) or stopped; magnesium often recovers within two weeks of stopping and supplements alone may not keep up while the PPI continues.
  3. Below about 1.2 mg/dL, or at any level with tremor, tetany, palpitations or seizures, expect intravenous magnesium in hospital with an ECG and checks of potassium and calcium, because oral replacement is too slow and causes diarrhoea at the doses needed.
  4. Persistent or recurrent low magnesium without an obvious cause is investigated with a 24-hour urine or fractional excretion of magnesium to separate kidney wasting from gut loss, followed by coeliac serology, stool studies or renin and aldosterone as the pattern suggests.
  5. A high magnesium is repeated on a non-haemolysed sample with a creatinine; if confirmed, all magnesium-containing antacids, laxatives and supplements are stopped and, with poor kidney function or symptoms, hospital treatment with fluids, calcium and sometimes dialysis follows.
  6. Ask whether a normal serum result fully answers your question: if you have symptoms and a cause, a therapeutic trial of magnesium for 4 to 8 weeks or a 24-hour urine magnesium may be more informative than the single serum value.

Diet, lifestyle and natural levers with evidence

What can move Mg once the cause is known. Nothing here replaces finding the cause.

Magnesium-rich foods: nuts, seeds, legumes, whole grains, leafy greens

Strong evidence

Pumpkin seeds (about 150 mg per ounce), almonds (80 mg), spinach (80 mg per half cup cooked), black beans (60 mg per half cup), whole grains, dark chocolate and mineral-rich water are the main sources, and 30 to 40 percent of dietary magnesium is absorbed. Recommended intakes are 400 to 420 mg a day for men and 310 to 320 mg for women. In pooled cohort studies, each additional 100 mg a day of dietary magnesium is associated with 8 to 14 percent lower risk of type 2 diabetes and about 7 percent lower risk of stroke, and dietary magnesium is the preferred route in kidney disease because intake is self-limiting.

Oral magnesium supplements: which form and how much

Moderate evidence

A meta-analysis of 34 randomised trials (median dose 368 mg a day for 3 months) found supplementation raised serum magnesium by about 0.05 mmol/L (0.12 mg/dL) and lowered blood pressure by about 2 mmHg systolic. Organic salts are better absorbed than magnesium oxide: in a 60-day randomised comparison, magnesium citrate produced higher serum and salivary levels than oxide or an amino-acid chelate, and in a single-dose study oxide was about 4 percent absorbed. Citrate, glycinate (bisglycinate), malate and lactate are the usual choices; glycinate causes less diarrhoea, and threonate has early human data for cognition but none showing an advantage for correcting deficiency. Splitting 200 to 400 mg of elemental magnesium across the day improves absorption and tolerance.

The tolerable upper intake for supplemental magnesium is 350 mg a day of elemental magnesium for adults without a diagnosed deficiency; diarrhoea is the usual sign of excess. People with an eGFR below 30 should not take magnesium without medical supervision. Magnesium binds tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine; separate doses by at least 2 to 4 hours.

Reduce alcohol intake

Strong evidence

Alcohol causes the kidneys to waste magnesium within hours of drinking and is combined with poor intake, vomiting and diarrhoea in heavy drinkers, about 30 percent of whom have frank hypomagnesemia. Serum and muscle magnesium recover within weeks of abstinence, and magnesium replacement is a routine part of treating alcohol withdrawal because deficiency contributes to tremor, arrhythmia and seizures.

Improve blood sugar control

Moderate evidence

High blood glucose pulls magnesium out through the kidneys, so better glycaemic control reduces losses. The relationship runs both ways: a meta-analysis of 18 randomised trials found that magnesium supplementation (mostly 250 to 450 mg a day for 6 to 24 weeks) lowered fasting glucose in people with diabetes and improved insulin sensitivity in people at high risk, with the largest effect in those who were magnesium-deficient to begin with. Dietary magnesium intake is inversely related to the risk of developing type 2 diabetes in every major cohort.

Check vitamin D and magnesium together

Preliminary evidence

Magnesium is a cofactor for the enzymes that activate vitamin D, and in a randomised trial magnesium supplementation raised 25-hydroxyvitamin D when baseline levels were below 30 ng/mL and lowered it when levels were already above 30 to 50, suggesting it helps normalise vitamin D status. Observational data show that the benefits of vitamin D on mortality and bone are strongest in people with adequate magnesium. High-dose vitamin D without adequate magnesium may also increase calcium without the expected benefit. Evidence is still early and comes mainly from one trial and cohort studies.

Limit very high-dose calcium and zinc supplements taken at the same time

Preliminary evidence

Calcium and magnesium share intestinal transport, and supplemental zinc above about 140 mg a day reduced magnesium absorption and balance in a small controlled study. Calcium supplements of 1,000 mg or more taken with magnesium reduce its absorption modestly. Taking magnesium at a different time of day from large calcium or zinc doses, and keeping calcium supplements to what diet does not supply, is a reasonable precaution with limited but consistent evidence.

When to see a clinician promptly

  • A magnesium below 1.2 mg/dL, or any low result with muscle spasms, tremor, palpitations, an irregular pulse, confusion or a seizure: needs same-day assessment and usually intravenous replacement.
  • A magnesium above 4 mg/dL, or any high result with weakness, drowsiness, nausea, slow pulse or loss of reflexes, particularly if you have kidney disease or have been taking magnesium laxatives or antacids.
  • Low magnesium together with low potassium or low calcium that has not corrected with replacement, which usually means the magnesium needs to be fixed first.
  • Low magnesium if you take a proton pump inhibitor, so the need for the drug can be reviewed, or if you are on cisplatin, cetuximab, tacrolimus or cyclosporine, where monitoring and replacement are routine.
  • Recurrent unexplained low magnesium with low potassium in a young adult, or with high blood pressure, which can point to Gitelman syndrome or hyperaldosteronism.
  • Persistent symptoms suggestive of deficiency (cramps, twitching, palpitations, fatigue) with a cause such as diarrhoea, alcohol or diuretics, even when the serum value is low-normal.

Frequently asked questions

What is a normal magnesium level in a blood test?

Most US labs give a reference range of about 1.7 to 2.2 mg/dL, though some use 1.6 to 2.6 or 1.8 to 2.4. In mmol/L the usual range is 0.70 to 0.90. Several research groups argue that values below 2.0 mg/dL (0.85 mmol/L) often reflect deficiency, so a result of 1.8 that is 'normal' on the printout may still be worth acting on if you have symptoms and a cause such as a PPI, diuretic or diarrhoea.

Is a magnesium level of 1.6 or 1.7 low?

A magnesium of 1.6 mg/dL is below the lower limit on most labs and counts as mild hypomagnesemia; 1.7 is at the lower limit. Neither usually causes symptoms, but both suggest that body stores are reduced, since the blood level is defended by bone. The usual response is to look for a cause (medicines, alcohol, diarrhoea, diabetes, low intake), check potassium and calcium, increase magnesium-rich foods or take a supplement, and recheck in a month or two.

Why can a serum magnesium test miss a deficiency?

Because only about 1 percent of the body's magnesium is in blood and the body pulls magnesium from bone to keep that level steady. Someone with depleted muscle and bone stores can therefore have a serum value in the lower half of normal. A low-normal result with symptoms and a cause, a low 24-hour urine magnesium, or improvement with a trial of supplementation are the practical ways around this; the research gold standard, a magnesium loading test, is rarely done.

Serum magnesium vs RBC magnesium: which test is better?

Serum magnesium is the standard, validated test and the one all guidelines and treatment thresholds are based on. RBC magnesium measures magnesium inside red blood cells, which in principle tracks intracellular stores better, and it is sometimes low when serum is normal. However, reference ranges (roughly 4.2 to 6.8 mg/dL) and methods differ between labs, red cells are not necessarily representative of muscle or heart cells, and no large studies show that treating a low RBC magnesium improves outcomes. It can be a useful supplementary clue but should not override a clinical judgement based on serum level, symptoms and cause.

What are the symptoms of low magnesium?

Mild deficiency usually has no specific symptoms, or vague ones such as fatigue, poor appetite and nausea. As it deepens, nerve and muscle excitability rise: muscle cramps, twitching, eyelid flicker, tremor, tingling and, with low calcium, hand and foot spasms. Palpitations and arrhythmias can occur, and at very low levels confusion and seizures. Because low magnesium drags potassium and calcium down, many of the symptoms blamed on it are really from those.

Do proton pump inhibitors like omeprazole cause low magnesium?

Yes, with long-term use. PPIs reduce intestinal magnesium absorption; the risk rises after about a year and is higher with diuretics or diarrhoea. A pooled analysis found 43 percent higher odds of hypomagnesemia in PPI users, and the FDA added a warning in 2011. Supplements often fail to keep up while the PPI continues, whereas levels recover within one to two weeks of stopping, so the main fix is reviewing whether the PPI is still needed or can be swapped for an H2 blocker.

What is the best form of magnesium supplement to take?

Organic salts such as citrate, glycinate (bisglycinate), malate and lactate are better absorbed than magnesium oxide, which is cheap but only a few percent absorbed and acts mainly as a laxative. Citrate has the best comparative data for raising magnesium levels; glycinate is gentlest on the bowel; threonate has early evidence for brain effects but no advantage for correcting a deficiency. Doses of 200 to 400 mg of elemental magnesium a day, split, are typical, and the upper limit from supplements for people without a diagnosed deficiency is 350 mg.

Can you have too much magnesium?

From food, no: the kidneys excrete the surplus. From supplements, the first sign of excess is diarrhoea, which usually appears above 350 to 400 mg of elemental magnesium a day in people with normal kidneys and limits further absorption. Dangerous hypermagnesemia essentially requires kidney failure plus a large source such as magnesium laxatives, antacids or Epsom salts, and causes drowsiness, low blood pressure, lost reflexes and, above 7 to 10 mg/dL, breathing and heart problems. Anyone with an eGFR below 30 should take magnesium only under supervision.

References

  1. Magnesium blood test. MedlinePlus, US National Library of Medicine (2023)View source
  2. Magnesium: fact sheet for health professionals. National Institutes of Health, Office of Dietary Supplements (2022)View source
  3. Hypomagnesemia. Merck Manual Professional Version (2023)
  4. Hypermagnesemia. Merck Manual Professional Version (2023)
  5. Costello RB, Elin RJ, Rosanoff A, et al.. Perspective: the case for an evidence-based reference interval for serum magnesium: the time has come. Advances in Nutrition (2016)
  6. Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated?. Nutrition Reviews (2012)
  7. Cheungpasitporn W, Thongprayoon C, Kittanamongkolchai W, et al.. Proton pump inhibitors linked to hypomagnesemia: a systematic review and meta-analysis of observational studies. Renal Failure (2015)
  8. Zhang X, Li Y, Del Gobbo LC, et al.. Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension (2016)
  9. Dong JY, Xun P, He K, Qin LQ. Magnesium intake and risk of type 2 diabetes: meta-analysis of prospective cohort studies. Diabetes Care (2011)
  10. Veronese N, Watutantrige-Fernando S, Luchini C, et al.. Effect of magnesium supplementation on glucose metabolism in people with or at risk of diabetes: a systematic review and meta-analysis of double-blind randomized controlled trials. European Journal of Clinical Nutrition (2016)
  11. Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research (2003)
  12. Dai Q, Zhu X, Manson JE, et al.. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. American Journal of Clinical Nutrition (2018)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.