Short answer. Adults need 310 to 420 mg of magnesium a day and children aged 1 to 13 need 80 to 240 mg, according to the NIH Office of Dietary Supplements. The adult upper limit for magnesium from supplements is 350 mg a day. Citrate and chelated forms are absorbed better than magnesium oxide in small studies.
Magnesium supplement forms at a glance
| Form | What the studies show | What to know |
|---|---|---|
| Magnesium citrate | More soluble than oxide; gave the highest blood magnesium in a 60-day trial of 46 adults | Dissolves well |
| Magnesium glycinate (bisglycinate chelate) | An amino acid chelate beat oxide at 60 days in the same trial; bisglycinate was better tolerated than oxide in a 12-person study | Bound to the amino acid glycine |
| Magnesium chloride, lactate, aspartate | Absorbed equally well, and much better than oxide, in normal volunteers | Chloride is among the forms most often linked to loose stools |
| Magnesium oxide | About 4% absorbed in one study; no different from placebo in another | Often linked to loose stools |
| Magnesium L-threonate, malate, orotate | Human trials of threonate used blends; no human absorption comparison found for malate or orotate | Too little data to rank them |
| Every form | The label lists elemental magnesium, the amount of the mineral itself, not the weight of the whole compound (NIH ODS) | |
Source: NIH Office of Dietary Supplements; Walker 2003 (PMID 14596323); Firoz 2001 (PMID 11794633); Lindberg 1990 (PMID 2407766); Schuette 1994 (PMID 7815675).
What does magnesium do in the body?
Magnesium is a mineral that more than 300 enzyme systems depend on, including those that make protein, keep muscles and nerves working, and help regulate blood glucose and blood pressure. It is needed to produce energy, to build bone and to make DNA. It also helps move calcium and potassium across cell membranes, which matters for nerve signals, muscle contraction and a normal heart rhythm (NIH Office of Dietary Supplements).
An adult body holds about 25 grams of magnesium, 50% to 60% of it in bone. Less than 1% is in the blood, and the kidneys keep that level in a narrow range (NIH Office of Dietary Supplements).
How much magnesium do children and adults need?
The Recommended Dietary Allowance (RDA) covers food, drinks and supplements combined. The upper limit (UL) is unusual: it applies only to magnesium from supplements and medicines, not to magnesium in food and water, which is why for some ages it is lower than the RDA.
| Age | Boys and men | Girls and women | Upper limit from supplements |
|---|---|---|---|
| 0–6 months | 30 mg (Adequate Intake) | 30 mg (Adequate Intake) | Not established |
| 7–12 months | 75 mg (Adequate Intake) | 75 mg (Adequate Intake) | Not established |
| 1–3 years | 80 mg | 80 mg | 65 mg |
| 4–8 years | 130 mg | 130 mg | 110 mg |
| 9–13 years | 240 mg | 240 mg | 350 mg |
| 14–18 years | 410 mg | 360 mg | 350 mg |
| 19–30 years | 400 mg | 310 mg | 350 mg |
| 31 years and older | 420 mg | 320 mg | 350 mg |
| Pregnancy | — | 400 mg (14–18), 350 mg (19–30), 360 mg (31–50) | 350 mg |
| Lactation | — | 360 mg (14–18), 310 mg (19–30), 320 mg (31–50) | 350 mg |
Source: NIH Office of Dietary Supplements.
The Daily Value on labels is 420 mg for adults and children 4 and older. For young children the supplement limit is low: 65 mg at ages 1 to 3 and 110 mg at ages 4 to 8. Many adult products carry more in one serving, so a child's dose belongs with the pediatrician.
Do most people get enough magnesium from food?
Many do not. In national survey data from 2013 to 2016, 48% of Americans of all ages got less magnesium from food and drinks than the average requirement for their age. Teenage boys and girls and men aged 71 and older were the most likely to fall short (NIH Office of Dietary Supplements).
| Food and serving | Magnesium, mg |
|---|---|
| Pumpkin seeds, roasted, 1 ounce | 156 |
| Almonds, dry roasted, 1 ounce | 80 |
| Spinach, boiled, ½ cup | 78 |
| Black beans, cooked, ½ cup | 60 |
| Rice, brown, cooked, ½ cup | 42 |
| Banana, 1 medium | 32 |
| Milk, 1 cup | 27 |
Source: NIH Office of Dietary Supplements.
Seeds, nuts, beans, leafy greens and whole grains are the richest sources; refining grains strips much of it. Water adds some too, from 1 mg to more than 120 mg per liter depending on the source. The body typically absorbs about 30% to 40% of the magnesium in food (NIH Office of Dietary Supplements).
Who is most likely to run low on magnesium?
According to the NIH:
- Teenagers and older adults, who most often eat too little; with age the gut also absorbs less.
- People with digestive conditions that cause long-lasting diarrhea or poor fat absorption, or who have had surgery on the small intestine.
- People who drink heavily.
- People who take certain medicines for a long time, such as some diuretics and acid-reducing drugs (see below).
True deficiency from diet alone is uncommon in healthy people, because the kidneys hold on to magnesium. Early signs include loss of appetite, nausea, tiredness and weakness, later numbness, tingling and muscle cramps (NIH Office of Dietary Supplements). None is specific to magnesium, so they are reasons to see a doctor, not to start a supplement on your own.
Testing is hard. Most magnesium sits inside cells and bone, so serum magnesium (normal range 0.75 to 0.95 mmol/L) says little about total stores, and no single test is considered satisfactory. A doctor may combine lab results with diet and symptoms (NIH Office of Dietary Supplements).
Which form of magnesium is best absorbed?
Forms that dissolve well in liquid are absorbed more completely; small studies found aspartate, citrate, lactate and chloride absorbed better than oxide and sulfate (NIH Office of Dietary Supplements). The individual studies:
- Citrate versus oxide. Magnesium oxide barely dissolved in water in lab tests, while citrate was 55% soluble. In volunteers, urinary magnesium rose far more after citrate than after the same dose of oxide (Lindberg 1990).
- Citrate, chelate and oxide over 60 days. In a randomized, double-blind trial, 46 healthy adults took 300 mg a day as a chelate, citrate, oxide or placebo. Citrate and the chelate were absorbed better than oxide, citrate produced the highest blood levels, and oxide did no better than placebo (Walker 2003).
- Chloride, lactate and aspartate. In normal volunteers these three were absorbed equally well, while only about 4% of magnesium oxide was absorbed (Firoz 2001).
- Glycinate. In a crossover study of 12 adults who had had part of the small intestine removed, absorption of 100 mg of magnesium was similar overall for bisglycinate and oxide, but was twice as high from bisglycinate in the four people who absorbed oxide most poorly, and every participant tolerated bisglycinate better (Schuette 1994).
Human threonate trials used blends; a 30-day trial in 109 healthy adults combined it with phosphatidylserine and vitamins, so it cannot show how threonate alone compares with other forms (Zhang 2022). We found no human study on PubMed that compares how well malate or orotate is absorbed against other forms.
A practical way to choose: avoid relying on magnesium oxide alone, pick a form the person tolerates, and compare products by the elemental magnesium on the label.
When and how should you take magnesium?
The size of each dose matters. In a study of magnesium taken with a standard meal, the body absorbed 65% of the smallest dose but only 11% of the largest, so the extra magnesium in a big single dose is absorbed less efficiently (Fine 1991). This is one reason some labels suggest splitting the daily amount across meals. An enteric-coated tablet was also absorbed much less than an uncoated form.
Very high zinc gets in the way: 142 mg of zinc a day significantly lowered magnesium absorption in men (Spencer 1994). That is far above the adult zinc limit of 40 mg; see our zinc guide.
Can you take too much magnesium?
From food, no: healthy kidneys remove the excess. From supplements and medicines, yes: high doses often cause diarrhea, sometimes with nausea and cramps. The forms most often reported to cause diarrhea are magnesium carbonate, chloride, gluconate and oxide, because unabsorbed magnesium draws water into the gut (NIH Office of Dietary Supplements).
Serious toxicity is rare and has involved very large doses of laxatives and antacids, typically above 5,000 mg a day, including a fatal case in a 28-month-old boy. Signs include low blood pressure, nausea, lethargy and muscle weakness, and the risk is higher when the kidneys are not working well (NIH Office of Dietary Supplements).
Antacids and laxatives count toward the upper limit. One tablespoon of milk of magnesia carries 500 mg of magnesium, and an extra-strength Rolaids tablet 55 mg (NIH Office of Dietary Supplements). Add up every source and compare the total with the limit for the person's age.
Does magnesium interact with medicines?
The NIH lists these:
- Oral bisphosphonates, such as alendronate. Magnesium lowers their absorption; take them at least 2 hours apart.
- Tetracycline and quinolone antibiotics, such as doxycycline, demeclocycline, ciprofloxacin and levofloxacin. Take the antibiotic at least 2 hours before or 4 to 6 hours after a magnesium supplement.
- Diuretics. Loop diuretics such as furosemide and bumetanide, and thiazide diuretics such as hydrochlorothiazide, increase magnesium lost in urine. Potassium-sparing diuretics such as amiloride and spironolactone reduce it.
- Proton pump inhibitors, such as esomeprazole and lansoprazole, can lower blood magnesium when taken for more than about a year. The FDA advises doctors to consider checking magnesium before and during long-term use.
Which ASDHelp products contain magnesium?
Doses are copied from each label (elemental magnesium). Supplement limits: 65 mg at ages 1 to 3, 110 mg at 4 to 8, 350 mg from 9.
- Magnesium Night: 300 mg per 6 g scoop, as magnesium orotate, magnesium glycerophosphate and TRAACS magnesium bisglycinate chelate (100 mg each), with botanicals. Label directions: one scoop in 8 ounces of water a day, 30 to 60 minutes before bedtime. 300 mg is above the upper limit for ages 1 to 8.
- Magnesium L-Threonate+ Powder: 200 mg per scoop, as di-magnesium malate, magnesium L-threonate (1 g of Magtein) and magnesium lysinate glycinate chelate. Label directions: one scoop in 4 ounces of water once or twice a day. One scoop is above the upper limit for ages 1 to 8; two scoops (400 mg) are above the 350 mg limit for older children and adults.
- Brain Mag: 145 mg per 3 capsules, from 2 g of Magtein magnesium L-threonate. Label directions: 3 capsules a day, divided, for example one with each meal. 145 mg is above the upper limit for ages 1 to 8.
- Mag-B6: 100 mg per capsule as TRAACS magnesium bisglycinate chelate and magnesium oxide, with 30 mg of vitamin B6 as P-5-P. Label directions: adults, 1 capsule a day with food; children as directed by a healthcare professional. 100 mg is above the 65 mg limit for ages 1 to 3.
- Formula C: 100 mg per 6 capsules as TRAACS bisglycinate chelate and oxide, inside a multivitamin. Label directions: adults or children 4 and older, 6 capsules a day with food.
- Brain Calm: 75 mg per 2 capsules as di-magnesium malate, in a formula with GABA, L-theanine and 5-HTP. Label directions: 2 capsules a day; no children's dose on the label. 75 mg is above the 65 mg limit for ages 1 to 3.
Questions to take to your doctor
- Given our diet, is a magnesium supplement worth considering, and is any test useful when serum magnesium reflects body stores so poorly?
- How much magnesium do all of our current products and any antacids or laxatives add up to, and how does that compare with the supplement limit for each person's age?
- Which form suits a sensitive stomach, and should the daily amount be split across meals?
- Do any of our medicines, such as an antibiotic, a diuretic, an acid-reducing drug or a bone medicine, call for separate timing or monitoring?
Sources
- NIH Office of Dietary Supplements. Magnesium fact sheet for health professionals. ods.od.nih.gov
- National Academies. Dietary Reference Intakes tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Walker AF et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res 2003. PMID 14596323
- Lindberg JS et al. Magnesium bioavailability from magnesium citrate and magnesium oxide. J Am Coll Nutr 1990. PMID 2407766
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res 2001. PMID 11794633
- Schuette SA et al. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN 1994. PMID 7815675
- Fine KD et al. Intestinal absorption of magnesium from food and supplements. J Clin Invest 1991. PMID 1864954
- Spencer H et al. Inhibitory effects of zinc on magnesium balance and magnesium absorption in man. J Am Coll Nutr 1994. PMID 7836627
- Zhang C et al. A Magtein, magnesium L-threonate, based formula improves brain cognitive functions in healthy Chinese adults. Nutrients 2022. PMID 36558392
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.