Magnesium: Which Form Is Best and How to Take It

“Give me magnesium, the best one.” I hear this at the pharmacy almost every day. Then the person faces a shelf of twenty bottles: citrate, bisglycinate, oxide, “marine”, with B6, without B6, 500 mg, 1000 mg. And asks: so which one?

The answer depends on why you want it. Below I go through the forms, the doses and what the numbers on the label actually mean.

What magnesium does and how much you need

Magnesium is involved in more than 300 enzymes. Your muscles need it to relax after contracting, and so do your nerves, heart and bones. About 60% of the body’s magnesium sits in the bones, the rest in muscles and soft tissue. Only about 1% is in the blood.

Magnesium is also needed to convert vitamin D into its active form. If you take vitamin D in autumn, check that your diet has enough magnesium as well.

How much? The European Food Safety Authority considers 350 mg a day adequate for men and 300 mg for women. US values are a bit higher: 400-420 mg for men and 310-320 mg for women. That is the total from all sources: food, water and supplements.

Magnesium is in very ordinary foods. A diet built on white bread, processed meat and sweets has little of it, though.

Figures are rounded, based on USDA FoodData Central and NIH. The famous “magnesium banana” is actually modest, while a handful of pumpkin seeds as a snack beats many supplements.

Magnesium deficiency: who is at risk

The internet blames low magnesium for everything: eye twitching, headaches, fatigue, anxiety, chocolate cravings. As a pharmacist, I’ll be direct: these symptoms are nonspecific. Poor sleep, stress and a dozen other things cause them too.

Blood tests are tricky as well. Serum magnesium reflects a tiny share of your stores, and the body keeps blood levels steady for as long as it can by pulling magnesium from bone. So a normal result does not rule out a mild deficiency, while a low one definitely needs a doctor’s attention.

The real risk groups are these. People taking omeprazole, pantoprazole or other proton pump inhibitors for more than a year, since these drugs can lower magnesium. People on loop or thiazide diuretics. People with type 2 diabetes, who lose magnesium in urine. Regular drinkers. People with chronic diarrhea, Crohn’s disease or celiac disease. And older adults, who both eat less and absorb less.

Which magnesium is best: the forms explained

Magnesium in supplements always comes as a salt, paired with some acid. That pairing decides how much magnesium you actually get, how well it is absorbed and how your gut reacts.

Magnesium oxide. The cheapest and most “concentrated”: about 60% of its weight is magnesium. But it dissolves poorly, and in a study by Firoz and Graber only a few percent of the dose was absorbed. It draws water into the bowel, so it is often used as a gentle laxative for constipation. If your gut is sensitive and prone to bloating, oxide may not be the best choice.

Magnesium citrate. Dissolves well and is absorbed noticeably better than oxide, as shown among others in a randomized trial by Walker and colleagues in 2003. A good all-round option at a fair price. In large doses it can loosen stools too, though less than oxide.

Magnesium bisglycinate (glycinate). Magnesium bound to the amino acid glycine. Very gentle on the stomach and bowel, so people who get diarrhea from other forms like it. A lot is written about its effect on sleep, but direct human studies of this particular form are still scarce.

Lactate and malate. Well absorbed and well tolerated. Lactate often appears in pharmacy combinations with B6.

L-threonate. The trendy “brain” form. Evidence that it reaches the brain better comes mostly from animal studies. It contains little magnesium, about 7-8%, and costs a lot. In Ukraine it was approved for dietary supplements, together with magnesium citrate malate, by the same amendments in Order No. 203, which we covered separately.

Chloride and sulfate. Chloride absorbs well but tastes bitter and often loosens stools. Sulfate (Epsom salt) taken by mouth is mainly a laxative, and Epsom salt baths are pleasant, but there is no evidence they top up magnesium through the skin.

Percentages are approximate and depend on how much water a given salt contains.

The main trap: how much magnesium is really in a tablet

Even careful shoppers get confused here. “Magnesium citrate 500 mg” does not mean 500 mg of magnesium. Such a tablet holds roughly 55-80 mg of magnesium itself, the rest is citric acid.

So look for “elemental magnesium” or the nutrition table that lists magnesium in mg per daily serving and as a percentage of the reference intake. In the EU and Ukraine the reference value used on labels for magnesium is 375 mg.

And compare prices per 100 mg of elemental magnesium. A “cheap” bottle often turns out more expensive once you realize the dose takes four tablets.

How to take magnesium properly

Dose. For general support, 100-300 mg of elemental magnesium a day from a supplement is usually enough, especially if you eat nuts, seeds and whole grains. European experts set a safe upper limit of 250 mg a day for supplemental magnesium, US experts 350 mg. Above these doses the risk of diarrhea rises sharply.

Timing. Take it with or after food for a calmer stomach. Evening suits most people. If the dose is 300 mg or more, split it in two: better absorption and a happier gut.

Duration. Any effect on muscles or wellbeing usually shows after a few weeks. A common approach is 1-2 months, then a break to see whether it made a difference. If it did not, the problem may not be magnesium.

Medicines to space it from. Magnesium binds some antibiotics in the gut. Take tetracyclines and fluoroquinolones (ciprofloxacin, levofloxacin) at least 2 hours before or 4-6 hours after magnesium. Keep bisphosphonates for bones (alendronate) at least 2 hours apart. Levothyroxine for the thyroid is also best taken separately, a few hours apart.

Who should ask a doctor first. People with chronic kidney disease, because the kidneys struggle to clear excess magnesium and it can build up. Also people with myasthenia gravis, serious heart rhythm disorders, or those already taking magnesium-containing antacids or laxatives.

Magnesium for sleep, cramps and stress: what is proven

Sleep. A 2021 systematic review by Mah and Pitre pooled three small trials in older adults with insomnia. Magnesium shortened the time to fall asleep by about 17 minutes on average, but the authors rated the evidence as low quality. It may help a little, but the effect is modest.

Cramps. A 2020 Cochrane review concluded that magnesium is unlikely to help older adults with ordinary night leg cramps. Results in pregnancy are conflicting. For exercise-related cramps there is almost no data.

Stress and anxiety. A 2017 review found some signs of benefit in anxiety-prone people, but the studies were small and varied. In a 2018 trial by Pouteau and colleagues, magnesium with B6 did slightly better than magnesium alone in adults with severe stress and low magnesium.

Blood pressure. A meta-analysis of 34 trials found that about 370 mg of magnesium a day for three months lowered blood pressure by about 2 mmHg on average. A small but real effect, especially in people low in magnesium.

What is a label actually allowed to claim? In the EU, approved claims for magnesium include “contributes to a reduction of tiredness and fatigue”, “contributes to normal functioning of the nervous system” and “contributes to normal muscle function”. Promises like “cures insomnia” or “stops cramps” go beyond the rules for food supplements.

Frequently asked questions

Conclusions

Adults need 300-350 mg of magnesium a day. Start with your plate: buckwheat, oats, beans, nuts, seeds, greens and a piece of dark chocolate go a long way.

If you need a supplement, citrate, bisglycinate, lactate or malate suit most people. Oxide is absorbed less and fits people with constipation. Check the elemental magnesium per daily serving and stay within 100-300 mg a day from supplements.

Take magnesium with food, split larger doses, and space it from antibiotics and bisphosphonates. If you have kidney disease, see your doctor first.

About the Author

Kateryna Braitenko is a Ukrainian journalist and author specializing in writing articles for pharmaceutical publications. She holds a philology degree from Donetsk National University and a pharmaceutical degree from the National Pharmaceutical University in Kharkiv. She lives in Kyiv and continues her career, covering relevant issues in medicine and pharmaceuticals.