NOW Foods Magnesium

Magnesium oxide· evidence: Moderate

Magnesium oxide is the cheapest and most concentrated form of magnesium: about 60% of its weight is magnesium, so a small tablet can carry a large dose. It does raise magnesium intake, but in small studies a smaller share of it is absorbed than from organic forms such as citrate or glycinate, and more of it stays in the gut, where it draws in water.

That makes oxide a reasonable budget choice if you simply want to top up intake and your stomach tolerates it. If you have found other magnesium upsets your stomach, oxide is usually the worst option. There is no good evidence that any form is better for sleep, stress or cramp, and these are not authorised claims.

Typical dose: Usually 200–400 mg of elemental magnesium a day (NRV 375 mg).

Safety: Oxide is the form most likely to cause loose stools or diarrhoea, and it is used as a laxative at higher doses. EFSA sets an upper level of 250 mg a day of magnesium from supplements; the FSA advises up to 400 mg a day is unlikely to cause harm. Take a few hours apart from tetracycline or quinolone antibiotics and bisphosphonates. Speak to your GP first if you have kidney disease.

Research we looked at:
Firoz M, Graber M (2001). Bioavailability of US commercial magnesium preparations. Magnes Res 14(4):257–262.
Walker AF et al. (2003). Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res 16(3):183–191.
EFSA Scientific Committee on Food (2001). Opinion on the tolerable upper intake level of magnesium.

Magnesium· evidence: Moderate

Magnesium is an essential mineral found in green vegetables, nuts, seeds, wholegrains and beans. UK surveys show that some groups, particularly teenagers and some adults, eat less than the recommended amount. A supplement reliably raises intake, and people with a low intake or a diagnosed deficiency are the ones most likely to notice a difference. Most people eating a varied diet get enough from food.

Labels often show the weight of the whole compound (for example 1,000 mg of magnesium citrate), but only part of that is magnesium itself. What matters is the elemental magnesium per daily dose, compared with the NRV of 375 mg. Organic forms such as citrate, glycinate (bisglycinate), malate and taurate are generally absorbed a little better than oxide in small studies, but differences between them are modest and no form has been shown to be better for any particular use.

Magnesium is widely sold for sleep, stress and cramp. These are not authorised claims. Reviews have found the evidence for sleep is of low quality, and a Cochrane review found magnesium is unlikely to prevent ordinary muscle cramps in older adults.

Typical dose: Most supplements give 100–400 mg of elemental magnesium a day (NRV 375 mg). The NHS says adults need about 270–300 mg a day in total, mostly from food.

Safety: High doses loosen stools or cause diarrhoea, especially citrate and oxide. EFSA sets an upper level of 250 mg a day of magnesium from supplements, and the FSA advises that up to 400 mg a day from supplements is unlikely to cause harm. Magnesium can reduce absorption of some antibiotics (tetracyclines, quinolones) and osteoporosis drugs (bisphosphonates), so take them a few hours apart. Speak to your GP first if you have kidney disease.

Research we looked at:
NHS. Vitamins and minerals: others – magnesium. nhs.uk.
EFSA NDA Panel (2015). Scientific opinion on dietary reference values for magnesium. EFSA Journal 13(7):4186.
Expert Group on Vitamins and Minerals (2003). Safe upper levels for vitamins and minerals. Food Standards Agency.
Garrison SR et al. (2020). Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev 9:CD009402.

Cost per daily dose lets you compare packs of different sizes fairly.Worked out from our current prices.