Magnesium: What It Does, How Much You Need, Deficiency Symptoms and Best Food Sources

First of all: this is general information, not personal advice. If you suspect you are low in magnesium, have kidney disease or take medication, your doctor is the one who should assess it. That said, magnesium is one of the easiest minerals to cover with food, as long as you know where to find it.

How much magnesium you need per day

EFSA reviewed its reference values in 2015 and, because there were not enough data to calculate an average requirement, it set an adequate intake based on what healthy populations in the EU consume: 350 mg a day for adult men and 300 mg for adult women. For boys aged 10 to 17 it is 300 mg and for girls, 250 mg. Be careful not to confuse two different figures: the adequate intake refers to everything you eat, while the upper limit of 250 mg a day refers only to magnesium from supplements, water or fortified foods, not to the magnesium in ordinary food.

Foods high in magnesium: milligrams per serving

How to read it: seeds and cocoa are the most concentrated sources, but they are eaten in small amounts; leafy greens and legumes provide a lot because they are eaten in large portions. Bananas, which often appear on these lists, provide little: 32 mg per fruit. With the servings in the table, a handful of nuts, a plate of legumes or vegetables and a whole grain add up to about 190-340 mg: a good part of the 300-350 mg set by EFSA, or all of it. If you want to know the calories in these servings, check the food calorie table.

Symptoms of low magnesium: why they cannot be used for self-diagnosis

In true deficiency, neuromuscular symptoms predominate: cramps, spasms, tremors, weakness and tiredness, often together with changes in calcium and potassium. But cramps and tiredness have dozens of causes, from exertion to lack of sleep, so on their own they do not show that you lack magnesium. Hypomagnesaemia is diagnosed with a blood test (it is usually defined as serum magnesium below 0.7 mmol/L), and because less than 1% of the body's magnesium is in the blood, a normal result does not always rule it out: interpreting that is the doctor's job. If cramps often wake you up, also look at potassium and mention it at your appointment.

Magnesium supplements: forms and EFSA's limit

If your doctor recommends a supplement, the form matters. In Walker's trial (2003), with 300 mg a day for 60 days, citrate and amino-acid chelate were absorbed better than magnesium oxide, which did not differ from placebo. The upper limit adopted by EFSA (set by its Scientific Committee in 2001) is 250 mg a day of added magnesium for adults, including pregnant women, and children from 4 years of age. It is based on the most sensitive effect: mild diarrhoea, which appears in a small share of adults from about 360 mg a day of magnesium from salts like those in supplements. Magnesium from food does not count towards that limit, because it has not been shown to cause diarrhoea. This is not a recommended dose, only the safety ceiling.

• Magnesium sulphate (Epsom salt) is used as a laxative: it is not the form intended to cover your needs.
• Spreading the intake over the day improves digestive tolerance, according to the same report.
• With kidney disease, the kidneys clear magnesium less well: do not take supplements without medical advice.
• It can reduce the absorption of some medicines (certain antibiotics, for example): ask your pharmacist how to space them out.

Sleep and cramps: what the evidence says

Cramps: the 2020 Cochrane review pooled 11 trials with 735 people. For night-time cramps with no obvious cause, mostly in people over 60, magnesium did not differ from placebo (0.18 fewer cramps per week, a non-significant difference), and the authors conclude it is unlikely to provide noticeable prevention; in pregnancy the results are contradictory, and there are no trials in exercise-related cramps. In addition, between 11% and 37% of those who took it had digestive complaints, mainly diarrhoea (compared with 10-14% on placebo). Sleep: the meta-analysis by Mah and Pitre (2021), with only 3 trials and 151 older adults, found they fell asleep about 17 minutes sooner, with no significant improvement in total sleep time and low or very low quality evidence; the review by Arab (2023) found an association in observational studies and contradictory results in trials. In athletes without deficiency, a meta-analysis of 14 trials (Wang, 2017) found no strength improvements either. Bottom line: the effect, if it exists, is small, and seems to concentrate in people who start from a deficiency.

Magnesium is a good example of how the solution usually lies on the plate, not in a bottle: a handful of nuts, a plate of legumes or vegetables and whole grains cover the 300-350 mg set by EFSA. Log your meals with Renzy to see whether those sources really show up in your week, and leave supplements for when a professional sees a reason.