How much magnesium do you need per day?

The RDA for magnesium is 400–420 mg a day for adult men and 310–320 mg for adult women, depending on age.

These are the reference amounts used on US food labels and in dietary guidance, not personal targets. What you need shifts with age, pregnancy, medication and health conditions. The % Daily Value shown on every food page here is calculated against the FDA Daily Value for magnesium, which is 420 mg a day.

What this means for you

Magnesium is the nutrient people are most often told they fall short of, and at first glance the survey data agrees. An analysis of national survey data found that 48 per cent of Americans take in less than the estimated average requirement. Before you act on that, it is worth knowing where the requirement itself came from, because that part is less settled than the 48 per cent makes it sound.

The reason is structural rather than mysterious. Magnesium sits in the parts of plants that processing takes out, the bran of a grain, the germ, the skin of a seed. Refine the flour and most of it goes. So the foods that carry real amounts are exactly the ones a convenience diet leaves out.

One change that works

A handful of seeds or nuts most days, and wholemeal instead of white wherever you do not mind the swap. A cup of roasted pumpkin seeds is 649 mg, which is more than a day and a half, though a cup is a lot of seeds. Sesame, sunflower and Brazil nuts are all in the same range. This is a nutrient you fix with a habit, not with a single meal.

Established. The wholemeal half of that gives back less than it looks. Add phytic acid to bread at the level found in wholemeal and magnesium absorption falls from 32.5 per cent to 13.0. At the level found in brown bread it falls to 24.0. Wholemeal still carries far more magnesium than white flour does, and a much smaller share of it reaches you. Worth doing, and thinner than the swap sounds.

Two sources sit outside the food table altogether. If your water is hard, some of your magnesium arrives from the tap. Across ten studies, people whose drinking water carried more magnesium died of coronary heart disease about 11 per cent less often. Nine of those ten were European and seven looked backwards rather than forwards, so read it as a reason to stop counting tap water as nothing.

The second is how you drink it. Twelve men took the same 126 mg of magnesium from mineral water, either in seven small servings across the day or in two large ones. Spread out, they absorbed 50.7 per cent of it. In two goes, 32.4.

Where 400 milligrams came from

The target is 400 to 420 mg a day for men and 310 to 320 for women. It rests on balance studies: people live on weighed food for weeks while everything leaving the body is collected, and the intake where losses and intake meet is taken as the requirement. Somebody has now pooled every one of those studies run at the US Department of Agriculture laboratory in Grand Forks, 150 women averaging 51 years and 93 men averaging 28, on controlled diets of at least 28 days. Balance came out neutral at 165 mg a day, with a prediction interval from 113 to 237.

Unsettled. That is well under half the figure on the label, and it comes from the same kind of experiment the label was built on. The researchers who ran those metabolic wards read the same data and put the average requirement near 175 mg a day and the recommended intake near 250 mg for a 70 kg adult. Nobody has settled the disagreement. What it means for you is that the benchmark you are told you fall below is itself under argument, so read 48 per cent of the country being short as a statement about a number rather than about 48 per cent of people being unwell.

Unsettled. The label number has the same trouble from the other end. The 420 mg is built to cover 97 to 98 people in every hundred, and the agency that sets it says plainly that it is usually not the best estimate of any one person's requirement, because nobody knows what that is. Below the Daily Value and short of magnesium are two separate findings, and the Daily Value was never placed where the shortfall begins.

The floor is real all the same. Postmenopausal women living in a metabolic unit on a Western diet that supplied 107 mg of magnesium a day went into negative balance, and the way their bodies handled calcium shifted with it. Adding 220 mg a day turned both around. So there is a level too low to live on, and it sits a long way under 400.

The heart data points the same direction. Across 16 prospective cohorts, the link between dietary magnesium and fatal ischaemic heart disease flattened out above roughly 250 mg a day. Past that point, eating more did not buy anything measurable.

Established. The safe upper limit for magnesium applies only to supplements and medicines. Magnesium in food and drink is not capped, and you are not going to overdo it from seeds.

Myth. Magnesium is sold for blood pressure, blood sugar, sleep and cramps, and the shelf promises more than the trials deliver. Supplements lower blood pressure only marginally. The American Diabetes Association says there is not enough evidence for routine use in diabetes. The migraine data comes from a handful of small, short trials, three of four of which found a modest effect at up to 600 mg a day. On cramps there is now a clearer answer: a Cochrane review of five trials in 307 older adults with night cramps found the number of cramps a week moved by 0.18 against placebo. The strong case for magnesium is about food rather than tablets.

Not for everyone. High doses from supplements commonly cause diarrhoea with nausea and cramping, and the effect arrives fast. If your kidneys are impaired the picture changes completely, because the body can no longer clear the excess, and supplements then need medical supervision.

The early signs of genuine deficiency are loss of appetite, nausea, fatigue and weakness. They are so general that they are useless for working out what is wrong with you on your own. A persistent version of them is a reason to see someone, not a reason to buy magnesium.

Two results are worth knowing before you decide whether a supplement is for you. For sleep, the entire randomised evidence is three trials in 151 older adults, who fell asleep about 17 minutes sooner than on placebo, on evidence the reviewers rated low to very low. For blood pressure, 38 trials in 2,709 people found a drop of 2.81 mmHg overall and 7.68 mmHg in people already on blood pressure medicine, with nothing at all in people whose pressure was normal. The full review is here.

Two long-term medicines are worth knowing about here, because they change the answer for the people taking them. Loop and thiazide diuretics increase magnesium losses in urine and can deplete it, and prescription proton pump inhibitors taken for more than about a year can drive blood magnesium below normal. Neither is a reason to stop a drug. Both are a reason to mention magnesium at the next review.

One more claim now has trial evidence behind it, and it comes with its own caveat. Across seven randomised trials in 325 adults with a diagnosed depressive disorder, magnesium lowered depression scores, with a standardised difference of 0.92. The authors of that review say plainly that the trials are too small to turn the result into clinical advice. Read it as a reason to take the shortfall seriously rather than as a treatment.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Foods highest in magnesium on this site

• Pumpkin and squash seed kernels, roasted — 649 mg per 1 cup (155% DV)
• Sesame seed kernels, dried — 517.5 mg per 1 cup (123% DV)
• Sesame seeds, whole, dried — 505.4 mg per 1 cup (120% DV)
• Brazil nuts, dried, unblanched — 500.1 mg per 1 cup, whole (119% DV)
• Sunflower seed kernels, dry roasted — 454.7 mg per 1.0 cup (108% DV)

All magnesium sources ranked →

Full guide: Magnesium: widely under-eaten, and widely over-promised