Magnesium is a useful nutrient to understand because the reason people fall short of it is structural rather than personal. It is the atom at the centre of the chlorophyll molecule, which means it arrives in a diet attached to green leaves, seeds, beans and intact whole grains. Refining a grain removes the germ and the bran, and most of the magnesium leaves with them. A diet built on refined starch is low in magnesium almost by construction, whatever else is done to it.
Analyses of United States national dietary survey data put roughly half of adults below the estimated average requirement [2]. That is not an exotic deficiency state. It is an ordinary gap in an ordinary diet.
The foods, by what a portion actually delivers
| Food | Typical portion | Magnesium | Per 100 g | Share of a day |
|---|---|---|---|---|
| Pumpkin seeds | 1 oz (28 g) | 166 mg | 592 mg | 52% |
| Spinach, cooked | 1 cup (180 g) | 157 mg | 87 mg | 49% |
| Swiss chard | 1 cup, chopped (175 g) | 151 mg | 86 mg | 47% |
| Sunflower seeds | 1 cup, with hulls, edible yield (46 g) | 150 mg | 325 mg | 47% |
| Tempeh | 1 cup (166 g) | 134 mg | 81 mg | 42% |
| Black beans | 1 cup (185 g) | 120 mg | 65 mg | 38% |
| Quinoa | 1 cup (185 g) | 118 mg | 64 mg | 37% |
| Brazil nuts | 1 oz (6 kernels) (28 g) | 105 mg | 376 mg | 33% |
| Edamame | 1 cup (160 g) | 99.2 mg | 62 mg | 31% |
| Chia seeds | 1 oz (28 g) | 93.8 mg | 335 mg | 29% |
| Pinto beans | 1 cup (185 g) | 85.1 mg | 46 mg | 27% |
| Chickpeas | 1 cup (185 g) | 83.3 mg | 45 mg | 26% |
Ranked by the amount in a portion someone would actually eat, not per 100 g — ranking per 100 g puts seeds and dried herbs on top and tells you very little about a plate. Amounts are USDA FoodData Central values per 100 g converted to the portion shown. “Share of a day” is against the 320 mg reference intake for a woman aged 31-50, which is the higher bar for most of these; a man's target appears in the table below.
Every amount above is a laboratory-analysed USDA FoodData Central value per 100 g, converted to the portion shown [5] — the same figures the site's nutrient tools calculate against, so this page and those tools cannot disagree.
Two things are worth noticing in that table. The first is how quickly it adds up: three or four of those portions across a day covers an adult requirement without any single heroic food. The second is that the list is almost entirely plants, and that is not an editorial preference — it follows from where magnesium is. Nuts, seeds, legumes, leafy greens and whole grains are simply where the mineral lives.
Want this checked against a day you actually ate rather than a list? What nutrients am I missing? takes one day of food and reports which nutrients it covered and which fell short, magnesium among them, against the reference intakes for your own age and sex.
How much you need
| Age | Women | Men |
|---|---|---|
| 9-13 | 240 mg | 240 mg |
| 14-18 | 360 mg | 410 mg |
| 19-30 | 310 mg | 400 mg |
| 31-50 | 320 mg | 420 mg |
| 51-70 | 320 mg | 420 mg |
| 70+ | 320 mg | 420 mg |
NIH Dietary Reference Intakes, the same figures the site's nutrient tools use. Pregnancy and breastfeeding raise several of these; the nutrient gap tool applies the right set for you.
Note what the table does not do: the requirement does not fall with age. It rises through adolescence, settles, and stays there. Meanwhile appetite tends to shrink, medication lists tend to grow, and absorption declines modestly — which is why shortfall becomes more likely in later life without anybody changing what they eat.
Why a normal blood test does not settle it
This is the part that surprises people, including some clinicians. Less than one per cent of the body's magnesium is circulating in blood; the rest is in bone and inside cells. The body defends the circulating number hard, pulling magnesium out of bone to hold serum steady. A normal serum magnesium is therefore entirely compatible with depleted stores [1].
That is not an argument for ignoring the test — a low serum magnesium is meaningful and needs attention. It is an argument against treating a normal one as an all-clear. For most people, what they habitually eat is the more informative question, and it is one they can answer themselves.
Who tends to run short
Beyond the general dietary pattern, a few groups are more likely to be genuinely depleted, and it is worth knowing whether you are one of them:
- Long-term proton pump inhibitor users. The FDA issued a safety communication in 2011 after cases of low magnesium in people taking PPIs for a year or more [3]. If you have been on omeprazole or similar for years, this is worth raising.
- People on loop or thiazide diuretics, which increase urinary magnesium loss.
- People with type 2 diabetes, where higher glucose loads drive magnesium out in the urine.
- People with Crohn's disease, coeliac disease or chronic diarrhoea, where absorption is the limiting step rather than intake.
- People who drink heavily, through a combination of poor intake, urinary loss and impaired absorption.
Food first, and why the supplement number is lower than you expect
The 350 mg upper limit applies to supplements, not to food. The tolerable upper intake level for supplemental magnesium in adults is 350 mg a day — lower than the 420 mg daily requirement, which reads like a contradiction until you notice they are measuring different things [4]. There is no upper limit on magnesium from food, because the kidney handles dietary magnesium without difficulty in anyone with normal renal function. The limit exists because magnesium salts taken as a pill draw water into the bowel; the commonest consequence of exceeding it is diarrhoea. If you have reduced kidney function, magnesium supplements are a decision for your own doctor, not a shelf.
So the practical answer is unglamorous. A handful of pumpkin seeds, beans in something twice a week, greens most days and grains kept intact will move this number further than a bottle will, and will bring the potassium, fibre and folate that travel with it.
Related, and free: top foods by nutrient ranks the whole USDA database for six nutrients with your own daily values, and the calorie and nutrient counter looks up any single food.
Questions people actually ask about this
Which foods are highest in magnesium?
By a portion someone would actually eat: pumpkin seeds, cooked spinach, Swiss chard, sunflower seeds, tempeh, black beans and quinoa all deliver roughly 120 to 165 mg — between a third and a half of a day in one serving. Ranked per 100 g instead, seeds and dried herbs dominate and the answer stops being useful, because nobody eats 100 g of pumpkin seeds.
How much magnesium do I need a day?
The NIH Dietary Reference Intake is 420 mg a day for men aged 31 and over and 320 mg for women, having risen from 400 and 310 mg in the 19 to 30 band. Requirements do not fall with age, which is part of why shortfall is common in older adults.
Why is magnesium so often low in modern diets?
Magnesium sits at the centre of the chlorophyll molecule, so it arrives with green leaves, seeds, beans and whole grains. Refining a grain strips the germ and bran where most of it lives, and a diet built on refined starch is therefore low in magnesium almost by construction. Analyses of US national dietary survey data find roughly half of adults taking in less than the estimated average requirement.
Can a blood test tell me if I am low in magnesium?
Not reliably. Less than one per cent of the body's magnesium is in the blood, and the body defends that number by pulling magnesium out of bone and cells. A normal serum magnesium is therefore compatible with genuinely depleted stores, which is why what you habitually eat is the more informative question.
Should I take a magnesium supplement?
Food first, for a specific reason: the tolerable upper intake level of 350 mg a day applies to supplemental magnesium only, not to magnesium from food, and the commonest side effect of exceeding it is diarrhoea. If you take a proton pump inhibitor long term, a loop or thiazide diuretic, or you have type 2 diabetes or a malabsorption condition, that is a conversation to have with your own doctor rather than a decision to make in a supplement aisle.
Does cooking destroy magnesium?
Magnesium is a mineral, so it cannot be destroyed by heat, but it does leach into cooking water. Boiling vegetables and discarding the water loses some; steaming, roasting, or using the liquid in a soup or stew keeps it. Cooked spinach appears high on this list partly because cooking collapses the volume, so a cup holds far more leaf than a raw cup does.