Mineral
Magnesium
It is needed for more than three hundred enzyme reactions, most of it is stored in bone where a blood test cannot see it, and roughly half of adults in the US take in less than the recommended amount. Here is where to find it.
What it does
Magnesium is a cofactor: it does not do the work itself, it is the thing several hundred enzymes need in order to do theirs. That includes the enzymes that build protein, the ones that copy DNA, and the ones that turn food into usable energy — which is why a shortage shows up as vague tiredness rather than as anything specific.
It also sits opposite calcium at the muscle. Calcium signals a muscle fibre to contract; magnesium is part of what lets it release again. The same pairing runs in nerve tissue and in the walls of blood vessels.
About 60% of the magnesium in an adult body is in bone, most of the rest inside cells, and less than 1% in blood. That last number matters more than it sounds: a normal blood magnesium result does not rule out low stores, because the body will pull magnesium out of bone to keep blood levels steady.
How much you need
| Who | Per day | Note |
|---|---|---|
| Infants, 0–6 months | 30 mg | Adequate Intake, from milk |
| Infants, 7–12 months | 75 mg | Adequate Intake |
| Children, 1–3 years | 80 mg | — |
| Children, 4–8 years | 130 mg | — |
| Children, 9–13 years | 240 mg | — |
| Men, 19–30 | 400 mg | — |
| Men, 31 and over | 420 mg | — |
| Women, 19–30 | 310 mg | — |
| Women, 31 and over | 320 mg | — |
| Pregnancy | 350–400 mg | Depending on age |
These are Recommended Dietary Allowances, except where marked: for infants there is not enough evidence to set one, so an Adequate Intake is given instead. The percentages in the table below are of the 420 mg Daily Value used on food labels, which is a single number for everyone over four and therefore generous for most people reading it.
From our own data
The foods highest in magnesium
Magnesium sits in chlorophyll, so green leaves carry it — but seeds, nuts and beans carry far more per bite, because they are storing minerals for a plant that has not grown yet.
- 1
Hemp seeds, hulled167% · DV - 2
Pumpkin seeds131% · DV - 3
Soy flour, full-fat102% · DV - 4
Brazil nuts90% · DV - 5
Flax seeds89% · DV - 6
Garden cress seed88% · DV - 7
Tahini85% · DV - 8
White sesame seeds84% · DV - 9
Poppy seeds83% · DV - 10
Chia seeds80% · DV - 11
Unsweetened baking chocolate78% · DV - 12
Wheat germ76% · DV
Per 100 g, from our copy of USDA FoodData Central, against a Daily Value of 420mg. Ranked by amount, not by how much of it your body actually takes up — read the next section before you act on the order.
The table above is per 100 g. The app weighs the portion you actually ate.
What helps, and what gets in the way
Helps
- Eating it across the day rather than in one go — absorption falls as the dose rises
- Whole grains over refined ones: milling removes the germ and bran, where the magnesium is
- Soaking or sprouting beans and grains, which breaks down some of the phytate
Gets in the way
- Very high supplemental zinc, which competes for absorption
- Phytates in unsoaked whole grains and legumes, which bind magnesium in the gut
- Chronic alcohol use and some diuretics, which increase how much is lost in urine
Absorption from food runs at roughly 30–40% and rises when stores are low, which is the body doing the sensible thing. Supplemental magnesium oxide is poorly absorbed compared with citrate or glycinate; if a clinician has recommended a supplement, the form is worth asking about.
Who tends to fall short
Groups where intake or absorption is commonly lower than the reference. It is a list of populations, not a list of symptoms — it cannot tell you anything about yourself.
- People eating mostly refined grains, since milling removes about 80% of the magnesium
- Older adults, who absorb less and excrete more
- People with type 2 diabetes, coeliac disease or Crohn’s, through losses or malabsorption
- Long-term users of proton pump inhibitors, which can lower magnesium over years
Cook it
Pumpkin seed and spinach purée
From 8 months, and it scales up for the rest of the table
Ingredients
- 2 tbsp pumpkin seeds, unsalted
- 2 large handfuls of spinach, washed
- 1 small potato, peeled and cubed
- 1 tsp olive oil
- 3–4 tbsp warm water, breast milk or formula, to loosen
Method
- 1Toast the seedsDry pan, medium heat, three to four minutes, moving them constantly. They are done when they smell nutty and one or two start to pop. Let them cool completely — warm seeds turn to paste rather than powder.
- 2Grind themTo a fine powder in a spice grinder or a small blender. For a baby this is not optional: whole seeds are a choking hazard until well past the second birthday.
- 3Cook the potatoSimmer in unsalted water for 12–15 minutes, until a knife goes through easily.
- 4Wilt the spinachAdd it to the pan for the last 60 seconds. Longer than that and most of the folate ends up in the water rather than in the meal.
- 5BlendDrain, keeping a little of the cooking water. Blend the potato and spinach with the olive oil, then stir in the ground seeds. Loosen to the texture your baby is used to.
Introduce seeds the way you would any other new food: on their own first, in the morning, and not alongside anything else new. Speak to your health visitor or paediatrician before starting, particularly if there is a family history of allergy.
Sources
- NIH Office of Dietary Supplements — Magnesium
- Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride
- USDA FoodData Central
This page is education, not medical advice. It does not diagnose anything and it is not a substitute for a clinician who knows your history. If you think you are short of magnesium, the answer is a blood test and a conversation, not a supplement bought on the strength of an article.
Every food above, and 12,601 more, with the full panel — in the app.