What does magnesium do in the body?

What does magnesium do?

Magnesium is a working part of more than 300 enzymes, the proteins that run the body’s chemistry. Among other things it is needed to:

• release energy from food (the body’s energy molecule, ATP, is active only when bound to magnesium)
• make proteins and copy DNA
• carry nerve signals and let muscles relax after they contract
• keep a steady heart rhythm
• build bone and help the parathyroid glands, which control calcium, work normally
• help insulin move sugar into cells

The NHS summarises it as helping turn food into energy and keeping the parathyroid glands, which produce hormones important for bone health, working normally.

Where does the body keep it?

An adult holds about 25 g of magnesium. Between half and 60% is in bone, and most of the rest is inside the cells of muscles and soft tissues. Less than 1% is in the blood. The body keeps blood levels in a narrow range by drawing on bone and by adjusting how much the kidneys let go, which is why an ordinary blood test can look normal even when stores are low.

How much do you need?

In the UK, the reference intake is 300 mg a day for men and 270 mg for women aged 19 to 64. Other bodies set higher figures: the European Food Safety Authority says 350 mg for men and 300 mg for women. See how much magnesium you need for every age group, and the safe upper limit for supplements.

Who is most likely to run short?

• Older adults, who absorb less from food and lose more through the kidneys.
• People with type 2 diabetes, because high blood sugar increases losses in urine.
• People who drink heavily.
• People with conditions that affect the gut, such as Crohn’s disease or coeliac disease, or who have had bowel surgery.
• People taking proton pump inhibitors (such as omeprazole) for a long time, or loop and thiazide diuretics.
• People who eat few wholegrains, nuts, seeds, beans and green vegetables.

Food or supplements?

Food first. The richest sources are seeds, nuts, beans, wholegrains, dark leafy greens and, more modestly, dark chocolate. See foods high in magnesium. Supplements are useful when your diet falls short, when you are in one of the groups above, or for specific uses with some evidence, such as migraine prevention or constipation.

If you do take one, the form changes how much magnesium is in each capsule, and the dose matters more than the brand.