What is magnesium?

In one line

Magnesium is an essential mineral that helps many chemical reactions in the body so that muscles, nerves and bones work properly.

What is magnesium?
A mineral you often see in the supplement aisle
You often see 'magnesium' in the supplement aisle and on workout supplement labels. This post explains what kind of mineral magnesium is, where it is in the body, what it does, and how it appears in food and supplements.
In one line
A mineral that muscles, nerves and bones need
Magnesium is a mineral people must get from food. It is used to keep muscles and nerves working properly, the heart beating steadily, and bones strong.
What a mineral is
Elements the body needs
Minerals are elements the body needs, such as calcium, magnesium, iron and zinc. The body uses minerals to keep the bones, muscles, heart and brain working properly. Magnesium is one of the minerals needed in larger amounts, along with calcium, sodium and potassium.
Where it is in the body
Over half in bone, very little in blood
An adult body contains about 24 g of magnesium. A little over half is in bone, and most of the rest is in muscle and other body tissues. Less than 1% of the body's total is in the blood.
Job (1) Helping enzymes
Used in more than 300 chemical reactions
Proteins that help chemical reactions in the body are called 'enzymes'. Magnesium is needed for more than 300 enzyme reactions. These include the reactions that get energy from food and that build proteins.
Job (2) Muscles and nerves
Used when muscles tighten and relax
Muscles tighten when they get a calcium signal and relax only when that calcium is cleared away. Magnesium helps clear the calcium so muscles can relax. Magnesium is also used for nerves to pass signals and for the heart to beat steadily.
Where it is found
Dark green vegetables, nuts, beans
Most magnesium in food comes from dark green leafy vegetables. Magnesium also sits at the center of chlorophyll, the substance that makes leaves green. Nuts such as almonds, beans and tofu, and whole grains such as brown rice are also rich in it.
How much a day
310 to 420 mg a day for adults
The recommended amount for adults is 310 to 420 mg a day, depending on age and sex. 'Absorption' means digested nutrients passing from the gut into the blood; only part of the magnesium you eat is absorbed and the rest leaves in stool. The kidneys send extra magnesium out in urine to keep the blood level steady.
Supplements and excess
Also used as a laxative
Magnesium in supplements comes joined to other substances, as in magnesium oxide or magnesium citrate. Some of these have long been used as laxatives or to calm stomach acid. Problems from too much magnesium are rare and mostly happen in people whose kidneys work very poorly.
A common misconception
Is all supplement magnesium the same?
No. Given the same amount of magnesium, magnesium citrate raised blood and urine magnesium more than magnesium oxide. This means more of it was absorbed into the body. In a study lasting two months, magnesium oxide showed no difference from a dummy pill in blood and urine magnesium.
Summary
A mineral that helps chemical reactions in the body
Magnesium is a mineral that helps many enzyme reactions so that muscles, nerves and bones work properly. In supplements, magnesium citrate was absorbed more than magnesium oxide. Related words: mineral, enzyme, calcium.