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Magnesium: Everything you need to know

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Magnesium is one of our body's most important minerals, but what does it do and could you be deficient?

Why do you need magnesium?

Magnesium helps to power the 'pumps' that control movement of salt in and out of cells, making it essential for muscle contraction, nerve conduction and triggering a regular heartbeat, as well as healthy bones and energy production.

Magnesium's numerous roles in the body include:

  • reducing tiredness and fatigue
  • contributing to electrolyte balance
  • contributing to normal energy-yielding metabolism
  • contributing to normal muscle function
  • contributing to normal psychological function
  • contributing to the maintenance of normal bones
  • contributing to the maintenance of normal teeth
  • playing a role in the process of cell division

Half of our body's total magnesium is stored within bones and half is found inside our cells.1 Very little (0.3 per cent) is found in blood fluid (serum) which makes it difficult to assess magnesium status because laboratories measure magnesium levels found inside red blood cells.

Magnesium is stored in our skeleton, which means it helps to maintain strong bones. Researchers have found that women with osteoporosis have significantly lower magnesium levels than similar women without osteoporosis.2

In the UK-based EPIC-Norfolk study, both men and women with the lowest magnesium intakes were found to have a greater risk of hip fracture compared to those with the highest intakes.3

Taking magnesium supplements for two years has also been shown to help prevent osteoporosis by increasing bone mineral density and reducing the risk of bone fractures.4

Magnesium-rich foods

Magnesium is found in nutrient-dense wholefoods such as nuts and seeds (especially pumpkin seeds, Brazil nuts, almonds and cashews), dark green leaves such as spinach, beans (especially soy and lentils), fish (especially mackerel), dried fruit (especially figs) and wholegrains such as quinoa, millet, Bulgur wheat and brown rice.

Once these sources are processed, however, much of their magnesium is stripped out, and so white flour and rice contain less magnesium than brown. Magnesium absorption from food is further decreased by excess dietary fat, alcohol, salt, phosphoric acid (found in canned fizzy drinks) and coffee.5

Drinking water can provide useful amounts of magnesium in hard water areas and – some good news - dark chocolate is also an excellent source.

Magnesium deficiency

The EU-recommended daily intake for adults is 375mg magnesium per day, but few people seem to achieve this. Average intakes within the UK are around 323mg for males and 228mg for females.6

According to the National Diet and Nutrition Surveys, almost one in eight adults aged 19-46 (13 per cent) obtain less than the lower reference nutrient intake (LRNI) for magnesium, putting them at risk of deficiency symptoms. This rises to one in four (25 per cent) of adults aged 75 and over.

Poor intakes of magnesium can cause a wide range of troublesome symptoms including weakness, nausea and fatigue. If you are experiencing any of these, it's worth increasing your magnesium intake. If symptoms continue or become worse, however, do seek medical advice.

Should I be supplementing?

Diet should always come first, but if you are cutting back on food to lose weight, or simply can't eat as much as you used to, then magnesium supplements are available.

There are several different types of supplement, of which the most popular and cost-effective is magnesium oxide. Although this form is less easily absorbed than some other magnesium salts, this is more than compensated for by the high amount of magnesium it provides - 600mg per 1g of magnesium oxide.

Although magnesium citrate is better absorbed, it only supplies 113mg of magnesium per gram because the citrate part is relatively heavy. Similarly, magnesium gluconate only supplies 58mg of magnesium per gram, which explains why it is often described as gentler and less likely to have a laxative effect. Some supplements contain a blend of different magnesium salts for maximum absorption.

In reality, the body is clever at absorbing what it needs, and if you are deficient the amount of magnesium you absorb will increase, whichever magnesium salt you take.

Magnesium is often combined with calcium and vitamin D in bone health supplements, or combined with B vitamins in supplements designed to help boost energy production and reduce fatigue.

How much should I take?

Most magnesium supplements supply the recommended dose of 375mg. Higher amounts can have a laxative effect.

An EU safety review of magnesium concluded that doses of up to 400mg magnesium per day would not be expected to cause side effects.

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