This mineral makes up a whopping 0.05 percent of your body weight. Seventy percent is located in the bones with calcium and phosphorus, the rest in soft tissues and body fluids.

Magnesium is essential for all the major processes of the body. It's needed for normal heart and lung function. The small amount present in the body helps to release energy from food, to build new cells and proteins, and has a major role in enabling muscles to relax, including those in the walls of arteries, where it may help to prevent raised blood pressure. Without magnesium, calcium can't work effectively. High blood pressure and weak hearts are improved by intravenous magnesium.

Availability in food

Natural food sources of magnesium are almonds and other nuts, raw wheat germ, soy, milk, whole grains, seafood, figs, com, apples, and seeds.

Magnesium can be found in vegetables, but the amount they contain depends on the amount of magnesium in the soil. In recent years, magnesium has been lost from the soil through acid rain and the application of chemical fertilizers. It is present in most nuts, seeds and whole grains, but up to 85 per cent can be lost from whole grains when they are milled. When foods are boiled, magnesium leaches into the water; this can be retrieved if you use the water in gravy or soup.

What if your intake is too low?

Magnesium deficiency causes fatigue, loss of appetite, insomnia, apathy and poor memory. Lack of magnesium can cause painful periods in women and spasm of the muscles in tile walls of tile arteries, which may raise blood pressure. It may also contribute to incontinence in the elderly and bed-wetting in children.

When extra may be needed

  • If you live in a soft-water area or drink bottled water that has a low mineral content
  • If your diet consists mostly of processed foods, or contains excessive protein, fat, sugar, caffeine, salt or fizzy drinks
  • If you regularly consume moderate or large amounts of alcohol
  • If you have heavy or painful periods, or are prone to pre-menstrual symptoms
  • If you are at risk of osteoporosis (take only under medical supervision)
  • During pregnancy and when breast feeding
  • When taking the birth-control pill regularly, diuretics (water pills), antacid preparations (for indigestion) or receiving hormone replacement therapy
  • If losses of magnesium from the body are high: such as in urine when taking diuretics (water tablets), in faeces if you have diarrhoea or pass loose stools, or in sweat if you perspire excessively from heat or exercise
  • If you regularly take large amounts of vitamin C daily (more than 1,OOOmg)

Can too much be toxic?

Magnesium overload is virtually unknown because any excess is rapidly eliminated from the kidneys and in the faeces. However, toxicity can occur if calcium levels are low, especially if magnesium supplements are given by injection. Symptoms include muscle weakness and fatigue.

Using a supplement

Calcium and magnesium should normally be taken together and the amount absorbed depends on the form in which they are taken. Dolomite and bonemeal contain both minerals and appear to be fairly well absorbed, but there have been concerns about contamination from lead and other toxic metals and it is best to choose a preparation that is specified as being contaminant-free.

Of the chemical preparations, calcium is probably absorbed best when taken as the aspartate or citrate salts, and magnesium as the gluconate salt, or when chelated with amino acids.

Magnesium oxide and sulphate are also useful preparations.

As the body's absorption of calcium and magnesium can be altered by food, supplements with a little vitamin C may be most efficiently taken between meals or at bedtime, when they may also enhance sleep. Preparations that include hydrochloric acid and vitah1in D are well absorbed by the body. Daily dosage: 300-500 mg, in the form of magnesium citrate, glycinate, or gluconate.

If you have muscle cramps, angina, or osteoporosis, I recommend you take up to 800 mg per day, 400 in the morning and 400 before bed.