Magnesium is an essential metallic macro-element that in the earth is found only in the form of its compounds, the most abundant of which is dolomite, a mixture of magnesium and calcium carbonates.
It is an essential component of bones and teeth, contributing to their structural stability by forming cross-linkages with calcium phosphate.
Magnesium is available only from the diet, although some is present in drinking water. Hard water contains significant quantities of the mineral, as do some types of bottled mineral waters.
Magnesium is very widely distributed and is present in all foods. The richest sources are:
- soya beans
- all types of nuts
- dried brewer’s yeast
- wholemeal flour
- brown rice
- dried peas and other pulses
Other good sources include seafood, bananas, dried fruits, meats and all vegetables. Cereals and vegetables represent the main sources of magnesium in the average diet, providing more than two thirds of the daily intake.
Refining and processing of cereals and flour cause serious losses of magnesium, so it is important to eat wholegrain cereals wherever possible.
Chlorophyll contains 2.7% of magnesium but is not a significant source of the mineral as fresh greens contain only 0.1% chlorophyll. Hence, one pound of greens supplies a total amount of 95 mg magnesium, but of this only 12 mg is in the form of chlorophyll.
The nervous system, the muscles and the heart can all be affected by magnesium deficiency. Typical nerve problems include irritability of the central nervous system, disorientation, convulsions and psychotic behaviour (delusions, hallucinations). Nervousness and anxiety usually precede the more serious manifestations of deficiency.
Muscle problems are induced by abnormal nerve muscle functions leading to weakness, vertigo, muscle cramps and tremors, shaky movements and unsteady gait. There is often twitching of the facial muscles and rapid involuntary movements of the eyes up and down or side to side. Tetany is common and is characterised by ‘pins and needles’ of the lips, tongue, fingers and feet, with muscular spasms of the hands and feet as well as the facial muscles.
Low levels of magnesium in the blood can result in a rapid heartbeat. Irregular heartbeats and palpitations may also suggest a lack of magnesium.
Deficiency can also induce a greater susceptibility to the toxic effects of the heart drug digitalis. In all these symptoms, low blood levels of magnesium should be tested to confirm deficiency.
Poor diets, i.e. those with an excess of highly refined and processed foods, malnutrition, loss of appetite and anorexia nervosa can all reduce magnesium intake and lead to low body levels.
High dietary intakes of raw bran, phosphates and saturated fats can inhibit absorption of magnesium.
Reduced or impaired absorption may also be caused by malabsorption conditions, by chronic diarrhoea induced by laxative abuse or by short-term diarrhoea in children, particularly in those with protein-calorie malnutrition.
Alcoholism is a frequent cause of a reduction in body magnesium stores, mainly because of increased urinary excretion and decreased dietary intakes. Regular vomiting episodes and diarrhoea induced by alcoholic drinks can result in magnesium deficiency. The mental problems associated with alcoholism have also been attributed in part to magnesium deficiency.
Excessive losses of magnesium in the faeces or urine are a result of many diseases including gastro-intestinal problems and some kidney complaints.
Magnesium is essential for the efficient utilisation of vitamins Bl and B6.
Magnesium deficiency may be associated with potassium deficiency. It may be necessary to correct the former in order to treat the latter.
The ratio of magnesium to calcium in the diet should be between 1:1 and 1:2.
Magnesium carbonate is insoluble in water but dissolves in gastric juices to produce magnesium chloride and carbon dioxide. In the intestine, magnesium carbonate, like all magnesium salts, acts as a saline laxative because it is more soluble at intestinal pH level than calcium carbonate.
Any magnesium absorbed is usually rapidly excreted in the urine.
Magnesium carbonate has antacid properties but is effective only at intakes above 1 g. It is also a laxative but this property is only apparent at high potency intakes of 5 g or more. Hence at the recommended intake of three dolomite tablets per day, the total amount of magnesium is only 155 mg. This is far below any potency likely to have a laxative effect or to contribute to any significant antacid action, although the magnesium dissolved (as magnesium chloride) will be absorbed to some extent and will thus help overcome any mild dietary deficiency of the mineral.
The only potential side effect of excessive magnesium intake is hypermagnesamia, in which blood serum levels are elevated. However, this condition only affects individuals with renal failure who ingest large quantities of magnesium salts. The problem is caused not by increased absorption of the mineral, but by an inability to excrete it.
Magnesium carbonate is an approved food additive, serial number 504, with no limits set on the amount that can be added to foodstuffs.