Dietary magnesium

Magnesium is an abundant mineral in the body and a cofactor in more than 300 enzyme systems, among them those for protein synthesis, muscle and nerve function, blood glucose control and blood pressure regulation. It is naturally present in many foods, added to others, sold as a dietary supplement and contained in some medicines such as antacids and laxatives.

In the body

An adult body contains about 25 g of magnesium, 50% to 60% of it in the bones and most of the rest in soft tissues; less than 1% is in blood serum, where its level is kept under tight control. The kidneys largely control the body's magnesium balance.

Food and supplements

Good sources are green leafy vegetables, legumes, nuts, seeds and whole grains, and magnesium is also added to some breakfast cereals and other foods. About 30% to 40% of the magnesium in food and drinks is absorbed.

Supplements contain magnesium in many forms, such as oxide, citrate and chloride, and their labels state the amount of elemental magnesium, not the weight of the whole compound. The forms that dissolve well in liquid are absorbed better: the aspartate, citrate, lactate and chloride forms tend to have higher bioavailability than magnesium oxide and magnesium sulfate.

How much

In the United States, the recommended intakes for adults range from 310 to 420 mg a day, depending on age, sex and life stage.

Too little

Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue and weakness; as it worsens, numbness, tingling, muscle cramps, seizures and abnormal heart rhythms can occur. Gastrointestinal diseases such as Crohn's disease and coeliac disease, type 2 diabetes, chronic alcoholism and some medicines can lead to deficiency.

Too much

Magnesium from food is not a risk for healthy people, because the kidneys remove the excess. High doses from supplements or medicines can cause diarrhoea, nausea and abdominal cramps; the tolerable upper intake level for supplemental magnesium is 350 mg a day for adults. Very high doses can cause magnesium toxicity with low blood pressure, vomiting, difficulty breathing and irregular heartbeat.

Magnesium may interact with some medicines, such as oral bisphosphonates and tetracycline and quinolone antibiotics, and some medicines, such as diuretics and proton pump inhibitors, can affect magnesium status.

Products containing it

• All Day Fit A-Z Compact tablets (S 06)
• Fito 40 capsules (S 07)
• Magnesium capsules (D 246)