Magnesium is a mineral found in many foods including include nuts and seeds (especially pumpkin seeds, Brazil nuts, almonds and cashews), dark green, leafy vegetables (especially spinach and Swiss chard), beans (especially soy, lentils and white beans), fish (especially mackerel), dried fruit (especially figs) and wholegrains (especially quinoa, millet, Bulgur wheat and brown rice).
Dark chocolate and tap water in hard-water areas are also important sources for some people.
Magnesium is needed for over 300 enzymes to work properly in the body, making it essential for every metabolic process from the production of energy to the synthesis of protein and genetic material. It is needed for muscle contraction, nerve conduction, and to maintain your heart rhythm and blood pressure. You even need magnesium for the action of sex hormones, and for the production of brain chemicals to maintain normal mood and quality sleep.
Lack of magnesium is common and may contribute to insomnia, fatigue, weakness, muscle trembling or cramps, numbness and tingling, loss of appetite, poor co-ordination, palpitations, hyperactivity, low blood sugar – and a raised blood pressure.
Magnesium relaxes smooth muscle cells in artery linings to reduce arterial spasm, which may explain why researchers have found that people with the highest dietary intakes of magnesium (an average 454mg/day) were a third less likely to die from any medical cause over a 5 year follow-up period, than those with the lowest intakes (average 318mg per day). And a large analysis of data from 19 studies involving almost 533,000 people found that the risk of cardiovascular events (heart attack, stroke) was 15% lower in those with the highest dietary magnesium intake and 33% lower in those with the highest blood levels of magnesium.
Magnesium infusions are used to treat high blood pressure in some situations, such as pregnancy. Analysis of data from 22 trials, involving 1173 people found that taking magnesium supplements (average dose 410mg) reduced systolic blood pressure (upper reading) by 3mmHg to 4 mmHg and diastolic blood pressure (lower reading) by 2mmHg to 3mmHg.
Low magnesium intake is common
Unfortunately, processing strips out much of the magnesium from food sources such as grains. Average adult intakes in Europe and the US are therefore relatively low at around 323 mg for males and 228mg for females.
Low magnesium levels can cause spasm of coronary arteries (linked with angina or heart attack) and potentially dangerous abnormal heart rhythms. These effects seem to be more pronounced during times of stress. Among obese individuals with type 2 diabetes, heart rhythm abnormalities were twice as common in those with low magnesium levels.
Magnesium supplements can have a laxative effect
Magnesium sulphate is the main component of Epsom salts, which has been a popular laxative since Victorian times. Magnesium in high doses is also used medically to clear the bowel before procedures such as colonoscopy and surgery.
The UK Expert Group on Vitamins and Minerals carried out a risk assessment on magnesium in 2003. They reported that ‘A few studies reported mild and reversible diarrhoea in a small percentage of patients and healthy volunteers at levels of 384mg to 470mg per day, but these symptoms were not observed in the majority of studies using similar or higher doses. For guidance purposes only, 400mg/day supplemental magnesium would not be expected to result in any significant adverse effects.’
The average magnesium intake from food is around 280mg per day. Drinking water can also contain high levels of magnesium in some areas, and the maximum intake from food, plus supplements, plus water has been estimated at 1400mg per day. To put this into context, the dose prescribed medically to clear the bowel (in a preparation called Picolax) includes 3.5grams magnesium oxide (which is more than double the maximum estimated intake, and almost ten times higher than the EU RDA of 375mg.
Some people do seem to be more sensitive to the laxative effects of magnesium than others. If you decide to take magnesium supplements and experience this effect, cut back on the dose, take it every other day, or obtain magnesium topically by soaking in a bath containing Dead Sea or Epsom mineral salts, or using a magnesium-rich oil that is rubbed onto the skin.
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