BACKGROUND:For most people, muscle cramps are an occasional problem. For others, they are so frequent and painful, they can be disabling. Cramps occur when a muscle involuntarily goes into an intense contraction. They usually last seconds or minutes, but the pain and tenderness can persist for hours. Calf and foot muscles cramp most commonly, and are especially problematic during the night.
Apart from muscle cramps associated with exercise, which tend to be relatively short-lasting, chronic cramping occurs more frequently among the elderly, during the second half of pregnancy, and with certain medical conditions and pharmaceuticals. Chronic cramping can be due to a serious underlying condition and should always be evaluated medically. However, many cases occur without a clear cause and are referred to as idiopathic muscle cramps.
Various treatments are recommended for cramps, including drinking water, stretching the muscles, massage and medications. For seriously painful, chronic cramps, quinine has been used, although it was not officially approved for that. Quinine is extracted from the bark of the cinchona tree and is better known for treating malaria and giving tonic water its bitter taste.
In 2006 the US Food Drug Administration recommended against using quinine for cramps because of a lack of evidence of benefit and concerns about its side effects. While adverse effects are infrequent, they can be very serious. This led to renewed interest in other supplements for cramps, with magnesium frequently recommended.
EVIDENCE FROM STUDIES
Magnesium is a very important electrolyte in the body, known to be involved with more than 300 enzyme systems. Regular intake of magnesium is important, with high-fibre foods being a good source. However, as modern diets have contained less fibre, magnesium intake has dropped, with deficiency more common among the elderly.
Very few studies have tested magnesium for muscle cramps. The Cochrane Collaboration publishes systematic reviews of the evidence regarding the effectiveness of many interventions. The Health Research Board provides funding to make their library available for free from any internet connection in Ireland (TheCochraneLibrary.com).
They published a review of magnesium for muscle cramps during pregnancy. The strongest evidence of benefit was for magnesium, though the benefit was modest. Two-thirds of the women continued to get muscle cramps, but at a reduced frequency and intensity. The reviewers noted that as of 2010, five additional studies were in various stages of publication. When those results are available, the review’s conclusions might need to be changed.
In other people with idiopathic muscle cramps, the results are not encouraging. Another systematic review published in 2010 found only two studies investigating the topic. They both found magnesium no better than placebo for older adults with frequent leg cramps of unknown origin.
PROBLEMATIC ASPECTS
Adverse effects are uncommon with magnesium. Some people have gastrointestinal problems, with occasional diarrhoea. Large doses can cause electrolyte imbalances leading to dizziness and heart problems.
RECOMMENDATIONS
Because of magnesium’s many roles in the body, adequate intake is important. Foods that are high in fibre tend to contain magnesium also. These include whole grains, green vegetables, legumes, seeds and nuts. Hard water also has a high magnesium content.
Muscle cramps are painful and disturbing. If they occur frequently, it is important to have their cause investigated. For those with idiopathic muscle cramps, except during pregnancy, the evidence is not strong regarding magnesium. However, given that it is inexpensive, important for the body and safe, taking magnesium supplements for a trial period might be worth it. Studies have used 250-300mg per day. However, the evidence suggests that stretching and massage are the best options available.
Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University.
