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Dietitians say there is not enough consistent, strong evidence that magnesium supplements improve sleep, digestion, muscle recovery, cramps or anxiety, while high doses can cause serious harm.
There is not enough consistent, strong evidence to show a cause and effect relationship between magnesium supplementation and better sleep, dietitians say. The same lack of firm evidence applies to claims about digestion, muscle recovery, cramps and anxiety.
Scarlett Johansson magnesium use raises questions
The question has gained attention partly because actress Scarlett Johansson has spoken about taking magnesium. Dietitian Shine said the general sentiment was, If she takes magnesium and says it works for her, then maybe I should be taking it too. Magnesium is an essential mineral the body needs for blood pressure regulation, bone health and many other important functions. The body does not produce it, so diet is critical.
Good sources include nuts, seeds, legumes, leafy greens and brown rice. Magnesium deficiency is not common in Australia. It is more likely in people with certain conditions such as diabetes or bowel disease. Despite this, magnesium is promoted widely as a supplement anybody can take for a range of conditions.
On sleep, Shine said some studies have reported improvements in certain aspects of sleep when taking magnesium supplements, but the findings are inconsistent. Studies are generally small, short-term and use different forms and doses of magnesium, which makes it difficult to draw firm conclusions about whether supplementation reliably improves sleep, she said. Sports dietitian Dr Evangeline Mantzioris said another difficulty is that studies measure sleep quality differently.
Some examine sleep duration, some the time taken to fall asleep, and some the depth of sleep. But there are not enough consistent, strong findings to show strong cause and effect, she said. If someone was struggling with sleep, we would want to look at sleep hygiene first, such as lights and devices off, and no caffeine, Mantzioris said. Stress and other factors should also be considered.
Magnesium laxative effect and exercise risks
On digestion and gut health, Shine said some forms of supplemental magnesium draw water into the intestine, and this has a laxative effect. The British Dietetic Association names magnesium oxide as an example. Mantzioris said people who exercise regularly need to be careful, because taken wrongly, magnesium can cause nausea, abdominal cramping and diarrhoea. Intense exercise jolts the intestines while diverting blood away from them, making the gut extra sensitive to magnesium and giving a laxative double-whammy effect.
We always say in sports that you do not want to take magnesium when you know you are going to be out training the next day, she said. On exercise recovery, magnesium is important for metabolism and muscle contraction, Shine said. But its role in these processes does not mean that supplementation will improve recovery, including from muscle pain and damage.
Magnesium is classified as a Group C supplement, a category where the scientific evidence does not support a benefit among athletes or is insufficient to draw firm conclusions, she said. There is no good evidence that magnesium supplementation prevents muscle cramps, Mantzioris said. While soaking in a warm magnesium salt bath may bring relief, it is more likely the warm water that helps rather than the magnesium itself, according to the dietitians.
Marketing exploits anxiety and nervous system role
On nerves and anxiety, Shine said marketing of magnesium products exploits it being essential to calming the nervous system. The marketing suggests supplementation is also essential to preventing and treating stress and anxiety. Magnesium is involved in processes including nerve transmission and regulation of neuronal activity, helping nerves communicate throughout the body, she said.
However, there is no strong evidence that magnesium supplementation provides broad benefits for nervous-system function. Mantzioris said supplement companies play on people's real-life stressors. They capture our fear that we might be deficient in something, and try to sell that this might explain why we are stressed or tired, she said. People with concerns can see a doctor.
High magnesium doses pose serious toxicity risks
Taking magnesium in the absence of a known deficiency has some risks, Shine said. Very high doses can cause toxicity, including low blood pressure, breathing problems, abnormal heart rhythms and, in severe cases, cardiac arrest, she said. The Guardian is asking readers what health trend they want examined. People aged 18 or over can share their story, anonymously if they wish, through the Guardian's encrypted form, and only the Guardian has access to the contributions.
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