Tatevosian Yana/ShutterstockMagnesium has become one of the most popular supplements on the market. People take it for a whole host of reasons, ranging from better sleep to reducing stress, preventing muscle cramps, boosting energy levels and preventing deficiencies. Social media has made it even more popular, meaning many people now take it in search of a simple, straightforward way to feel better. Magnesium does have real physiological effects, but these are often confused with clinical benefits that have not been firmly established in healthy people.So, what does the science say?No substitute for dietMagnesium is an essential mineral. It is involved in hundreds of enzymatic reactions, and we need it for energy metabolism, muscle and nerve function, protein synthesis, bone maintenance and electrolyte balance. Not getting enough may be linked to fatigue, weakness or neuromuscular disorders. However, this does not mean everybody needs to take it as a supplement. When there is a deficiency of any kind – whether vitamins or minerals – supplements have clear benefits. But the effects are much less evident when a person’s diet already provides enough.The best dietary sources of magnesium are whole grains, leafy green vegetables, pulses, nuts, seeds and pure cocoa. For many people, incorporating more of these foods into their diet makes more sense than taking a capsule. A supplement alone does not improve a poor diet, and trusting a pill to make up for what we do not get from food often amounts to self-deception. But there is potentially a lot of money to be made in persuading people that this is not the case.Accordingly, the European Union has set certain authorised health claims that can be made about magnesium. These include that it helps reduce tiredness, supports normal energy metabolism, and contributes to normal muscle and nerve function. While these claims are true in a physiological sense, they do not mean that a magnesium supplement acts as a universal energiser or relaxant. They simply indicate that the body needs this mineral to function properly. Leer más: Should I take a magnesium supplement? Will it help me sleep or prevent muscle cramps? Different types of magnesiumThe idea has also caught on that each problem requires a specific form of magnesium: citrate for constipation, bisglycinate for sleep, malate for tiredness, and threonate for the brain.It is true that different minerals vary in terms of how well they are absorbed and tolerated by the digestive system, but proving that a particular type is clinically superior for promoting sleep or reducing stress in healthy people is another matter entirely. This idea is based more on marketing strategy than scientific conclusion.Science provides a more nuanced view of each of these claims. Sleep is one of the most widely touted benefits, and magnesium’s role in neuromuscular excitability and in relaxation processes gives it a plausible biological basis.Nevertheless, clinical evidence is limited. A recent clinical trial of magnesium bisglycinate in adults with poor sleep quality suggests only a modest reduction in the time taken to fall asleep. We need further clinical studies – with larger sample sizes and objective measures of sleep – before we can definitively say that magnesium improves sleep quality. To date, the European Union has not approved any health claims linking this mineral to improved sleep.The story is similar with muscle cramps. The available reviews do not show a clear benefit for people who experience them regularly. The idea that “magnesium eliminates cramps” is far too simplistic. As far as energy is concerned, the body is not a reservoir that can be filled indefinitely. If its needs are already met, taking more magnesium will not produce any more energy. The benefit of magnesium supplements is to correct a deficiency, not to turn a mineral into a stimulant. Leer más: Can supplements keep your brain sharp? Why the evidence is more complicated than it seems Marketing vs scienceThe minerals we get from food rarely cause problems, but high-dose supplements can cause diarrhoea, nausea and abdominal pain.The risk is higher in people with kidney disease or those taking certain medicines. Furthermore, magnesium may interfere with some antibiotics and medicines for osteoporosis if taken at the same time.Taken together, this invites a broader reflection. For healthy people that follow a complete, balanced diet, most food supplements are unnecessary. Some may be useful in specific situations – such as diagnosed deficiencies, greater need or clinical indications – but this does not justify their widespread use.The problem is not just the product, but also the message that goes with it. The idea that a capsule can make up for a lack of sleep, chronic stress or unhealthy habits is very appealing from a commercial point of view, but it is driven more by market interests than by genuine public health needs.The bottom line is this: magnesium is an essential nutrient with very important functions, and it is not a baseless fad. But when considering taking supplements, we should not ask ourselves “which supplement am I missing?” We should be asking “do I actually need it, or have I just been persuaded to buy it?”. The best advice is, perhaps, the least appealing. Dietary sources come first, and supplements should only be used when needed, properly prescribed by a healthcare professional. A weekly e-mail in English featuring expertise from scholars and researchers. It provides an introduction to the diversity of research coming out of the continent and considers some of the key issues facing European countries. Get the newsletter!Maria Izquierdo-Pulido receives funding from the Spanish Ministry of Science, Innovation and Universities.Isabella Parilli Moser receives funding from the Spanish Ministry of Science, Innovation and Universities.Maria Fernanda Zeron Rugerio receives funding from the Spanish Ministry of Science, Innovation and Universities.