Magnesium is a key mineral in our body and needed for more than 300 different chemical reactions. It is also essential for muscle contractions and nerve transmission while also keeping your heart beating steadily and your immune system strong. In this article, I’ll outline the key functions of magnesium as well as cover the different health conditions where magnesium is thought to play a role such as heart disease and high blood pressure, diabetes, muscle cramping and poor sleep quality. And then I’ll look at the main food sources of magnesium and critique the merits of the many different supplemental forms of magnesium.
Magnesium is an essential dietary mineral, and the second-most common electrolyte in the human body. You have about 30 grams of magnesium in your body of which half is found in the bones. Much of the rest of the body’s store of magnesium is found in the muscles and soft tissues, with only 1 percent in the extracellular fluid where it serves as an electrolyte. As an electrolyte, it serves to maintain fluid balance.
Magnesium is also a cofactor for hundreds of enzymes. Magnesium is involved in many physiologic pathways including energy production, nucleic acid and protein synthesis, and cell signalling. Together with calcium, magnesium is also involved in muscle contraction and blood clotting.
Magnesium is critical to heart function and seems to protect against high blood pressure and heart disease, mostly around how it can reduce blood pressure and assist in reducing arterial stiffness. Interestingly, people living in areas with hard water, which contains high concentrations of calcium and magnesium, tend to have lower rates of heart disease so this indicates a role for this mineral here.
Regarding a benefit for magnesium on lowering blood pressure, it is mostly seen when either a person is low in magnesium levels in the body to start with, or if they already have an elevated blood pressure.
Magnesium supplementation has also been linked to a benefit on glucose metabolism, especially in people with diabetes. Magnesium may be helping with improved insulin functioning so this could explain the link. The benefit though is small and seems to mostly occur in people who are on the verge of developing type 2 diabetes or already have problems with glucose metabolism.
Sleep quality is another area that comes up when discussions turn to magnesium supplementation. While magnesium is very commonly recommended for helping with sleep quality, the research base is small but appears to show a small benefit when taken by people who report bad sleep quality. Its role here may be as a sedative-like agent.
Because magnesium is an electrolyte and has a key role in muscle contraction, a deficiency is thought to have some relationship to muscle cramping. The evidence here though is from observations of a higher rate of muscle cramping coinciding with lower serum magnesium levels which is seen in pregnant women and people experiencing night cramps in the calf muscle.
Another piece in the puzzle is that very low serum magnesium levels are associated with severe muscle cramping and muscle pain. A broad Cochrane review and meta-analysis in a wide range of patient groups found that magnesium was not able to reduce the risk of cramps. There were though no randomised controlled trials evaluating magnesium for exercise‐associated muscle cramps so it is unclear if supplementation would help athletes who are frequent crampers.
Magnesium deficiency in otherwise healthy people eating a balanced diet is rare. The kidney has an extraordinary ability to reduce magnesium loss in the urine, and thus achieve magnesium balance on a wide variety of levels of consumption in the diet.
While there are many food sources of magnesium, there is no one food source that stands out so even the best sources tend to only meet about one-fifth of needs. Since magnesium is part of chlorophyll (the green pigment in plants) then green leafy vegetables are useful sources of magnesium with spinach being one of the best sources. Wholegrains and nuts such as almonds also have good amounts of magnesium in them. Meats and milk have an intermediate content of magnesium, while refined foods generally have the lowest.
Even with an adequate diet, some people are at increased risk of magnesium deficiency, including people with digestive disorders, such as celiac disease and chronic diarrhoea.
In the short term, getting too little magnesium does not produce obvious symptoms. Low magnesium intakes for a long time, however, can lead to magnesium deficiency. Also, some medical conditions and medications interfere with the body’s ability to absorb magnesium or increase the amount of magnesium that the body excretes, which can also lead to magnesium deficiency.
Symptoms of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. Extreme magnesium deficiency can cause numbness, tingling, muscle cramps, seizures, and an abnormal heart rhythm.
Choosing a magnesium supplement
Magnesium supplements are sometimes marketed as magical elixirs that can fix a long list of health problems such as muscle tension and cramps, low energy levels, and insomnia. But as I outlined earlier, the evidence to support many of these claims in otherwise healthy people isn’t that strong.
Deficiency of magnesium though is not unknown so because a dietary deficiency can be common, magnesium supplements are popular. And there are many different formulations to choose from with the standard dose for magnesium supplementation in the range of 200 to 400 milligrams per day. Magnesium as a supplement is bound to other molecules, typically salts, known as chelations. This is to stabilise the magnesium and prevent cross-reaction with other minerals.
Magnesium supplements are available as magnesium oxide, magnesium malate, magnesium gluconate, magnesium chloride, magnesium citrate salts, as well as several amino acid chelates like magnesium aspartate. Gastrointestinal side-effects, like diarrhoea and bloating, are more common with magnesium oxide or magnesium chloride due to the lower absorption rates of these two forms and is why magnesium oxide tends to be used as a laxative. Magnesium chloride is easily absorbed orally and used to treat heartburn, constipation, and low magnesium levels.
In general, magnesium citrate is a good choice for supplementation and is the most commonly used form of magnesium due to its high water solubility and bioavailability at around 25 to 30 percent.
Another gentle form for those sensitive to magnesium oxide or magnesium citrate is magnesium malate. It is often recommended for people suffering from fatigue and symptoms of fibromyalgia, but no current scientific evidence supports this. Magnesium bound to amino acids such as aspartate show good levels of bioavailability but tend to be lesser than magnesium citrate.
Magnesium L-threonate is another supplemental form of magnesium and is the salt formed from mixing magnesium and threonic acid, a water-soluble substance derived from the metabolic breakdown of vitamin C. This supplement has begun to be investigated for specifically increasing brain magnesium levels. Some emerging research on its cognitive effects suggesting that supplementation may be of benefit in people with Alzheimer’s disease, but it is still early days.