Magnesium - smooth muscle relaxant

Magnesium is abundant on planet earth, comprising 1-2% of the soils and 0.1% of the seas. It is an essential element for most living things, with the exception of some insects. For us humans magnesium forms a vital part of the skeleton where 60% of our magnesium is found. This is also where we effectively store magnesium for use in other parts of our body. 

Magnesium is often found in compounds such as Epsom Salts (MgSO4), a traditional cure for constipation, Milk of Magnesia (Mg(OH)2), traditional cure for indigestion and dolomite MgCa(CO3)2.

Functions of magnesium.

Magnesium is a co-factor for more than 250 enzymes within our bodies. These are responsible for a number of functions:

  • Releasing energy from food. The energy in food is ultimately converted into ATP, adenosine triphosphate, which is always associated with a magnesium ion in its active form. No magnesium, no energy!
  • Creating new nucleic acids (RNA and DNA), that are needed for cell division and hence growth and repair of our bodies.
  • Creating new proteins as well as the synthesis of lipids and carbohydrates.
  • Synthesizing antioxidants, such as glutathione, that allow us to repair oxidative damage caused by toxins, radiation of excessive stress.
  • Helping other minerals such as calcium and potassium cross cell membranes. As such, magnesium can help our nervous system conduct impulses properly, leading to proper tone in our skeletal muscles and also in our smooth muscles such as those gut, urinary tract, blood vessels and uterus.

Basically magnesium is used extensively throughout our body and a lack of it, hypomagnesia, can cause lethargy, muscle spasms, nausea, depression and personality changes. It is also closely connected to our ability to retain calcium and potassium in our body and these minerals will also become depleted if we remain low on magnesium for a long period of time.

Conditions which may be helped by magnesium.

Magnesium is potentially helpful with a number of health conditions. Often these health conditions are associated with low levels of magnesium being present in the body. Even when serum magnesium is not low it is not always the case that magnesium levels are not depleted however as it is the levels of magnesium in the skeleton and in the cells where it is needed that are most crucial for health.

  • Asthma - Since magnesium is associated with relaxation of smooth muscle it is no surprise to find that people have looked to see if asthma symptoms could be improved by use of magnesium. One study on 55 adults, using 340mg of oral magnesium daily for 6.5 months led to improved quality of life1. Other objective measures of asthma control were also improved. Some studies have used intravenous magnesium for people with acute attacks2. The trial showed improvements lung function and rates of discharge from hospital. 
  • Cardiovascular conditions - Because magnesium helps with nervous conduction, and thereby muscle relaxation it has also been tested as a treatment both immediately after heart attacks and with people with furred up arteries. The result with magnesium therapy after heart attacks have been mixed, however there is good evidence linking increased intakes of magnesium, with reduced incidence of ischaemic stroke (the most common kind of stroke)3.
  • Chronic Fatigue Syndrome - This condition seems to benefit from magnesium supplementation4, with many sufferers recording low levels of magnesium in their red blood cells. 
  • Diabetes type II - There is a wealth of evidence that magnesium improves insulin sensitivity. It has also been found to reduce HbA1c, a marker of inability to handle blood sugar, and to reduce fasting glucose levls. All in all magnesium seems to be an effective supplement for those with type 2 diabetes. A 2003 trial, using magnesium chloride, found improvements in all three markers mentioned above5
  • Insomnia - There is good evidence that magnesium supplementation can help with the two conditions, restless legs syndrome and periodic limb movements in sleep6. This last condition being the one where you lash out and unintentionally hit your partner or vice versa. Other conditions that could keep us up at night, such as night cramps, and general restlessness, are also possible candidates for treatment with magnesium.
  • Irritable bladder - Using the same logic as those condition above, it is thought that bladder irritability could be caused not only by an enlarged prostate, but also by instability in the bladder itself, which is a sac of smooth muscle. In practice many people find magnesium to help with this condition. There is some evidence available also7.
  • Headache - The causes of headache are many and despite a splitting of the definition of headaches into three: cluster headache, tension headache and migraine, the three types are clearly related to one another and cannot be treated in isolation. Low magnesium levels have been associated with all three types of headache8 and as such magnesium is potentially a useful supplement. In practice many people that suffer with headaches although not all, seem to benefit from magnesium supplementation. Evidence is also availble from a number of studies9.
  • Oesophagal spasm - Another condition which may respond well to magnesium is oesophagal spasm, which can give rise to pain anywhere from below the breastbone, right up to the throat. Typically a hiatus hernia may be suspected, but in a number of cases, pain just below the breastbone will be due to oesophagal spasm. You may remember that milk of magnesia (Magnesium hydroxide) used to used as a tonic for indigestion. It is the effect of magnesium on the smooth muscle surrounding the gastrointestinal tract that underpinned its use in this context.

Magnesium in foods.

Some of the key foods that contain magnesium include nuts, fish and green leafy vegetables. All great foods to incorporate into your diet for many other reasons as well.


One of the most magnesium rich foods you can find, is the humble nut. Most nuts contain good amounts of magnesium. The amount of magnesium in 100g of nuts is as follows: almonds 275mg, brazils 375mg, cashews 292mg, hazels 160mg, macademia 130mg, pecans 121mg, pistachios 121mg and walnuts 158mg. So brazils are the winners followed by cashews. Given that the recommended daily amount is around 400mg, a good handful of nuts should give you a good dose of magnesium.


The amount of fish eaten by weight is normally greater than that of nuts, however nuts are still potentially a more potent source of magnesium. Nevertheless fish can make a useful contribution to magnesium intake. The amount of magnesium in 100g of fish is as follows: anchovies-canned 65mg, cod 31mg, haddock 50mg, herring (kipper) 41mg, mackerel 97mg, salmon 37mg, sardine-canned 39mg, tuna-canned 31mg, tuna-fresh 64mg. The winner here is the mackerel followed by the fresh tuna steak.

Green Leafy vegetables.

Magnesium is a key component of the machinery that allows plant leaves to photosynthesize, thereby producing energy for the plant. Any plant containing the photosynthetic pigment chlorophyll, will contain plenty of magnesium. The amount of magnesium in 100g of green leafy vegetables are as follows: chard 86mg, kale 57mg, parsley 50mg, seaweed-kelp 121mg, spinach 87mg. Kelp is a clear winner. This supernutrient food from the sea is rich in a large number of vitamins and minerals.

Many beans, such as soya and pinto beans are also a pretty good source of magnesium also. Bear in mind that the amount of magnesium you can absorb, will be affected by the type of food. For instance nuts, seeds and beans contain phytic acid that can bind to minerals such as magnesium in the gut and prevent their absorption. Phytic acid is broken down by an enzyme called phytase and soaking beans, seeds and even nuts can activate any phytase that is present in a food to bring the level of phytic acid down. Phytase can also be increased by consuming probiotic yoghurts. Fructo-Oligo saccharides (FOS) may also improve absorbability of magnesium10.

Supplementation and testing.

There are a range of different types of magnesium supplement provided by various companies. Some examples from companies I deal with are below:

  • Healthspan. 375g of magnesium oxide (magnesia) and magnesium hydroxide (milk of magnesia). Cost 90 for £6.75. (£2.00 for 10g).
  • Nutri. 100g of magnesium glycinate. Trade cost 120 for £11.05. (£9.21 for 10g). 
  • Biocare. 300g of magnesium phosphate and magnesium ethanolamine phosphate. Trade cost 90 for £12.98. (£4.81 for 10g).
  • Solgar. 200g of magnesium citrate. Cost 120 for £13 online. (£5.41 for 10g).

While magnesium supplementation is in general cheap, some companies produce magnesium more cheaply than others. However, it is worth considering how absorbable each type of supplement is as some such as magnesium oxide are unlikely to be absorbed from your intestines as well as magnesium glycinate, for instance.


It is worth being aware that magnesium supplements can have interactions with other minerals. For instance if you supplement zinc you could increase your need for magnesium, as zinc competes with magnesium for absorption from the gut. On the other hand, eating more protein actually seems to help with magnesium absorption.


Testing for magnesium status is an inexact science. It is thought that testing the amount in red blood cells gives a better idea of our magnesium levels than testing our serum (blood minus the red blood cells and clotting factors). Typical costs for two of the testing companies I deal with are:

  • Biolab - Trade price of £15 for a individual test for magnesium.
  • Genova - Trade price of £135 for a test of 8 important minerals including magnesium in red blood cells and 7 toxic heavy metals.

DrDobbin says.

Magnesium is a vital nutrient and a useful supplement for a number of conditions. It is generally safe and relatively cheap to supplement and as such is in my opinion worth a go if you suffer from some of the conditions mentioned above. Please seek professional advice when starting to supplement magnesium, it is always best to understand your supplements in the context of your overall health, your diet, any drugs and supplements you are taking, and your level and type of exercise regime.


1) Evidence that Mg can help with asthma.

2) Evidence that intravenous magnesium could help with acute asthma attacks.

3) Higher magnesium intakes associated with fewer strokes.

4) Good evidence that magnesium injections can help with Chronic Fatigue.

5) Evidence of positive effects for diabetics.

6) Reduction in unwanted movements during sleep with magnesium therapy.

7) Gordon D, et al. Placebo-controlled study of magnesium hydroxide for treatment of sensory urgency and detrusor instability:  Br J Obstet Gynaecol. 1998;105(6):667-9

8) Link between low magnesium and migraine.

9) Evidence for preventative effect of magnesium on migraine.

10) FOS helps with Mg absorption.