What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage |PART 1

By Myprotein Writer | Chris Tack

Clinical Specialist Physiotherapist 

Magnesium (Mg) is usually an abundant and always an important mineral in our bodies. It is required for more than 300 reactions in the body, involving metabolism, protein synthesis, cellular energy production, cell growth and DNA/ RNA development(1-2).

In this two part article series we will examine how magnesium can benefit not only our health, but also our sporting performance.


What does magnesium do?

Magnesium has a variety of functions which include maintain of the health of the body’s tissues (including nerve, muscle and bone); management of heart function (including the rhythm of our heart beat); our muscle tone; our blood pressure; our immune system; and our blood glucose levels (1-2).

What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage

However, these functions can only be sustained for as long as we sustain an appropriate concentration of Mg in our tissues. When we are unable to sustain this level is when issues occur.

Magnesium has been described as an “invisible deficiency”- predominantly because only a small percentage of magnesium is stored in our blood; and in order to know if you are deficient a blood test is taken. Therefore a blood test may come back as negative, and you may still have a deficiency of magnesium in either your muscles or your bones where it is more readily stored. Deficiency of Mg is actually not uncommon and therefore should not be ignored.


The Invisible Deficiency


Most magnesium intake deficits are marginal to moderate (e.g. 50%-90% recommended daily allowance is consumed)(3).

However, the spread of Mg deficiency is relatively wide. For example, deficiency has been observed in the young(4-5) and has links with the aging process(6). It has been seen in females more than males(4,7) but also has been identified in young men(8).

Deficiency has also been seen in varied sporting groups, including runners(9); ultra-endurance, adventure racers(10); and gymnasts(11). It has even been seen in varied team sports such as both football(12) and rugby(13).

Reasons for the wide spread of Magnesium deficiency

1) Modern food processing methods remove magnesium from our foods (e.g. refining grains)(14). Process foods such as vegetable oil, sugar, white flour and most things out of a box will be devoid of magnesium. Even industrial farming techniques will reduce the soil from which our food is grown of its magnesium.

2) Cooking processes (especially boiling) can remove magnesium.

3) Magnesium is not a compulsory requirement of our food labels for nutritional labelling.

4) Water treatment to soften water removes magnesium, meaning we do not sufficiently drink enough. Even bottled waters will be low on magnesium.

5) Other substances we consume can have effects to prevent magnesium absorption (e.g. phosphoric acid in carbonated soda will bind with Mg and prevent intestinal absorption) and calcium supplementation will block Mg absorption).

6) We lose too much of our bodies Mg through excretion in urine (particularly if you each too much sugar or salt, or drink too much tea/ coffee/ alcohol, or exercise intensely, or are stressed…)


Sources of Magnesium?


According to the US department of agriculture some specific foods have high amounts of magnesium, which include 1 ounce of almonds (80mg/ 20% of the dietary reference value) and half a cup of spinach (79mg/ 20% of DRV)(14).

Other sources could include peanut butter (49mg in 2 tablespoons), whole wheat bread (46mg in 2 slices), baked potato (43mg in 3.5 ounces), and brown rice (42mg in ½ cup).

Alternatively there are a variety of forms of supplementation, which include magnesium oxide, citrate, chloride, aspartate, lactate or sulphate(15-16). The important thing to consider when choosing is that aspartate, citrate, lactate and chloride are more readily absorbed and more “bioavailable” than both oxide and sulphate(18-22).

Additionally forms which can be dissolved in water are more easily and completely absorbed which increases the supplement’s efficiency(16-18).

nut butter

Magnesium | Health Benefits


As stated magnesium has variable and diverse functions in the body. However, when you are considering the specific benefits of Mg on health, the key function is its role in the prevention of inflammation secondary to oxidative stress.

A lot of research has been undertaken which can be summarised in the following sentences.

If you have a chronic inflammatory problem, it is likely you will be deficient in magnesium. However, being deficient in magnesium can also lead to said chronic issues.

Low levels of Mg are closely associated with chronic inflammation in the body(23-24), and subsequent pathological changes and development disease states. Such disease states can include atherosclerosis (where arteries harden and become blocked); hypertension (high blood pressure); osteoporosis (bone density loss); diabetes; cancer and stroke(18). We will discuss a few of these diseases further.

#1 Aging and Magnesium

What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage

The process of aging is often associated with Mg deficits. Usually during the process of getting older whilst plasma (blood) concentrations of Mg are sustained, the total amount of Mg in the body is reduced(25). Alternately, as we age secondary causes may reduce magnesium in the body (e.g. gastrointestinal issues may prevent absorption or there may be greater loss of Mg in urine).

However, we also know that oxygen-derived free radicals are produced at a greater rate in the elderly(25) and subsequently cause chronic inflammation states in the bodies tissues. From this state of increased and prolonged inflammation a variety of diseases can emerge.

#2 Cardiovascular Diseases and Magnesium

Mg supplementation has been seen to reduce C-reactive protein levels in older adults(26). C-reactive protein is a protein which is released into the blood by the liver as a reaction to tissue injury, infection or inflammation.

As such is has been identified as an indicator of cardiovascular disease risk(26).

Click the drop-downs to find out about the effects of Magnesium.


#3 Bone Density and Magnesium

A further physiological influence Mg has in the body which we shall discuss is its effect on bone formation.

Magnesium has an effect in modifying the activity of two different types of cells: osteoblasts (which assists bone formation) and osteoclasts (which assist bone absorption)(43). They also alter the concentration of other substances which influence bone formation- namely parathyroid hormones and vitamin D.

What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage

A reduction in Mg, therefore can lead to an imbalance between bone formation and bone loss. Positive relationships have been seen between the amount of Mg consumed and bone density in both men and women(44).

In those who suffer bone density diseases (such as osteoporosis), a reduced concentration of serum magnesium levels have been found compared to individuals with normal bone density(45). Thus supporting the fact that Mg deficiency is a potential risk factor for osteoporosis.

Consequently studies have examined the effectiveness of increasing Mg intake in these populations; and indicate that this may assist bone mineral density maintenance and increase in post menopausal and elderly women(46). Dosages of 290mg per day of Mg citrate for a period of 30 days has shown reduction in rate of bone turnover compared to placebo (suggesting a decrease in bone loss)(47).

Furthermore, a study in elite swimmers (a group where bone density issues have been seen due to the reduced amount of impact and loading through the skeleton) has shown both a reduction in bone density and Mg deficiency to the extent where Mg intake was described as an independent predictor of the degree of bone mineral density loss(48).

#4 Physical Performance and Magnesium

A further point to be made is to highlight the effect of Mg supplementation (in those with Mg deficit) on age-related physical performance decline. It has been shown that a 12 week course of 300mg per day of Mg oxide was sufficient to improve the muscular and physical performance of the hands and legs of a group of ladies of approximately 70 years of age(50).

The importance of this can not be understated, as it indicates that even if age or disease related health has been prolonged over a large number of years, Mg supplementation can be of benefit to help assist people to be more active and healthy.

 #5 Diabetes and Magnesium

Another important function of magnesium is its role in glucose metabolism(34-35). Simply put, reductions in Mg concentration can lead to increased insulin resistance, a common precursor to the development of diabetes(36).

Conversely, insulin resistance can cause Mg deficiency(36). One of the underlying factors which lead to these changes is the increased loss of Mg through urination in those suffering with diabetes(17).

The relationship between Mg intake and diabetes has been observed through pooled data from a number of studies. For example, a meta-analysis of 7studies (286,668 participants) found that over 6-17 years, an increase in 100mg per day of magnesium intake led to a 15% reduced risk of diabetes(34).

What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage

These results were further supported by two other prospective longitudinal studies(37-38). In the first(37) a 23% relative risk reduction between those with the highest Mg intake compared to the lowest intake. In the second study(38) an dose-response inverse association was found between Mg intake and diabetes risk; but statistical significance was only observed in those with body mass index of >25. Perhaps indicating a greater risk in those individuals who are both Mg deficient and overweight.

When compared for effectiveness against placebo the results are not as clear(35, 39). For example, in a group of 128 poorly controlled diabetics, glycaemic control only was improved with dosages of 1000mg/ day of Mg oxide(40).

However, in a similar patient group given just 300mg of magnesium chloride per day, fasting glucose was significantly reduced over 16 weeks(41). Sadly these results were not replicated in patients provided 369mg of Mg aspartate per day(42). These mixed results explain why institutions such as The American Diabetes Association do not recommend officially that the benefit of magnesium supplementation is sufficient to improve glyaemic control in diabetes(39); and why they also state that the evidence is not clear for supplementation outside of those with a Mg deficit.

Effectiveness may be relative to the form of magnesium provided and the dosage. Therefore, with Mg deficiency being possible in such a varied spectrum of the population and the “invisible” nature of the deficit, Mg supplementation may remain something for those with insulin resistance or DM to consider.


Magnesium | Dosage

The recommended daily allowance for magnesium ranges from 400-420mg per day in males, and 310-320mg per day in females(46).

The tolerable intake levels for supplementary magnesium are different and in children this would reduce to 65mg between ages 1-3, 110mg for ages 4-8, 350mg for ages 9-18, and 350mg for 19 years +(46).

Further supplementary dosages for specific risk factors are as follows:

Age related physical performance

300mg per day (magnesium oxide)- 12 weeks(49)

Blood Pressure

>370mg better reduction in BP(28)

Heart disease

Up to 250mg per day associated with a significantly lower risk of ischaemic heart disease(30-32)


100mg of dietary Mg associated with an 8% reduction in risk of stroke(33)


100mg reduces risk of DM by 15% (statistically significant)(34); however greater benefits are seen on glycaemic control at higher rates (between 300-1000mg) when compared to placebo(40-41). Between 4-16 weeks duration of intake is appropriate.

Bone Mineral Density

290mg/ day magnesium citrate for 30 days suppressed bone turnover(47)

Dosages of >5000mg/ day are associated with toxicity(55).


Magnesium | Side Effects


Toxicity of magnesium is generally prevented in healthy individuals as the kidneys eliminate excess Mg in urine (50); however dosages beyond 5000mg per day have been associated with mortality in both children (51) and older adults (52).

Normal side effects from high dose consumption

Diarrhea, nausea and abdominal cramping.

This is particularly evident with high doses of magnesium carbonate, chloride, oxide and gluconate (18). The laxative effect of excessive consumption is due to magnesium salts being unabsorbed in the intestine and colon, which modifies movement of fluids and stimulates gastric motility.

Symptoms of potential toxicity

These include hypotension, nausea, vomiting, facial flushing, urinary retention (not being able to fully empty your bladder), lethargy and muscle weakness, breathing difficulties and cardiac arrest(50).

Caution should be taken with supplementation in the presence of impaired renal function (kidney disease) due to the inability to remove excess magnesium (50).

Taking other medications?

Another consideration is the impact of magnesium supplementation when taking other medications. For example, magnesium supplementation should be separated from the use of oral biphosphonates (used to treat osteoporosis) by 2 hours to prevent dampening the effect of the medication (53).

Additionally anti-biotic medications from the tetracycline family (e.g. doxycycline) should be taken either 2 hours prior to, or 6 hours following a magnesium supplement (54). Medications such as potassium-sparing diuretics (e.g. spironolactone) will reduce frequency of urination and reduce excretion of magnesium- therefore caution should be taken to avoid toxicity.


Take Home Message


And so concludes the first part of our magnesium saga… So far we have learnt that deficiency in magnesium concentration is common, and that having a deficiency can lead to a number of age related disease states characterised by increased oxidative free radical activity, glucose metabolism changes and bone formation imbalance.

Alternatively, we have also seen the apparent benefits of supplementation to counteract the risk of disease and prevent deficiency.

In part 2 of this piece we will explore the ergogenic benefit of magnesium supplementation, and whether it can not only sustain health as we age- but also whether it can improve athletic performance!

Many thanks,


What Is Magnesium? | Health Benefits, Side Effects & Supplement Dosage


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