Magnesium – is it more important for athletes than we thought?

 The mineral magnesium is something of a ‘Cinderella’ nutrient. Most sportsmen and women know that it’s required for health, but few really appreciate its importance for sport performance. And now, as Andrew Hamilton explains, new research suggests that an optimum magnesium intake could be even more vital than we previously believed.

Think of the ‘big hitters’ in minerals for sports nutrition and the chances are you’ll come up with iron, calcium and perhaps zinc. Yet despite magnesium’s pivotal role in energy production, many coaches and athletes remain unaware of its critical importance in maintaining health and performance. To make matters worse, magnesium is a mineral that is often poorly supplied in the diet; dietary intakes of magnesium in the West have declined to less than a half of those recorded at the end of the 19th century and are still falling(1). Moreover, many nutritionists believe that the amount of magnesium required for optimum health has been underestimated in the past, and research suggests that even small shortfalls in magnesium intake can seriously impair athletic performance. This evidence includes the following :

  • A study on women put on a magnesium restricted diet, which showed for a given cycling workload, peak oxygen uptake, total and cumulative net oxygen utilisation and heart rate all increased significantly during the period of magnesium restriction, with the amount of the increase directly correlated with the extent of magnesium depletion (ie the magnesium deficiency reduced metabolic efficiency, increasing the oxygen consumption and heart rate required to perform a given workload)(2);
  • A study of male athletes supplemented with 390mg of magnesium per day for 25 days, which resulted in an increased peak oxygen uptake and total work output during work capacity tests(3);
  • A sub-maximal work study, which showed that magnesium supplementation reduced heart rate, ventilation rate, oxygen uptake and carbon dioxide production for a given workload(4);
  • A study on physically active students, which showed that supplementing with 8mg of magnesium per kilo of body weight per day produced significant increases in endurance performance and decreased oxygen consumption during sub-maximal exercise(5).

The likely explanation for these findings lies in the fact that that magnesium is required for the activation of crucial enzymes known as ATPases, which are required for the generation of ATP, the body’s ‘energy currency’ used for all muscular contraction (see box below). A magnesium shortfall also appears to reduce the efficiency of muscle relaxation, which accounts for an important fraction of total energy needs during exercise.

What is magnesium and why does it matter?

Pure magnesium is the second most abundant mineral in cells after potassium, but the 2oz or so found in the typical human body is present not as metal but as magnesium ions (positively charged magnesium atoms found either in solution or complexed with other tissues such as bone). Roughly one-quarter of this magnesium is found in muscle tissue and three-fifths in bone; but less than 1% of it is found in blood serum, although blood magnesium is used as the commonest indicator of magnesium status. This blood serum magnesium can further be subdivided into free ionic, complex-bound and protein-bound portions, but it’s the ionic portion that’s considered most important in measuring magnesium status, because it is physiologically active.

Magnesium is required for more than 300 biological reactions in the body, including those involved in the synthesis of fat, protein, and nucleic acids, neurological activity, muscular contraction and relaxation, cardiac activity and bone metabolism. Even more important for athletes is magnesium’s pivotal role in both anaerobic and aerobic energy production, particularly in the metabolism of adenosine triphosphate (ATP), the ‘energy currency’ of the body. The synthesis of ATP requires magnesium-dependent enzymes called ‘ATPases’. These enzymes have to work extremely hard; the average human can store no more than about 3oz of ATP, yet during strenuous exercise the rate of turnover of ATP is phenomenal, with as much as 15kgs of ATP per hour being continually broken down and reformed.

A study carried out using rats earlier this year provides further evidence of the magnesium/ lactate connection(7). Taiwanese researchers investigated the effects of administering pre-exercise magnesium (17mg per kg of body weight) on rats forced to swim for 15 minutes. In particular, they wanted to observe the effect of the supplemented magnesium on blood lactate, glucose and pyruvate (an important intermediate compound at the ‘crossroads’ of aerobic metabolism).

Prior to exercise, the blood levels of lactate, glucose and pyruvate were no different in magnesium-supplemented rats when compared with rats given no magnesium (control group). However, following the forced swimming, the lactate levels in the magnesium-supplemented rats rose to only 130% above pre-exercise levels compared with a 160% rise in the control group. Moreover, swimming caused brain glucose and pyruvate levels in the control group to decrease to 50-60% of the pre-exercise level; in the magnesium-supplemented rats, brain glucose levels increased to 140% of the pre-exercise level, and increased pyruvate levels to 150% of the basal level during forced swimming!

The researchers concluded that not only did supplemental magnesium help suppress lactate production, but that it also somehow increased glucose availability and metabolism in the brain during exercise. This is important because scientists now believe that the brain and central nervous system play a large role in determining the degree of muscular fatigue we feel(8); higher brain glucose availability could in theory translate into lower levels of perceived fatigue.

An antioxidant role for magnesium?

Until recently, magnesium has had something of a Cinderella status among sports nutritionists, many of whom have not appreciated just how important optimum magnesium status is for athletic performance. However, it now seems that magnesium has another surprise to reveal, as new research indicates it may play a vital role as an antioxidant, helping to protect the body from the potential ravages caused by oxidative stress (cellular damage occurring as a result of oxygen generated free radicals within the body.

Free radical damage describes the damage that occurs within cells (for example cell membranes and DNA) at a molecular level as a result of ‘free radicals’. These free radicals are transient but extremely reactive chemical species that are an unavoidable by-product of oxygen metabolism when fats, proteins and carbohydrates are combined with oxygen in the body to produce energy (aerobic metabolism). For this reason they are sometimes called ‘reactive oxygen species’ (ROS) or ‘oxygen radicals’.

Although our cells have very efficient antioxidant defence systems to quench and neutralise harmful free radicals, these systems are not 100% efficient, and over time biochemical damage gradually accumulates, leading to a reduction in cellular function. Most scientists now believe that accumulated cellular free radical damage lies at the heart of the ageing process and many degenerative diseases such as cancer, autoimmune diseases and Alzheimer’s disease. Athletes process and use larger volumes of oxygen and at higher rates than the majority of the population; this explains why many scientists believe that they may benefit from higher intakes of antioxidant nutrients to bolster defences.

Although other minerals such as copper, zinc and selenium are known to be involved in activating enzymes that deactivate free radicals and thus protect the body, the possible role of magnesium as an antioxidant nutrient is extremely surprising to say the least. That’s because unlike other antioxidants, magnesium is not ‘chemically speaking’ considered adept at accepting and passing on electrons (something that characterises all other antioxidant molecules). However, despite this fact, a growing body of recent evidence suggests that adequate dietary magnesium is essential for the control of oxidative stress.

One of the earliest studies to indicate a possible connection between magnesium and oxidative stress was conducted at the Military Medical Academy in Belgrade involving young military recruits exposed to chronic stress(9). The researchers monitored markers of oxidative stress such as increased superoxide anion (free radical) concentration and malondialdehyde (a marker of cell lipid damage) in each subject as well as magnesium status. They discovered that a low magnesium status was correlated with increased levels of oxidative stress and that the poorer the magnesium status, the higher the recorded oxidative stress.

“A growing body of recent evidence suggests that adequate dietary magnesium is essential for the control of oxidative stress”

Correlation of course isn’t the same as cause, but further evidence of a link between magnesium and oxidative stress surfaced three years later in an Indian study carried out on rats that were given an injection to make them diabetic(10). Compared to non-treated rats (controls), the diabetic rats showed a significant decrease in blood magnesium levels and an increased urinary excretion of magnesium. In addition, there was a marked increase in markers of cell damage and a corresponding decrease in the antioxidant vitamins C and E, and other protective compounds called thiols.

Interestingly however, giving the diabetic rats magnesium supplementation for four weeks restored blood magnesium levels to near normal levels and reduced markers of cell damage. Moreover, supplementing magnesium also boosted vitamin C and thiols, and increased antioxidant enzyme activity generally, suggesting a strong causal link.

Another very recent animal study examined the effect of a magnesium deficiency on free radical damage in cultured cells from chick embryos(11). In particular the researchers wanted to investigate whether magnesium deficiency enhanced the oxidative damage caused by a naturally produced pro-oxidant (a substance that enhances oxidative stress) in animal cells called hydrogen peroxide. They found that incubating the cells in a magnesium deficient environment doubled the amount of hydrogen peroxide produced and significantly enhanced cell damage caused by this compound. This effect was probably because the magnesium deficiency reduced the activity of an enzyme called catalase, which helps to break down and render harmless any hydrogen peroxide produced in the body. Other recent animal studies have also confirmed that low magnesium intake is strongly correlated with increased oxidative stress(12-15).

Antioxidant and anti-inflammatory activity of magnesium in humans

Animal studies are all very well, but can optimising magnesium status help protect the human body? Very few studies have been conducted in this area so far, but the evidence so far suggests this is quite likely. There’s certainly a growing body of evidence that low magnesium intakes are correlated with increased inflammation, which is itself strongly associated with oxidative stress.

For example, an Italian study carried out last year of over 1,600 adults showed that low intakes of dietary magnesium were correlated to increased levels of an inflammatory marker known as C-reactive protein(16); although this study looked at middle-aged sedentary adults, an increased tendency towards inflammation is undesirable in all populations, especially athletes, where it is generally associated with increased post-exercise muscle soreness and joint stiffness.

Another study looked at lung function and in particular whether dietary antioxidants might protect lung tissue against reactive oxygen species-induced injury, adverse respiratory effects and reduced pulmonary function(17). Healthy, non-smoking freshmen students who were lifetime residents in the Los Angeles or the San Francisco Bay areas of California completed comprehensive residential history, health history and food frequency questionnaires. Blood samples were also collected and forced expiratory volume (lung power) measurements were obtained. Using a statistical technique called multivariable regression, the researchers showed that the higher the intake of dietary magnesium, the more positive the lung function (indicating healthier more elastic lung tissue).

A third study published just a few months ago examined the effect of magnesium supplementation on inflammatory markers in patients with chronic heart disease(18). The study, conducted by Israeli researchers, compared the levels of the inflammatory marker C-reactive protein in patients given 300mg a day of magnesium citrate with a control group given no magnesium.

The result showed unequivocally that the extra magnesium produced a significant drop in C-reactive protein levels, indicating reduced inflammation, so much so that the researchers commented that ‘targeting the inflammatory cascade by magnesium administration might prove a useful tool for improving the prognosis in heart failure.’

Optimising dietary magnesium intake

Magnesium is well supplied in unrefined whole grains, such as wholemeal bread and whole grain cereals, and also in green leafy vegetables, nuts and seeds, peas, beans and lentils (see table below). Fruit, meat and fish supply poor levels, as do refined/sugary foods. Contrary to popular belief, milk and dairy products are not particularly rich sources of magnesium. Magnesium is a fairly soluble mineral, which is why boiling vegetables can result in significant losses; in cereals and grains, it tends to be concentrated in the germ and bran, which explains why white refined grains contain relatively little magnesium by comparison with their unrefined counterparts.

The UK recommended intake for magnesium is set at 300mg for men and 270mg for women(19). The US has recently revised its figures upwards and now recommends an intake of 400mg per day for men aged 19-30 and 420 for those over 30; the figures for women under and over 30 are 300 and 310mg per day respectively(20). However, some investigators believe that even these levels are too conservative and that they should be set even higher at 450-500mg/day for all adults(21).

Table 1: The magnesium content of some common foods

Food Magnesium content (milligrams per 100g)

Pumpkin seeds (roasted) 532
Almonds 300
Brazil nuts 225
Sesame seeds 200
Peanuts (roasted, salted) 183
Walnuts 158
Rice (whole grain brown) 110
Wholemeal bread 85
Spinach 80
Cooked beans 40
Broccoli 30
Banana 29
Potato (baked) 25
White bread 20
Yoghurt (plain, low fat) 17
Milk 10
Rice (white) 6
Cornflakes (‘Frosties’ or ‘Honeynut’) 6
Apple 4
Honey 0.6
 (source USDA Nutrient Database)

Implications for athletes

What does this all mean for athletes? The simple message is that a growing body of evidence suggests that maintaining an optimum magnesium status is probably even more important than we’ve previously realised (see box, right). The latest research on magnesium and lactate adds further weight to the evidence indicating that a healthy magnesium intake is vital for both endurance and anaerobic performance. In the longer term (and perhaps more surprisingly), it appears that an optimal magnesium intake may also be essential for antioxidant protection and for the correct regulation of inflammation, both of which are desirable for athletes, young and old. Although more research is needed to discover the underlying mechanism behind these effects, the take home message is that you should ignore the importance of magnesium at your peril!

Andrew Hamilton BSc Hons, MRSC, ACSM is a member of the Royal Society of Chemistry, the American College of Sports Medicine and a consultant to the fitness industry, specialising in sport and performance nutrition


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