In his classic book Optimum Sports Nutrition, Dr Michael Colgan called vitamins and minerals the nuts and bolts of a healthy athlete, and for good reason. Vitamins and minerals act as cofactors in enzyme driven reactions, and this therefore makes them essential at connecting the various metabolic pathways together. Without vitamins and minerals, deficiency diseases develop due to a breakdown in metabolic regulation. Vitamin and mineral deficiencies are rare in the Western nations due to the large amounts of food we have available. However, increasingly such populations are turning to Western style foods that are devoid of vitamins and minerals and as a result many individuals only have borderline intakes of their essential nutrients. These low intakes are not enough to cause outright deficiencies, but instead cause vitamin and mineral insufficiencies, a new classification that is characterised by subclinical symptoms that can lead to malaise, general poor health and symptoms that appear to have no particular cause.
Athletes are at particular risk of developing insufficiencies of essential nutrients because they have an increased requirement for these nutrients due to their physical activity. In particular mineral requirements increase because sweat contains high concentrations of minerals and these minerals must be replaced through the diet. Studies designed to test the effects of mineral supplements in human athletes have generally been poorly designed because researchers seem to have an inability to fully comprehend human nutrition. To these ends many studies have tested mineral supplements in the short term like drugs, rather than over extended periods for a number of years, which is how long it often takes to reverse some mineral insufficiencies. That being said, a role for an increased requirement of minerals in athletes diet has been shown in some studies, although finding useful data is laborious and time consuming. The case for iron supplements in female athletes is fairly well established, but other minerals have not have the same levels of funding and interest.
Magnesium is one mineral that has been researched in the nutritional literature in regard to its requirements in athletes. Sweat contains high concentrations of magnesium, and so the increased perspiration rates of athletes suggest that increase dietary intakes may be a requirement. This requirement will be supplied by the diet if nutrition is of a high quality because along with an increased requirement for essential nutrients will come an increased calorie intake. In addition, evidence in the nutritional literature looking at the diets of athletes shows that many choose to consume a multivitamin and mineral supplement which can ensure an adequate intake of most of the essential nutrients. Magnesium is available in foods including grains and green leafy vegetables and consuming these foods should provide adequate dietary magnesium. Those athletes not consuming adequate magnesium may experience a deterioration in muscle function as well as changes to the maximum oxygen carrying capacity of blood.
In one study researchers investigated the relationship between oxygen consumption and the magnesium status of trained and untrained university students1. As expected the maximum oxygen consumption was higher in the trained students due to their increases muscle mass and increased efficiency in their cardiovascular systems. The plasma magnesium levels of the trained students was strongly correlated to their oxygen consumption and this association remained even after the researchers controlled for the amount of haemoglobin in the blood. However, in the untrained students, the association between plasma magnesium and oxygen consumption was much weaker. The authors concluded from this that ionic magnesium may play a role in facilitating the delivery of oxygen consumption to working muscles and that higher plasma magnesium concentrations may therefore increase the efficiency of the cardiovascular system. In particular magnesium may facilitate the production of 2,3-diphosphoglycerate (2,3-DPG) in the erythrocyte, a compound that has the ability to allow oxygen release from haemoglobin when close to respiring tissue.
Dr Robert Barrington’s Nutritional Recommendation: Magnesium and other macrominerals are often required in higher amounts in the diets of athletes compared to sedentary individuals. The ability of magnesium to improve the efficiency of the cardiovascular system in athletes through increased 2,3-BPG production is interesting because magnesium is also known to decrease the risk of cardiovascular disease. By increasing 2,3-BPG concentrations in red blood cells, magnesium allows improvements in efficiency and this may explain its cardioprotective role. Deoxygenated haemoglobin causes a net release of magnesium ions in red blood cells, and this inhibits the enzyme hexokinase, which stimulates glycolysis and the production of 2,3-BPG. Low intakes of magnesium may decrease plasma magnesium concentrations and reduce the availability of magnesium to inhibit the hexokinase enzyme.
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