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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 13
  1. M F Bergeron1,
  2. D S Senchina2,
  3. L M Burke3,
  4. S J Stear4,
  5. L M Castell5
  1. 1National Institute for Athletic Health and Performance, Sanford USD Medical Center, Sioux Falls, South Dakota, USA
  2. 2Biology Department, Drake University, Des Moines, Iowa, USA
  3. 3Australian Institute of Sport, Canberra, Australia
  4. 4Performance Influencers Limited, London, UK
  5. 5University of Oxford, Oxford, UK
  1. Correspondence to L M Castell, University of Oxford, Green Templeton College, Oxford OX2 6HG, UK; lindy.castell{at}gtc.ox.ac.uk

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Introductory remarks

This issue begins with a brief article on electrolytes, now popularly offered to athletes in supplement form, as a discrete product or as an ingredient of sports drinks. Two herbs are also discussed: echinacea and ephedra. Both plants are popular supplements of athletes worldwide, but the similarities end there.

Electrolytes

M F Bergeron

Electrolytes are negatively (anions) or positively (cations) charged substances that, when in solution, conduct an electric current. Major physiological electrolytes include Na+, K+, Cl and HCO3, while other electrolytes such as Ca2+, Mg2+ and trace elements are also found in the body in significant amounts. Na+, K+, Cl and HCO3 are primarily responsible for normal water distribution and homeostasis throughout the body via their effect on osmotic pressure. These major electrolytes also play an essential role in regulating heart and muscle function, maintaining pH and a number of other important biochemical reactions.

An athlete's demand for electrolytes increases with exercise and heat stress, as extensive sweating can mean both large water and electrolyte losses in addition to related changes in extra- and intracellular water distribution. Dehydration and an increase in plasma osmolality, which is primarily driven by Na+, will also stimulate osmoreceptors prompting an athlete to drink to maintain further or defend plasma volume.1 The primary electrolytes in sweat are Na+ (20–70 mmol/l) and Cl, with comparatively much lower levels of K+ (∼5 mmol/l) and even less Ca2+ (∼1 mmol/l) and Mg2+ (∼0.8 mmol/l).2 As the sweating rate increases, the concentration of Na+ in sweat increases correspondingly, even with the lower sweat Na+ concentrations observed after heat acclimation.3 With Na+ being the major cation of …

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