In Current Anthropology, Dr Louis Liebenberg describes how Xi San hunters in the Kalahari chase antelope. They wait until the hottest part of the day with temperatures often exceeding 40 degrees. Then, well-watered, they set off for periods of up to six hours without further sustenance – running after and tracking down their prey.
“Endurance running and persistence hunting may . . . have been crucial factors in the evolution of humans,” Liebenberg concludes.
Nature has conferred on humans the abilities to perspire freely – no animal species sweats more than humans – and to tolerate temporary dehydration. The sports drinks industry, however, portrays sweating and dehydration during exercise as portents of impending physiological disaster.
Central to sweating are electrolytes: substances which, when dissolved, separate into atoms that carry either a positive or negative electrical charge. Electrolytes are crucial for cellular function, with positively charged sodium and potassium involved in controlling fluid volume.
The normal blood sodium concentration is 135-145 millimoles/litre. Those of us eating typical Western diets consume about 8.5g of salt (sodium chloride) a day.
However, the sports drink industry asserts that salt loss in sweat causes sodium deficiency, whereas excess salt in one’s sweat indicates the presence of too much salt in one’s diet. It does not indicate a need to replace it by drinking sodium-containing sports drinks.
As Prof Tim Noakes observes in Waterlogged, the Serious Problem of overhydration in endurance sports (2012): "When athletes drink less than they sweat during exercise, their blood sodium concentrations either stay the same or they rise . . . "
The sports drinks industry ascribes important roles for sodium in the resolution of two conditions: exercise-associated hyponatraemia (EAH) and exercise-associated muscle cramps (EAMC).
EAH
EAH is caused by voluntary overdrinking. It is defined by a blood sodium concentration of less than 135mm/litre. Symptoms include nausea and headache, caused by brain swelling. There have been at least 16 documented fatalities and more than 1,600 documented cases of non-fatal EAH.
By contrast, there has not been a single documented case of an athlete dying from dehydration. Numerous evidence-based studies show that those who win long-distance races are often the most dehydrated.
Last year, CrossFit sponsored the third International EAH Consensus Development Conference in Carlsbad, California.
Sixteen acknowledged experts on the topic agreed that the single most important risk factor for EAH “is sustained, excessive fluid [water, sports drinks or other hypotonic fluids] intake in volumes greater than loss through sweat, respiratory and renal water excretion, so that a positive fluid balance accrues over time”.
“It is critical to emphasise that sodium-containing sports drinks, which are hypotonic, will not prevent EAH in athletes who overdrink during exercise, as all sports drinks have a significantly lower sodium concentration . . . The dilutional effect of volume excess overwhelms any positive effect of sodium and electrolytes in sports drinks.”
However, the Gatorade Sports Science Institute (GSSI) states: "The risk of hyponatraemia can be reduced by making certain that fluid intake does not exceed sweat loss and by ingesting sodium-containing beverages or foods to help replace sodium lost in sweat."
Russell Berger of CrossFit is adamant on the issue. "The claim that sports drinks can help prevent EAH is a bold-faced lie," he tells Health+Family. "The sodium they contain is ingested with a magnitude of fluid that overwhelms any supposed benefit."
EAMC
Two possible causes of EAMC have been suggested. The so-called neuromuscular control theory states that EAMC is triggered following skeletal muscle overload, when factors such as fatigue and muscle damage combine to increase nerve excitability.
However, Prof E Randy Eichner – with well-documented connections to the GSSI – endorses the idea that EAMC is caused by extensive sweating and a consequent sodium deficit caused by insufficient sodium dietary intake, stating in Current Sports Medicine Reports that "[C]ontrarians favour fancy theories like 'altered neuromuscular control'".
However, the "fancy theory" received support from Dr Kevin C Miller in Current Sports Medicine Reports. He noted that in 2014, two healthy high school American football players died of EAH after drinking large volumes of fluid to prevent EAMC.
“Underlying these tragedies is the belief held by many medical professionals and the general public that EAMC is caused by dehydration and electrolyte (for example, sodium) losses. Yet, new experimental and observational data . . . suggest that cramping may be due to changes in the nervous system.”
Last year a study in Sports Medicine – Open (2015; 1: 8) investigated 280 competitors in a 161km ultramarathon, concluding: "Impaired fluid and sodium balance did not appear to be an etiology of muscle cramping during an ultramarathon."
Co-author Prof Martin D Hoffman told The Irish Times: "Basically, we've found that whether considering supplemental sodium intake or total sodium intake, there is no evidence that sodium protects against muscle cramping, nausea or vomiting, or hyponatraemia in this population of ultramarathon runners during continuous exercise up to 30 hours in hot environments.
“Hydration status can also be maintained without sodium supplements and by drinking to thirst. Obviously, there is a need for caloric intake during such long bouts of exercise.”
Hoffman’s last point is important. For those adapted to a high-carbohydrate diet, consuming carbohydrates during endurance exercise improves performance. It is generally accepted that taking about 60g of carbohydrate/hr is the best strategy in events lasting more than two hours and there is evidence that specific mixtures of glucose/maltodextrin and fructose can boost carbohydrate uptake.
However, the evidence is clear that there is no need to consume extra sodium during exercise.
One ingredient crucial to improved performance cannot be found in any sports drink: a willingness to train hard. And, as Liebenberg indicated, let us remember the physiological benefits conferred on us by evolution – not by the sports drinks industry.
