What’s in your sweat?

Let’s face it; exercise can be a very sweaty undertaking. And while we may accept perspiration as a natural and healthy consequence of physical exertion, how much thought do we ever give to the effect that sweating has on the body?

For years, emphasis has been placed on the importance of staying properly hydrated during exercise, and maintaining the body’s sodium levels has become a key priority, particularly in elite athletes.

New research has assessed how the sodium lost through sweat influences the maintenance of stable and physiologically sound conditions that allow the body to carry out its functions.

Researchers from the Exercise Physiology Laboratory at Camilo Jose Cela University focused their analysis on the effect of perspiration in endurance events, such as marathon running, where several litres of sweat can be lost.

During the study, the electrolytes present in the sweat of a group of 51 marathon runners were analysed using patches on the skin specifically designed to collect sweat samples. In addition, a blood sample was also taken from each runner immediately after completing the race to determine the concentration of electrolytes in their blood.

This allowed the runners to be classified into three groups depending on their sodium concentrations; runners with low-salt sweat, runners with typical/normal amounts of sodium in their sweat, and salty sweaters, who had an excessive amount of salt in their sweat.

According to the results, the marathon runners who had high concentrations of electrolytes in their sweat had lower electrolyte levels in their blood, despite having properly rehydrated. This indicates that electrolyte levels in sweat can affect water and electrolyte stability in the body during the course of the marathon, hence sweat electrolyte levels impact on the conditions that allow the body to carry out its functions.

Beatriz Lara, head author of the study, explained, ‘We do not only lose fluids when we sweat, but the levels of several electrolytes that are essential to fluid balance and neuromuscular functioning also decrease, especially sodium.’

This can become a serious problem when the excessive loss of electrolytes through sweat is not properly replaced with food or beverages. In severe cases this can lead to hyponatraemia, a low sodium concentration in the blood that can cause decreased consciousness, hallucinations, brain herniation, and even death.

Lara adds, ‘Electrolyte concentration in sweat is an essential factor for predicting sodium requirements during sports activities, especially endurance activities such as marathons.’ In some cases, individuals with very salty sweat may benefit from supplements such as salt tablets.

Source: Scandinavian Journal of Medicine and Science in Sports