Thirst may not be the best indicator

The American College of Sports Medicine (ACSM) is pleased the recent Institute of Medicine (IOM) report, which set dietary intake levels for water, salt, and potassium for the maintenance of health and well-being, also indicates athletes and other active people have higher fluid replacement needs.

"This report is important because it debunks some common misconceptions about fluid and electrolyte intake. However, it is important to clarify the report's use of the phrase 'on a daily basis.' Daily fluid intake is governed mostly by behavioral factors, such as eating meals or even walking past a water fountain. Thirst is important during and after physical activity, especially in hot environmental conditions," said ACSM President W. Larry Kenney, Ph.D. "However, the clear and important health message should be that thirst alone is not the best indicator of dehydration or the body's fluid needs."

Dehydration resulting from the failure to adequately replace fluids during exercise can lead to impaired heat dissipation, which can elevate body core temperature and increase strain on the cardiovascular system. Dehydration is a potential threat to all athletes, especially those who are not acclimatized for strenuous activity in hot environments.

To minimize the potential for heat exhaustion and other forms of heat illness, Kenney and other ACSM experts recommend water losses due to sweating during exercise be replaced at a rate close to or equal to the sweating rate. This can be accomplished by athletes weighing themselves before and after the exercise bout. This recommendation is based on sound scientific data and clinical experience dealing with athletes suffering from heat-related illness.

"Relying on thirst to determine an active individual's fluid replacement needs is inadequate, especially so in older exercisers. As we age, thirst becomes an even poorer indicator of the body's fluid needs," said Kenney.

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