The dog days of summer heat are upon us. Most of us won't let that keep us indoors, but battling the heat while we have fun can be dangerous. What fluid is the right drink for preventing dehydration and problems from the heat?
Working muscles produce heat as a byproduct of metabolism. Evaporation of sweat at the skin is the body's cooling process. The blood vessels just below the skin are cooled by the evaporation process and as the blood flows back through the deeper organs to the heart, the rest of the body is cooled. Sweat does not evaporate as well in hot, humid conditions. This causes body heat to build up and increases sweating. But without evaporation, there is little cooling. Even just one percent of body fluid loss can cause symptoms of lightheadedness and dehydration. Even mild dehydration can cause fatigue, decreased coordination and cramping.
Conditioned athletes can lose 1.5 liters or more of fluid each hour of activity. To prepare for the loss associated with activity, a person must pre-hydrate before activity. Especially in hot weather, the gastrointestinal tract may not be able to keep up with sweat losses, and a degree of dehydration may be inevitable. The body does not store the fluid taken in preparation of activity, but pre-hydration ensures maximal hydration at the start.
Some coaches used to advocate going without water during practice because of their belief that the body would adapt and use less water. This is false and dangerous. Full hydration is extremely important for the safe and best performance. Drinking extra water does no harm and may be protective.
What fluid is best to prevent dehydration while exercising? For everyday active people, plain cool water is best. Water rapidly leaves the digestive tract to enter the body's muscles and tissues. The best temperature for the water is 59 to 72 degrees. This helps to cool the body from the inside. Replacing electrolytes and using carbohydrate drinks can cause blood flow change from muscles to the GI tract. This can change endurance and lead to stomach cramping. For athletes exercising for more than 90 minutes continuously, carbohydrates in the form of glucose, sucrose or maltodextrin should be ingested at a rate of 30 to 60 grams per hour. This helps maintain optimal muscle contraction and prevents fatigue. Higher concentrations of carbohydrate can lead to stomach cramps.
What about sports drinks?
Sports drinks have advantages over water for the athlete or person exercising at high intensity for more than 90 minutes. Replacing plain water over longer periods of exercise without replacing the electrolytes can lead to hyponatremia (low blood sodium concentration). For athletes exercising less than one hour continuously, a nutritionally balanced diet is usually all that is needed to replace electrolyte losses. For most athletes, water is more beneficial and causes less stomach upset.
What about caffeine?
Caffeine can boost performance for a short time; however, caffeine acts as a diuretic and can increase your risks of becoming dehydrated. Caffeine also can increase heart rate and change the heart's performance properties. It is better to use plain cool water.
Optimum performance is gained by pre-hydrating beginning 2 hours before exercise or performance. Cool water is the fluid of choice, unless extreme endurance is needed for greater than 90 minutes, then a sports drink with electrolytes and carbohydrates may be better.
DR. DRU HAUTER is board certified in internal medicine and specializes in occupational medicine and urgent care at HealthPoint in Normal, part of the BroMenn Medical Group.