Top off your fluid level to beat the heat

Stay hydrated to beat the heat and humidity.

It’s summer in Chicago, and that means heat and humidity are high. The conditions can pose a challenge if you’re trying to work a jog or bike ride into your day. By keeping yourself well hydrated, you can keep up a healthy exercise regimen, even in the hot summer months.

The body typically cools itself by increasing surface blood flow or, on a windless day, by relying mainly on evaporation. Add humidity to the summer heat, and our body’s air conditioning system is severely taxed.

That’s where hydration can help.

First, if you are unaccustomed to exercising in summer conditions, give yourself a chance to acclimate by building up your workout routine. It generally takes about two weeks for the body to fully adapt to warm weather.

With heavy exertion, an individual may lose up to 3 pounds of fluid per hour. During exercise, 150 to 200 milliliters of fluid need to be replaced every 10 to 15 minutes. Water suffices for most activities. A typical diet helps the body maintain an acceptable electrolyte balance by replacing salt lost in perspiration.

For those whose exercise interrupts meals, sports drinks supplement calories while hydrating. Sports drinks containing 4 to 8 percent glucose sugar are readily absorbed. Higher glucose concentrations tend to reduce the time it takes to empty the stomach, leading to possible cramping, and excessive fructose sugar levels can produce diarrhea.

For those participating in high-endurance events, electrolyte replacement is critical. Drink fluids with electrolytes every 10 to 15 minutes during exercise.

What you do prior to exertion in the heat also has a big impact on your heat tolerance. Alcohol can increase urine output, dehydrating you. It also can influence blood flow to the skin’s surface, alter the body’s temperature set point, and potentially worsen heat stress by diminishing salt and water retention. Avoid alcohol 24 hours prior to competition or exercise. If you do decide to imbibe alcohol after exercise, rehydrate first and take the alcohol with a meal.

We’re stuck with what weather we’re dealt. How we weather the weather is largely up to us.

—Brian Svazas, M.D., M.P.H.