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It’s not the heat: How humidity affects your heart

Hot weather can lead to dehydration, heat exhaustion and heat stroke, but it doesn’t take soaring temperatures to pose a danger when you add humidity to the mix. The risk for these life-threatening conditions increases when the temperature rises above 70°F and the humidity registers more than 70 percent.

People with high blood pressure, heart disease, lung disease or kidney disease are most vulnerable to the effects of humid conditions, as are those over age 50 (our bodies’ ability to respond to summer heat decreases as we age). Other risk factors that can affect your body’s ability to cool itself include being obese; having poor circulation; following a salt-restricted diet; drinking alcohol; having inefficient sweat glands; and taking diuretics, sedatives, tranquilizers or heart or blood pressure medication.

Exercising in humid weather

Since you generate heat during exercise, humidity can affect your heart rate when you work out, even at cooler temperatures. Here’s how: Your body cools itself by sweating—but only if sweat can evaporate. In humid weather, sweat evaporates more slowly, so your body temperature continues to rise. What’s more, fluid loss from sweating decreases your blood volume. So while your heart is still working to cool you off, it must also work harder and faster to get that smaller amount of blood to your working muscles. That’s why it’s always important to replenish the fluids you lose by drinking plenty of water while you exercise.

Learn the warning signs

Recognize the warning signs of heat stress and take immediate action. Headache, fatigue, profuse sweating, muscle spasms or cramps, cold and clammy skin and swollen ankles and feet can mean you’re getting too hot. Move to a cool or air-conditioned area, drink fluids, shower in cool water and lie down. Seek emergency medical help if symptoms don’t improve quickly or if they progress to include nausea; dizziness; confusion; combativeness; warm, dry skin with no sweating; rapid pulse; high fever; or fainting.

Your best bet is to ward off heat illnesses before they occur. Pay attention to weather reports. Heat disorders can occur any time the temperature and humidity both rise above 70 or the heat index is greater than 80°F. Drink plenty of fluids, avoid caffeine and alcohol, limit activity to a cooler hour and wear light-colored clothing made of natural fabrics.