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The 21-minute cure

Twenty-one minutes: That's about how long it takes for exercise to reliably reduce anxiety, studies show, give or take a minute. "If you're really anxious and you hop on a treadmill, you will feel more calm after the workout," Dr. Ramsey says.

"I generally ask my patients to spend 20 to 30 minutes in an activity that gets their heart rate up, whether it's a treadmill or elliptical or stair stepping—anything you like. If you rowed in college, get back to rowing. If you don't exercise, start taking brisk walks."

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