People who exercise at least 45 minutes four or more days each week take off 25 to 50 percent less sick time from work, according to a study by the American College of Sports Medicine, reported by HealthDay News.

“This reduction in illness far exceeds anything a drug or pill can offer,” said David Nieman, a representative for American College of Sports and Medicine.

But if you’re already sick, don’t risk worsening your condition by forcing yourself to hit the gym. Nieman recommended you follow these guidelines for a healthy workout when you’re under the weather:

• Exercise only if your head cold hasn’t reached your chest.

• Choose walking instead of running. Research shows that moderate exercise doesn’t worsen colds.

• Stay in bed if you experience anything beyond mild cold symptoms, such as severe aches and pains and fever.

• Rest is best when you are recovering from anything other than a mild illness. Opt for time off before you start workouts again.

According to the article, Nieman also recommended participating in moderate levels of physical activity before you get your flu shot. Studies show this improves your immunity in the future.

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