• Mayo Clinic Minute: Know the facts on stroke

Stroke is the fifth-leading cause of death in the U.S., according to the Centers for Disease Control and Prevention. It's also a leading cause of disability. But, when treated soon after symptoms start, the effects of stroke often can be lessened or reversed.

May is National Stroke Awareness Month, and the National Stroke Association wants everyone to know the signs and symptoms of the disease.

Watch: The Mayo Clinic Minute

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When someone's having a stroke, time is brain.

"Stroke is a term that we use for a sudden loss of neurologic function," says Dr. David A. Miller, a Mayo Clinic radiologist.

He says the faster you get treatment, the better the chances are of recovery. The most common type of stroke is called an ischemic stroke.

"[An ischemic stroke] is an interruption of blood flow, usually from a clot or other blockage of a vessel to the brain," says Dr. Miller.

Stroke can cause paralysis and make it impossible to communicate. If you're around someone who suddenly can't speak, has slurred speech, can't use an arm or leg, or suddenly loses vision, call 911.

"If stroke is recognized immediately and treated within a proper time frame, very often the signs and symptoms can be reversed," says Dr. Miller.

Clots can be dissolved with medication or sometimes removed. But treatment is most effective the sooner it's started. So don't wait. Call 911 because, when it comes to stroke, time is brain.