By Brian Lau, M.D., for ABC News:

Doctors have long known that the sooner a stroke is treated, the better the outcome. But now a new study finds just how much each minute counts.

For each 15-minute head start doctors get on treating stroke, they cut the risk of stroke symptoms and death by 4 percent, according to the study of more than 58,300 ischemic stroke patients published Tuesday in the Journal of the American Medical Association. What's more, every 15 minutes also improves how you leave the hospital, with a 4 percent increased likelihood of walking out and a 3 percent increased chance of heading home instead of going to a rehab center or nursing home.

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A stroke is a major reduction in the normal flow of blood to the brain. A person dies from stroke every four minutes in the U.S., according to the U.S. Centers for Disease Control and Prevention - that's almost 130,000 Americans each year, making strokes one of the leading causes of death in the country. More than half of stroke survivors age 65 and older lose the ability to walk.

This new study is 30 times larger than the latest trials that evaluated stroke treatment, factoring in data from nearly 1,400 hospitals - and not only large academic hospitals but community medical centers as well. In other words, these findings are more likely to be what the average American experiences.

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Study author Dr. Jeffrey Saver, director of UCLA's Comprehensive Stroke Center, said it's important to know that strokes are a treatable disease.

"Every minute that goes by without treatment, 2 million additional neurons are lost," Saver said in an email. "The demonstration of a substantial impact of even 15 minutes delay in starting treatment emphasizes the importance of the fastest possible evaluation and treatment of acute stroke patients."

Stroke experts emphasize that it is important to act FAST to receive appropriate medical help.

"FAST, stands for the need to act quickly if there are problems with Face, Arm or Speech function and not to waste any Time doing so," said Dr. Lee Schwamm, co-author of the study and vice chairman of neurology at Harvard Medical School.

Doctors Take:

Every minute counts. Recognize the symptoms of a stroke and get help as soon as possible. Every 15 minutes saved improves the chances you'll have a better outcome.

Tips

• Maintaining a healthy lifestyle with diet and exercise, and cutting smoking can prevent a stroke. If you have diabetes, be sure to take your medications and control your blood sugars;
• Think FAST - the American Heart Association's acronym for the warning signs of stroke: F - Face Drooping - Does one side of the face droop or is it numb? Ask the person to smile. Is the person's smile uneven? A - Arm Weakness - Is one arm weak or numb? Ask the person to raise both arms. Does one arm drift downward? S - Speech Difficulty - Is speech slurred? Is the person unable to speak or hard to understand? Ask the person to repeat a simple sentence, like "The sky is blue." Is the sentence repeated correctly? T - Time to call 911 - If someone shows any of these symptoms, even if the symptoms go away, call 911 and get the person to the hospital immediately. Check the time so you'll know when the first symptoms appeared.