The findings do not mean that slow walkers are doomed to die early, the researchers warn. Nor will intentionally pushing yourself to hustle keep you young.
Instead, the study suggests that, like blood pressure and cholesterol levels, the pace that you feel comfortable walking at can be a simple sign of your overall health.
In turn, a simple walking test could help doctors and patients make decisions about when to perform certain screening tests -- and when not to.
"We are not saying that if you just go out and walk faster, you will live longer. Absolutely not," said Stephanie Studenski, a geriatrician at the University of Pittsburgh Medical Center and at the Veteran Affairs Pittsburgh Healthcare System. "We are saying your body selects a walking speed that is best for you based on the health of all your body systems."
"The best way to live as long and well as you can is to be in the best health you can be," she added. "Walking speed might help you reflect or monitor how healthy you are."
There has long been a sense that slowing down is an ominous sign of
aging, and not just in people. As pets get older, they may need more
rest stops during their morning walks. Even C. elegans worms that wiggle slowly die sooner than worms of the same age that wiggle more quickly.
"Whether you're conscious of it or not, you may feel like grandpa's doing pretty good because he's got a spring in his step, he's out moving around, and he looks lively. But I'm worried about Aunt Mary because she's slowing down a lot," Studenski said. "The observation that there's something about how well you move that reflects health is almost implicit in human experience."
To test that notion, Studenski and colleagues gathered data from nine large, long-term aging studies that included a total of nearly 35,000 people, ages 65 and up. Each study had collected walking speed measurements and survival rates dating back between six and 21 years.
Next to age and gender, the study found, the time it took a person to walk comfortably down a hall for a few yards was one of the best predictors of whether he or she would be alive five or 10 years later.
In fact, the researchers report today in the Journal of the American Medical Association that walking speed was as good at predicting lifespan -- if not better -- as were more complicated measurements, such as blood pressure, weight, smoking status and markers of heart disease and diabetes.
Based on the data, the researchers created a chart, much like a growth curve, which estimated life expectancy based on a person's age, gender and walking speed.
They found that people who normally ambled at about 2.2 miles per hour (extrapolated from a measured speed of 0.8 meters per second) tended to live the average amount of time expected for someone their age. For every 0.1 meters per second faster they chugged along, their chances of dying in the next decade dropped by 12 percent.
A 70-year-old man, for example, could expect to live anywhere from seven to 23 years. A 70-year-old woman would likely to live another 10 to 30 years. The faster they walked, the more likely they were to land on the longer-living end of the spectrum.
The reason walking speed is such a good predictor of mortality, Studenski suspects, is that so many organ systems are involved in how quickly we move, including the heart, lungs, blood, brain, nervous system, muscles, joints and bones. Still, she warned, the study is based on statistics and chances, and there are bound to be outliers: Slow-walkers who live a long time and fast-walkers who die early.
Given the strong relationship found between walking speed and mortality, the study offers a useful tool for doctors as they help older patients make health-care decisions, said Seth Landefeld, director of the University of California, San Francisco -- Mt. Zion Center on Aging.
Screening tests for cancers and heart disease, for example, are only helpful in people who are going to live for another five or 10 years, he said. A simple walking test could help determine whether it's worth doing those tests or taking other preventative measures. Walking speed can also be a good way to start conversations about expectations for the final years or decades of life.
Everyone slows down as they age, Landefeld added. But there are things people can do to slow down less.
"There is a lot of evidence that people who keep up physical activity as well as social activity do much better in all sorts of ways," he said. "They live longer. They have better health. Their mental health stays sharper. I would say this article reinforces the use-it-or-lose it message. If you keep walking and moving around, that will likely have benefits in terms of survival and overall health."