When an older friend or relative slows down people take notice—and often start to worry. Although walking pace is a seemingly basic measure to make, it has been gaining traction in the gerontology world as a reliable marker for overall health and longevity for those 65 and older.

A new analysis of walking speed studies shows that—down to the tenth of a meter per second—an older person's pace, along with their age and gender, can predict their life expectancy just as well as the complex battery of other health indicators.

So instead of a doctor assessing a patient's blood pressure, body mass index, chronic conditions, hospitalization and smoking history and use of mobility aids to estimate survival, a lab assistant could simply time the patient walking a few meters and predict just as accurately the person's likelihood of living five or 10 more years—as well as a median life expectancy.

And with the first wave of baby boomers hitting 65 this year, this easy measurement could become a powerful clinical tool that might help doctors decide on cancer screening, cardiac surgeries and other invasive treatments.

Walking—or gait—speed is "a powerful indicator of vitality," says Stephanie Studenski, a professor at the University of Pittsburgh's Division of Geriatric Medicine and co-author of the new analysis. "We just didn't use it in health care or public health."

With more people living longer, there is a growing disparity in older adults' health, "making it increasingly difficult to distinguish merely old (chronologically aged) from geriatric (biologically aged) patients," Matteo Cesari, of the Campus Bio-Medico University of Rome's Department of Geriatrics, wrote in an editorial accompanying the new study. For example, he noted, cancer patients who are "old" but not "geriatric" might be better candidates for more aggressive treatments, and similar distinctions could be helpful for cardiologists trying to make decisions about major surgeries for older patients.

The trick has been "being able to turn that gestalt into something that's measurable," Studenski says. "I think doctors even have this [viewpoint], but it's invisible in health care," she says, noting that walking speed is not usually described in medical records or other clinical notes. She hopes that her work will give walking speed "a more overt reality by measuring it."

The new analysis, published online January 4 in JAMA The Journal of the American Medical Association, found that walking speed turned out to be a consistent predictor of survival length across age, race and height categories, but it was especially useful in zeroing in on life expectancy for those who still live and get around independently and for those older than 75.

Despite its apparent variability in clogged grocery store aisles and busy sidewalks, individual "people have a remarkably stable preferred walking speed," Studenski notes. "Your body sort of self-selects your walking speed that best accommodates all of the systems that are needed to walk," she explains. And although walking might seem like a simple mode of locomotion, it is a biologically complex endeavor, she notes, which integrates the circulatory, respiratory, skeletal, muscular and nervous systems.

For the new paper Studenski and her colleagues analyzed nine cohort studies of community-dwelling adults 65 and older. Of the 34,485 adults in the studies, people with average life expectancy walked at about 0.8 meter per second. For those with a gait speed of one meter per second or faster "survival was longer than expected by age and sex alone," the researchers noted in their article.

But before people race out to time their paces, Studenski cautions, the test, although it is simple and requires no formal medical background, needs to be done in a controlled environment and executed by someone who has been trained to do it properly.

Even when done correctly, it is not a perfect measure. "Just like your blood pressure is one indicator of your health, it doesn't tell you everything—your walking speed doesn't either," Studenski says. If the correlation of walking speed with life expectancy—and possibly treatment decisions—gains prevalence in popular practice however, would people undergoing a walking test not be tempted to hedge their bets and pick up the pace? Studenski notes that those in the studies analyzed were not told the reason their pace was being measured. And like other health tests, "there's always a human element" that introduces some variability, she says, noting the example of "white coat hypertension" in which a person's blood pressure rises "because they're nervous that their doctor is measuring their blood pressure."

What might be more meaningful, she notes, is tracking a person's walking speed over time, which might alert a physician to new underlying problems if the pace drops off. From there, she adds, doctors could start to investigate what body system might be slowing them down. With further investigation, walking speed might also help sort out not just how long a person is going to live but also how long they are likely to maintain independence and a high level of function.

The research on walking speeds and longevity has yet to determine if adopting a quicker pace can actually help someone live longer, or whether speed is simply an independent indicator. "Gait speed should not be considered as a primary target for interventions at this time," Cesari noted in his editorial.

Research by Studenski and her colleagues had found that people whose gait speed improved over the course of a year did have an increased rate of survival. But, she says, "we are not saying people should go out and walk faster." Because there have been no clinical trials offering fast walking as an intervention, a quick pace is not a proved panacea for living longer. Many other studies have, however, found that walking helps lower blood pressure, keep weight down and improve mood. Substantial amounts of strolling have also been linked to slower memory decline and reduced risk of some cancers.