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In 1965, the Yamasa Clock and Instrument Company launched a device they called “Manpo-kei,” a Japanese phrase that loosely translates as “10,000 steps meter.” This pioneering pedometer was a big hit – as was the notional goal its name suggested.

These days, thanks to the proliferation of wearable technology, step counting is ubiquitous and 10,000 steps is widely accepted as a default daily goal. But research presented at the American College of Sports Medicine conference in Orlando earlier this month offers a reminder that a catchy gadget name and a conveniently round number don’t necessarily make for good science. The right step goal to optimize your health depends on who you are – and, it turns out, what type of step counter you’re wearing.

The first study, from a research team led by epidemiologist I-Min Lee of Harvard University’s T.H. Chan School of Public Health, analyzed a week’s worth of step data from nearly 17,000 people in the Women’s Health Study, then tracked their health for up to eight years after the measurement. The women in the study had an average age of 72 and took an average of 5,499 steps a day.

While previous studies have linked step counts to changes in proxy health risk factors such as blood pressure and body weight, there’s very little data on actual lifespan. In the new study, whose results appear in JAMA Internal Medicine, more than 500 subjects died during the follow-up period – and their step counts had striking predictive powers.

When divided into four equal groups, those in the second-lowest group, who averaged 4,363 steps a day, were 41 per cent less likely to die than those in the lowest group, who averaged 2,718 steps a day.

Those in the highest quartile, at 8,442 steps a day, were somewhat better off, at 58 per cent less likely to die during the study. But the biggest gains came from simply getting out of the lowest group, not from racking up huge numbers: Beyond about 7,500 steps a day, the researchers concluded, the mortality benefits levelled off.

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That doesn’t mean we should toss out 10,000 steps quite yet, though. Another study presented at the ACSM conference, this one from a research group at the U.S. National Cancer Institute, assessed step counts in nearly 5,000 adults older than 40 between 2003 and 2006, then followed up a decade later, by which time more than 1,000 of the subjects had died.

Once again, the results showed that more steps were better. For every increase of 2,000 steps, the subjects were 46 per cent less likely to die of cardiovascular disease during the study, 21 per cent less likely to die of cancer and 36 per cent less likely to die of any cause. In this case, the benefits persisted up to – wait for it – 10,000 to 12,000 steps before plateauing.

The obvious reason for the contrasting results is that the studies had different populations: The Harvard study focused on older women, while the National Cancer Institute study looked at men and women across the age spectrum (starting at 40) in proportions mirroring the U.S. population at large. Women in their 70s, the data suggests, probably need fewer steps than people in their 40s to optimize their health.

But the more interesting point, according to Lee, is where the two data sets agree. “What is common about both our studies,” she says, “is that a modest increase in step count of an additional 2,000 steps per day over what one is already doing, among those not doing much, is associated with significantly lower mortality rates.”

And there’s one final wrinkle: Step counts depend on how you measure them. At the ACSM conference, researchers from Central Michigan University presented data comparing the carefully validated hip-mounted pedometers used in research with the simpler wrist-mounted activity monitors that are popular. Due to misclassified movements, they found that you’d need to take about 11,500 “steps,” as counted by the wrist-mounted device, to hit 10,000 on the research pedometer.

The best number to focus on, then, isn’t a universal goal; it’s your personal baseline. Sure, there’s a point of diminishing returns somewhere (“It makes sense,” Lee admits, “we can’t live forever”). But for most of us, the equation is simple: figure out how many steps you’re currently taking, then find a way of doing more, and odds are you’ll live longer.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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