Read: The ennui of the Fitbit

I-Min Lee, a professor of epidemiology at the Harvard University T. H. Chan School of Public Health and the lead author of a new study published this week in the Journal of the American Medical Association, began looking into the step rule because she was curious about where it came from. “It turns out the original basis for this 10,000-step guideline was really a marketing strategy,” she explains. “In 1965, a Japanese company was selling pedometers, and they gave it a name that, in Japanese, means ‘the 10,000-step meter.’”

Based on conversations she’s had with Japanese researchers, Lee believes that name was chosen for the product because the character for “10,000” looks sort of like a man walking. As far as she knows, the actual health merits of that number have never been validated by research.

Scientific or not, this bit of branding ingenuity transmogrified into a pearl of wisdom that traveled around the globe over the next half century, and eventually found its way onto the wrists and into the pockets of millions of Americans. In her research, Lee put it to the test by observing the step totals and mortality rates of more than 16,000 elderly American women. The study’s results paint a more nuanced picture of the value of physical activity.

“The basic finding was that at 4,400 steps per day, these women had significantly lower mortality rates compared to the least active women,” Lee explains. If they did more, their mortality rates continued to drop, until they reached about 7,500 steps, at which point the rates leveled out. Ultimately, increasing daily physical activity by as little as 2,000 steps—less than a mile of walking—was associated with positive health outcomes for the elderly women.

Read: How self-tracking apps exclude women

That nuance can mean a lot to people who want to be less sedentary but aren’t sure how to start or whether they can do enough to make a difference, says Lindsay Wilson, a clinical professor of geriatric medicine at the University of North Carolina School of Medicine. “I don’t think setting the bar at 10,000 steps is a very successful way to approach exercise,” she says. “Some people are not walkers. They don’t have safe neighborhoods, or they feel unsteady on sidewalks. You need to be more creative. Is this a person who needs to go to a gym class or the pool, or sit on a stationary bike?”

Wilson says that’s especially true for the elderly patients she treats, but that the principle is safe to generalize. Adding in a little extra physical activity is good for most people both physiologically and psychologically, regardless of goals or benchmarks. At the same time, setting the same goal for everyone can be discouraging to the people who need activity the most.

If many of the persistent myths of American health, like eating breakfast and getting a certain number of steps, are based on marketing rather than science, why do they stick so well? “A big challenge is that the public and the media want cut-and-dried, black-and-white messages and findings, and science just doesn’t operate that way,” says Virginia Chang, a physician and sociologist at the NYU College of Global Public Health. “The uncertainty in the research doesn’t get translated well into the messaging. People just want to know what they should do.”