Total Daily Steps, Not Speed, Linked to Lower All-Cause Mortality

By Lisa Rapaport

March 25, 2020

(Reuters Health) - Higher daily step counts, but not speed, are associated with lower all-cause mortality, suggests a new study in a representative sample of U.S. adults.

Researchers analyzed data for 4,840 participants in the National Health and Nutrition Examination Survey who wore an accelerometer for an average of 5.7 days and 14.4 hours per day from 2003-2006, then were followed for a mean of 10.1 years. The average age was 56.8 years; 2,435 (54%) were women and 1732 (36%) had obesity

Compared with taking 4,000 steps per day, taking 8,000 steps per day was associated with significantly lower all-cause mortality (HR, 0.49), as was taking 12,000 steps per day (HR, 0.35).

"It's well established that engaging in physical activity can improve an individual's health and reduce the likelihood of developing obesity, cardiovascular disease, diabetes type 2, and some cancers," said lead author Pedro Saint-Maurice of the National Cancer Institute's Division of Cancer Epidemiology and Genetics in Bethesda, Maryland, in an email. "Our study reinforces this evidence by describing the associations between steps and risk for mortality."

Study participants logged an average of 9,124 daily steps, researchers report in JAMA.

A total of 1,165 deaths over the follow-up period included 406 from cardiovascular disease and 283 from cancer.

Unadjusted incidence density for all-cause mortality per 1,000 person-years was 76.7 for the 655 individuals who took less than 4,000 steps per day; 21.4 for the 1,727 people who took 4,000 to 7,999 steps per day; 6.9 for the 1,539 who took 8,000 to 11,999 steps per day; and 4.8 for the 919 individuals who took at least 12,000 steps per day.

Greater step intensity (steps per minute) was not significantly associated with lower mortality after adjustment for total steps per day (highest vs. lowest quartile of peak 30-minute cadence: HR, 0.90 (95% CI, 0.65-1.27); P value for trend = .34).

In analyses of subgroups, the authors found that higher step counts were associated with lower all-cause death rates among both men and women; among both younger and older adults; and among white, black, and Mexican-American adults. In secondary outcomes of the study, higher step counts were also associated with lower rates of death from cardiovascular disease and cancer.

Data reported were observational and no causal inferences can be made, the authors caution. Death certificates also don't always reflect the correct cause of death, the study team notes. In addition, the accelerometers in the study didn't track certain exercise, like swimming or cycling, which could impact mortality.

"These devices usually underestimate step count, particularly at a slow walking pace," said Zeljko Pedisic of the Institute for Health and Sport at Victoria University in Melbourne, Australia.

"It may be, however, it was the opposite in the current study, as it found participants did on average 9,124 steps a day, which is quite a lot," Pedisic, who wasn't involved in the study, said by email. "The absolute estimates of step counts should, therefore, be taken with caution."

It's possible that step intensity wasn't related to mortality rate after accounting for step count because those added steps lead to beneficial changes in blood pressure, insulin levels, lipid profile, and inflammation that can influence the potential for people to develop chronic diseases, said Dr. I-Min Lee of the Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital in Boston.

"While we have many studies showing that physical activity is beneficial for health, there are few data on STEPS and health, particularly long-term health outcomes," Dr. Lee, who wasn't involved in the study, said by email. "An expert committee - the 2018 Physical Activity Guidelines Advisory Committee, which reviewed the scientific evidence to support the current Physical Activity Guidelines for Americans, 2nd edition – noted this to be a critical gap in knowledge, since many individuals may be using wearables and monitoring their step counts."

Even so, the take-home message here is that any walking is better than nothing, said Keith Diaz, an assistant professor of behavioral medicine at Columbia University Medical Center in New York City.

"There is no threshold to reap the health benefits of walking," Diaz, who wasn't involved in the study, said by email. "With even small amounts of walking, your risk of death will be sharply reduced, and any pace of walking, no matter how fast or slow, will provide health benefit."

SOURCE: https://bit.ly/2QFyA3O JAMA, online March 24, 2020.

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