Association of Daily Step Count and Step Intensity With Mortality Among US Adults.
Level 3 - non-randomized controlled study
Prospective cohort study with objective baseline exposure measurement and long-term mortality follow-up
PubMed 32207799 · doi:10.1001/jama.2020.1382
What was done
Researchers evaluated a representative sample of 4,840 US adults aged 40 years or older from the National Health and Nutrition Examination Survey (NHANES 2003–2006). Physical activity was objectively tracked via an accelerometer worn at baseline for up to 7 days (mean 5.7 days, 14.4 hours/day). The study assessed the association between daily step count, step intensity (extended bout cadence, peak 30-minute cadence, and peak 1-minute cadence), and mortality through December 2015 (mean follow-up: 10.1 years). Multivariable models adjusted for age, sex, race/ethnicity, education, diet, smoking, BMI, self-reported health, mobility limitations, and major chronic comorbidities.
What was found
Over follow-up, 1,165 deaths occurred (406 CVD deaths, 283 cancer deaths). Mean baseline daily steps were 9,124. Unadjusted all-cause mortality rates were: 76.7 per 1,000 person-years (419 deaths) for <4,000 steps/day (n = 655); 21.4 per 1,000 person-years (488 deaths) for 4,000–7,999 steps/day (n = 1,727); 6.9 per 1,000 person-years (176 deaths) for 8,000–11,999 steps/day (n = 1,539); and 4.8 per 1,000 person-years (82 deaths) for ≥12,000 steps/day (n = 919). Compared with 4,000 steps/day, taking 8,000 steps/day was associated with lower all-cause mortality (adjusted HR 0.49; 95% CI, 0.44–0.55), as was taking 12,000 steps/day (adjusted HR 0.35; 95% CI, 0.28–0.45). Greater step intensity was not significantly associated with lower mortality after adjusting for total steps per day (highest vs lowest quartile of peak 30 cadence: HR 0.90; 95% CI, 0.65–1.27; P for trend = .34).
Why it matters
This study demonstrates that total daily walking volume is strongly linked to reduced mortality risk, while stepping cadence or intensity offers minimal additional survival benefit once total daily volume is accounted for.
Limits
Physical activity was measured only during a single 7-day period at baseline, which may not capture long-term activity changes over the 10-year follow-up. The observational design cannot rule out residual confounding or reverse causation from preclinical illness. The cohort was restricted to US adults aged 40 and older.
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