Association of Daily Step Count and Step Intensity With Mortality
Are the number of steps per day and the intensity of stepping associated with lower mortality?
A representative sample of US adults aged ≥40 years in the National Health and Nutrition Examination Survey (NHANES) wore an accelerometer for up to 7 days during 2003-2006. Accelerometer data were based on measurements obtained during a 7-day period at baseline; and included number of steps per day, and three measures of step intensity (extended bout cadence, peak 30-minute cadence, and peak 1-minute cadence [steps/minute]). The primary outcome was all-cause mortality ascertained through December 2015; secondary outcomes were cardiovascular disease (CVD) and cancer mortality. Hazard ratios (HRs), mortality rates, and 95% confidence intervals (CIs) were estimated using cubic splines and quartile classifications adjusting for age; sex; race/ethnicity; education; diet; smoking status; body mass index; self-reported health; mobility limitations; and diagnoses of diabetes, stroke, heart disease, heart failure, cancer, chronic bronchitis, and emphysema.
A total of 4,840 participants (mean age 56.8 years; 2,435 [54%] women; 1,732 [36%] individuals with obesity) wore accelerometers for a mean of 5.7 days for a mean of 14.4 hours per day. The mean number of steps per day was 9,124. There were 1,165 deaths over a mean 10.1 years of follow-up, including 406 CVD and 283 cancer deaths. The unadjusted incidence density for all-cause mortality was 76.7 per 1,000 person-years (419 deaths) for the 655 individuals who took <4,000 steps per day; 21.4 per 1,000 person-years (488 deaths) for the 1,727 individuals who took 4,000-7,999 steps per day; 6.9 per 1,000 person-years (176 deaths) for the 1,539 individuals who took 8,000-11,999 steps per day; and 4.8 per 1,000 person-years (82 deaths) for the 919 individuals who took ≥12,000 steps per day. Compared with taking 4,000 steps per day, taking 8,000 steps per day was associated with significantly lower all-cause mortality (hazard ratio [HR], 0.49; 95% CI, 0.44-0.55), as was taking 12,000 steps per day (HR, 0.35; 95% CI, 0.28-0.45). Unadjusted incidence density for all-cause mortality by peak 30 cadence was 32.9 per 1,000 person-years (406 deaths) for the 1,080 individuals who took 18.5-56.0 steps per minute; 12.6 per 1,000 person-years (207 deaths) for the 1,153 individuals who took 56.1-69.2 steps per minute; 6.8 per 1,000 person-years (124 deaths) for the 1,074 individuals who took 69.3-82.8 steps per minute; and 5.3 per 1,000 person-years (108 deaths) for the 1,037 individuals who took 82.9-149.5 steps per minute. Greater step intensity was not significantly associated with lower mortality after adjustment for total steps per day (highest vs. lowest quartile of peak 30 cadence (HR, 0.90; 95% CI, 0.65-1.27; p value for trend = 0.34).
Based on a representative sample of US adults, a greater number of daily steps was significantly associated with lower all-cause mortality. After adjusting for total steps per day, there was no significant association between step intensity and mortality.
Previous studies reporting higher step counts associated with lower mortality were conducted in older adults, in smaller cohorts with relatively few deaths, and in patients with heart failure or chronic lung disease. Data associating gait speed or walking pace with lower mortality have been mixed. This study employed data from the NHANES, a representative sample of noninstitutionalized US adults from 2003 to 2006, in which participants were asked to wear an accelerometer on the hip during waking hours for a 7-day period. It revealed a dose-dependent association between greater number of steps per day and reduction in all-cause, cardiovascular, and cancer mortality; but, after adjusting for total steps per day, no significant association between step intensity and mortality. Although the study was observational and a causal relationship cannot be confirmed, this study provides additional data to support that even low-level physical activity is an important modifier of mortality risk.
Keywords: Cardiovascular Diseases, Gait, Heart Failure, Lung Diseases, Mortality, Neoplasms, Obesity, Physical Fitness, Primary Prevention, Walking
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