Step By Step: Association Of Device-measured Daily Steps With All-cause Mortality - A Prospective Cohort Study

Abstract

Walking - a basic unit of locomotion - is free, does not require special training, and can be done almost everywhere. Therefore, walking might be a feasible behavior on which to tailor public health messages. There is however insufficient evidence available to determine the magnitude and shape of the relationship between steps taken per day and all-cause mortality, giving current step-based guidelines limited scientific basis. PURPOSE: To assess the prospective association and dose-response relationship between device-measured daily walking steps and all-cause mortality in a large population-based cohort of women and men aged 40-85 years. METHODS: Daily steps were measured by a waist-mounted accelerometer in 2,180 individuals (53% women) for seven consecutive days at baseline (2008-09). Participants were grouped into quarters (Q) based on their average number of steps per day and followed over a median period of 9.1 years for all-cause mortality determined by linkage with death certificates from the Norwegian Cause of Death Registry. RESULTS: Mean (SD) baseline age was 56 (11) years. Median (IQR) steps per day were 4651 (3495, 5325), 6862 (6388, 7350), 8670 (8215, 9186), and 11467 (10556, 13110) in Q1 to Q4, respectively. During follow-up, 119 individuals died (68% men). Higher number of steps per day was associated with lower risk of all-cause mortality with hazard ratios (95% CI) of 0.52 (0.29 to 0.93), 0.50 (0.27 to 0.94), and 0.43 (0.21 to 0.88) across ascending quarters of steps per day compared with Q1 (referent) in the multivariable model (p<0.001). The dose-response association modelled using restricted cubic splines demonstrated a non-linear, inverse association between daily steps taken and all-cause mortality, with no apparent plateauing of risk-reduction within the observed variation in the exposure. CONCLUSIONS:We observed a 48% risk reduction for all-cause mortality between the least active and the second quartile, with an absolute difference between Q1 and Q2 of 2200 steps per day. To exemplify, given an average stride length of 0.67 cm for women and 0.76 cm for men, 2200 steps translates to a 1.4 to 1.6 km walk for women and men, respectively. If confirmed, this large gain with modest effort may serve as encouragement to many sedentary individuals.