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Abstract
Background Despite accumulating evidence concerning the association between daily step counts and mortality or disease risks, it is unclear whether daily step counts are associated with healthy life years.
Methods We used the combined dataset of the Comprehensive Survey of Living Conditions and the National Health and Nutrition Survey conducted for a randomly sampled general population in Japan, 2019. Daily step counts were measured for 4957 adult participants. The associations of daily step counts with activity limitations in daily living and self-assessed health were evaluated using a multivariable logistic regression model. The bootstrap method was employed to mitigate uncertainties in estimating the threshold of daily step counts.
Results The median age was 60 (44–71) years, and 2592 (52.3%) were female. The median daily step counts were 5650 (3332–8452). The adjusted OR of activity limitations in daily living for the adjacent daily step counts was 0.27 (95% CI 0.26 to 0.27) for all ages and 0.25 (95% CI 0.25 to 0.26) for older adults at the lowest, with the thresholds of significant association at 9000 step counts. The OR of self-assessed unhealthy status was 0.45 (95% CI 0.44 to 0.46) for all ages and 0.42 (95% CI 0.41 to 0.43) for older adults at the lowest, with the thresholds at 11 000 step counts.
Conclusion Daily step counts were significantly associated with activity limitations in daily living and self-assessed health as determinants of healthy life years, up to 9000 and 11 000 step counts, respectively. These results suggest a target of daily step counts to prolong healthy life years within health initiatives.
Introduction
Healthy life years, also known as healthy life expectancy, are holistic health indicator encompassing life, health, disease, disability, activity limitation and overall well-being. Estimations of healthy life years are derived from national health surveys that incorporate questionnaires to assess the presence of activity limitations in daily living and self-assessed health in the USA and the UK as well as Japan.1–3 In addition to conventional risk factors of lifestyle-related diseases,4 5 several non-fatal conditions, such as mental health diseases, orthopaedic problems and neurological disorders, substantially influence healthy life years.6–8 Effective health policies for the disease prevention and health promotion are necessary to prolong healthy life years and narrow the differences between life expectancy and healthy life years.
Physical activities and exercises are expected to be beneficial for healthy life years.9–11 Walking is a cost-effective aerobic physical activity in daily life, and its metric, step count, is readily measured by simple devices. While the WHO has issued guidelines recommending regular physical activity to promote a healthy life, it has refrained from specifying the optimal target of daily step counts.12 Notably, an increase in daily step counts ameliorates cardiovascular disease (CVD) and mortality risk.13–15 In this context, target step counts of 7200 and 8800 per day have been suggested for mitigating the risk of CVD and all-cause mortality, respectively.16
Despite accumulating evidence concerning the association between daily step counts and mortality or disease risks, there is limited knowledge regarding the association between daily step counts and healthy life years. The purpose of this study is to elucidate the associations of daily step counts with activity limitations in daily living and self-assessed health, as key determinants of healthy life years, and provide the optimal target of daily step counts to prolong healthy life years.
Discussion
This study using the combined national health survey data has provided the insights into the associations of daily step counts with activity limitations in daily living and self-assessed health, as key determinants of healthy life years. An increase in daily step counts was significantly associated with the improvement of activity limitations in daily living and self-assessed health, with thresholds of significant association at 9000 and 11 000 step counts, respectively, regardless of age.
This study suggests the optimal target of daily step counts to prolong healthy life: 9000 step counts for activity limitations in daily living and 11 000 step counts for self-assessed health. Increase in daily step counts reduces CVD and mortality risks, whereas the effect of step intensity is controversial.13–15 20 21 A meta-analysis has introduced 7200 and 8800 step counts per day as potential targets for reducing CVD and all-cause mortality risks, respectively.16 Given that healthy life years are shorter than life expectancy, it is conceivable that the optimal targets of daily step counts, for prolonging healthy life years, may necessitate more step counts than what are required for the reduction of mortality and CVD risk.
We evaluated activity limitations in daily living and self-assessed health status—metrics that do not include mortality, as alternatives to healthy life years. Indeed, healthy life years are estimated based on a health survey regarding activity limitations in daily living and self-assessed health in the USA and the UK as well as Japan.1–3 The prevalence rates of activity limitations in daily living or self-assessed unhealthy status in each age groups are incorporated into a life table to estimate healthy life years.22 Self-assessed health has been shown to be a predictor for mortality and morbidity.23 24 In addition, racial and ethnic disparities of self-assessed health status have been reported.25 While life expectancy has been increasing, healthy life years have not kept pace in the world.26 27 An improvement of activity limitations in daily living and self-assessed health by an effective health promotion, such as an increase in daily step counts in the general population, will prolong healthy life years, and narrow the existing health disparities.
The data used in this study are derived from national cross-sectional surveys, and no causal inferences can be deduced. Population-based cohort will be needed to further investigate the prospective effect of daily step counts on healthy life years. Step intensity was not evaluated because the investigation did not include it. Potential confounding factors, such as income, that could affect the association between daily step counts and healthy life years were not considered.
Conclusion
Daily step counts were significantly associated with activity limitations in daily living and self-assessed health as determinants of healthy life years, up to 9000 and 11 000 step counts, respectively. These findings suggest the optimal target of daily step counts to prolong healthy life years within health initiatives aimed at increasing physical activity and raising health awareness of people.
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