Borja del Pozo Cruz, PhD; Matthew N. Ahmadi, PhD; I-Min Lee, MBBS, ScD; et al
Key Points
- Every 2,000 steps reduces risk of premature death incrementally by 8 to 11 percent, up to approximately 10,000 steps a day.
- A higher number of steps per day was associated with a lower risk of all-cause dementia
- 9,800 steps was the optimal dose linked to lower risk of dementia by 50 percent, however risk was reduced by 25 percent at as low as 3,800 steps a day
- Stepping intensity or a faster pace showed beneficial associations for all outcomes (dementia, heart disease, cancer and death) over and above total daily steps.
Introduction
Evidence to date has prompted many to advocate for increasing daily steps as an important part of preventing chronic disease and premature mortality. Although this is popular advice, evidence to support the target of 10,000 steps per day for better health is scant. When Lee and colleagues found that as few as 4400 steps per day were associated with reduced mortality among older women, the finding led to debate and a call for more comprehensive evidence to inform step-based recommendations. Recent studies have suggested there is little additional risk reduction for all-cause mortality for more than 6000 to 8000 daily steps for those 60 years and older and 8000 to 10,000 steps for those younger than 60 years.
More steps have been associated with lower cardiovascular disease (CVD) mortality, but previous evidence is limited to older adults, high-risk populations, men only, women only, or cohorts with few mortality events, hindering the generalizability of the findings. More steps may lower the risks of cancer mortality, but evidence comes from only 1 study. Previous studies have missed the opportunity to explore beyond total daily steps to more specific step-based exposures (eg, differentiating between incidental vs purposeful steps). A more detailed analysis may be relevant for informing step-based recommendations. Moreover, the dose-response association between daily step counts and cancer incidence and CVD remain less explored. The intensity of the steps performed may also be relevant; however, current evidence is scarce, conflicting, and limited to mortality outcomes only. Besides, most evidence on step counts and intensity to date has relied on small cohort studies, which can make assessment of associations difficult, particularly for less common events.
This study examined the associations of daily step counts and step intensity with cancer and CVD incidence and all-cause, cancer-, and CVD-related mortality among a large sample of UK adults who wore wrist accelerometers.
Discussion
This large-scale accelerometry study of 78,500 adults from age 40 to 79 years contributes additional data on the associations of daily amounts and intensity of walking with mortality and incident disease. These findings are relevant for public health. We found no minimal threshold for the association of daily steps with mortality and morbidity. These associations were observed for up to approximately 10,000 steps per day, a threshold above which the level of statistical uncertainty may have blurred the true dose-response relationship. Similar patterns were observed for cancer and CVD incidence. Incidental steps were also associated with lower risk of mortality and morbidity. Nevertheless, purposeful steps and particularly peak-30 cadence were consistently associated with lower risk of all-cause mortality and cancer and CVD morbidity and mortality in this study.
All-Cause, Cancer, and CVD Mortality
We found evidence of an inverse dose-response association between daily steps and all-cause, cancer, and CVD mortality up to approximately 10,000 steps per day, a threshold that is 20% higher than previously observed in participants age 60 years and older but similar to that seen in younger participants. Most existing consumer-grade activity trackers are wrist-worn, and our data may represent more relevant targets for the population compared with previous studies. These study results highlight the potential value of higher amounts of daily steps (ie, ~10,000 steps per day; absolute risk reduction, 36% vs baseline level) for optimal health; however, the proportion of the population currently achieving this goal is low (~20% in this sample). We did not find a minimal threshold for the beneficial association between stepping and mortality risk in this sample. Other studies have reported similar findings. Promotion of lower step targets may provide a more realistic and achievable goal for the general adult population where longevity gains may be maximized simply by shifting away from the least-active end of the step-count distribution. Peak-30 cadence was consistently associated with lower mortality risks (absolute risk reduction difference between extreme quintiles, 34%), a finding that reflects the importance of the natural best effort relative to the individual’s capability and may better represent the amount of activity at higher intensities than other metrics.
Cancer and CVD Incidence
Previous cross-sectional evidence has shown a correlation between increased walking and a lower risk of CVD prevalence. We provide novel evidence of a prospective association of step counts with CVD mortality and incidence. Previous randomized clinical trials have shown the robust effects of walking on several CVD risk factors. We identified similar data patterns for cancer incidence. Notably, we detected an association between incidental steps and a lower risk of both cancer and CVD incidence. This finding warrants further attention because incidental walking throughout the day may be more feasible for some people and may be associated with additional health benefits, more so than purposeful steps. Similarly, peak-30 cadence was inversely and consistently associated with cancer and CVD incidence. Our study contributes critical evidence toward step count−based recommendations, which could be particularly easy to communicate, interpret, and measure. Step counts may be especially relevant for people who mostly perform incidental, unstructured, and unplanned physical activity. For individuals who are not intentionally tracking their physical activity, it may be challenging to recall time-based physical activity amounts or determine whether they are sufficiently active in relation to the current minute- and intensity-based guidelines. Therefore, step-based guidelines could provide useful supplementary recommendations to the current physical activity guidelines.
Strengths and Limitations
This study had several strengths. First, to our knowledge, this was the largest population sample and analysis of adults using accelerometry and linkage to prospective outcomes. The device and protocol used allowed us to collect 24 h of accelerometry data to reduce the chance of missing periods of ambulatory activity. We used registry-based prospectively collected data, which increased the internal validity of our estimates. Unlike previous studies, we accounted for the presence of competing risks for event-specific outcomes. We also took measures to minimize the likelihood of reverse causation by censoring all the events that occurred during the first 2 years of follow-up. Lastly, the machine learning algorithm we used allowed us to separate walking steps from other ambulatory activity, thus overcoming some common limitations of previous studies.
This study also had limitations. First, the observational design of this study precludes us from making causal claims. Second, the step-count data were collected only once at baseline and may not be representative of habitual walking behavior. Nevertheless, we found consistent daily steps in participants with available repeated accelerometer wear approximately 4 years later (n = 3400; intraclass correlation, 0.76). Third, despite censoring participants who had the event of interest within the first 2 years of follow-up, some potential for reverse causation may still exist. Fourth, although a priori defined directed acyclic graph was used to identify key factors known to influence the causal associations between steps and mortality and disease incidence outcomes, residual or unmeasured confounding may still be present. Fifth, covariates were not measured at accelerometer wear date. Nonetheless, responses to the selected covariates were relatively stable over time, and therefore, the associations between accelerometer-assessed physical activity and health outcomes are valid. Sixth, the UK Biobank had a very low response rate (5.5% of those invited; 45% of UK Biobank participants for the accelerometry study; mortality rate, 6.1 and 4.1 per 1000 person-years, respectively) and participants were not representative of the overall UK population. However, recent studies have demonstrated that the lack of representativeness in the UK Biobank does not affect the associations of physical activity with disease incidence and mortality outcomes. The uptick of the right part of the dose-response curves in this study likely reflects the sparsity of data and/or events rather than a genuine lack of beneficial association at higher levels of stepping. This is particularly evident after approximately 10,000 steps per day, which may represent the health consciousness of the participants in the study around this target. Finally, because the relative energy cost of walking and other daily activities is higher in older adults than younger adults, the observed benefits of daily step counts may vary depending on the interaction between step intensity and age. Hence, a single recommendation for step count may not be appropriate for all adults; however, this interaction was not observed in our sample.
Conclusions
This population-based prospective cohort study using UK Biobank data for 78 500 individuals suggests that accruing more steps per day (up to ~10?000 steps/d) was associated with steady declines in mortality risks, beyond which the associations were less evident. There was no minimal threshold for the beneficial association of increasing the number of daily steps with mortality and morbidity. If combined with effective behavioral strategies, this information could be used to motivate the least active individuals to increase their steps and the more active individuals to reach the 10,000-step target. Daily steps were also associated with cancer and CVD incidence. Peak-30 cadence was consistently associated with morbidity and mortality. These findings can inform future evidence-based physical activity recommendations using daily steps.
