By Michael H. Crawford, MD, Professor of Medicine, Lucy Stern Chair in Cardiology, University of California, San Francisco
Considerable attention has been paid to daily step counts (SC) as a device to encourage walking and reduce the risk of cardiovascular events (CVEs). However, minimal or optimal levels of SC have not been well characterized, and the influence of walking intensity, sex, and the SC device have not been fully elucidated.
Stens et al performed a meta-analysis and systematic review of available studies online since the inception of online storage that quantitated steps, evaluated the association of SC with CVE, used prospective cohorts of adults without CV disease (CVD) at baseline, were peer reviewed, and in English. The authors performed categorical and dose response analyses. They measured step cadence as the peak 30-minute cadence divided into low, intermediate, and high categories. Researchers also examined device type and wear location. Stens et al studied continuous dose response in increments of 500 steps per day (Sd), with a reference level of 2,000 Sd.1
After systematically reviewing 29 potential study papers, the authors selected 12 for inclusion (11 assessed SC and all-cause mortality, four assessed incident CVD, four assessed step cadence and all-cause mortality, and one assessed SC and cardiac hospitalization). The resulting analytical cohort was 111,309 individuals (median age was 63 years, 61% were women, and median body mass index was 27 kg/m2).
Pedometers were used in three studies and accelerometers were used in nine studies (eight hip, one wrist). All but one study collected SC for seven days. Most study authors corrected for known clinical confounders and used national death registry data. Over a median follow-up of 78 months, 4.4% died. Over 73 months, 1.4% experienced a CVE.
The continuous dose response analysis showed that at 2,517 Sd, all-cause mortality rates were significantly lower vs. the reference level of 2,000 Sd (adjusted hazard ratio [aHR], 0.92; 95% confidence interval [CI], 0.84-0.99), as was CVE (aHR, 0.89; 95% CI, 0.79-0.99). A higher SC displayed a non-linear risk reduction for all-cause mortality at an optimal count of 8,763 Sd (aHR, 0.40; 95% CI, 0.38-0.43) and for CVE at an optimal count of 7,126 (aHR, 0.49; 95% CI, 0.45-0.55). Speeding step cadence from low to intermediate or high also was associated with lower all-cause mortality rates. Sex did not influence these associations, but device location and type did. Hip-worn accelerometer data were strongly associated with reductions in all-cause mortality rates, whereas wrist-worn accelerometers and pedometers were not.
The authors concluded mortality and CVE rates were reduced significantly with as few as 2,600 Sd to 2,800 Sd, and this effect peaked at about 7,200 Sd to 8,800 Sd. Researchers observed additional mortality benefit at intermediate to high step cadence.
Commentary
Although I have never been a big fan of meta-analyses, some hypotheses are unlikely to ever be tested in a randomized controlled trial. Daily step counts and their relationship to mortality and CVE is such a topic. Several smaller studies have called into question the 10,000 Sd to achieve cardiovascular health benefits. Interestingly, this number was totally made up by a Japanese company that made pedometers, with no science behind it.2
The strengths of the Stens et al study were the selection of observational cohort studies with low bias that modeled a continuous dose response. This resulted in a huge study population of middle-aged adults of both sexes, many of whom were overweight. This is exactly the population physicians are trying to motivate to exercise more.
Weaknesses included the fact SC was measured only at baseline. Therefore, investigators could not assess changes in exercise activities over time. Also, there was no assessment of the factors that influence physical activity. Only four studies in this meta-analysis were evaluations of step cadence. The results of this study also probably do not apply to older subjects with chronic diseases or low-income individuals.
The major message of the Stens et al study is SC well below 10,000 per day produce significant reductions in mortality and CVE. Using those who walked 2,000 Sd as a comparator, only about 600 more steps a day resulted in an 8% reduction in mortality rates and an 11% decrease in CVE rates. Since there are roughly 2,000 steps to a mile, this represents going an additional quarter mile. Also, the curvilinear dose response curve flattened at about 8,000 Sd, or four miles, which produced a 60% reduction in mortality rates and a 51% reduction in CVE rates vs. walking one mile. Increasing walking cadence added another 20% reduction in adverse CV outcomes. This is a simple public health message that is easy to understand and may not require much more exercise for many since significant benefits were obtained with far fewer than 10,000 Sd. Another plus is the fact that if a patient owns a mobile phone with an accelerometer in it and wears it on their hip, then patients do not have to buy a pedometer, a smartwatch, or other wrist-worn step counters.
REFERENCES
- Stens NA, Bakker EA, Mañas A. Relationship of daily step counts to all-cause mortality and cardiovascular events. J Am Coll Cardiol 2023;82:1483-1494.
- Lee IM, Shiroma EJ, Kamada M, et al. Association of step volume and intensity with all-cause mortality in older women. JAMA Intern Med 2019;179:1105-111
Considerable attention has been paid to daily step counts (SC) as a device to encourage walking and reduce the risk of cardiovascular events. However, minimal or optimal levels of SC have not been well characterized, and the influence of walking intensity, sex, and the SC device have not been fully elucidated.
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