Reference: JAMA Netw Open. 2023 Mar 1;6(3):e235174
Practice Point: One to 2 days per week of walking at least 8,000 steps per day might be enough to decrease all-cause mortality.
EBM Pearl: Hazard ratios are more appropriate than adjusted risk differences (aRDs) when analyzing time-dependent observational data.
Getting people to exercise is a challenge. Common sense dictates that any exercise is better than none, but does the weekend warrior approach work? We still don’t have good evidence on how many days per week one must walk to optimize long-term health. To that point, a recent study in JAMA looked at the association between days/week walked and all-cause mortality risk at 10 years.
Researchers linked 2005/2006 NHANES data to the National Death Index through 2019 for 3,101 adult participants who wore an accelerometer for at least 4 days during the study period. Participants were categorized into groups based on the number of days (0, 1-2, and 3-7) they achieved ≥ 8,000 steps during the 1 week of accelerometer data collection and were evaluated for all-cause and CVD mortality. (That’s correct — this whole study examining 10-year mortality trends is based on 1 week of self-reported data.) The dose-response association was also examined for the number of days/week participants achieved 8,000 steps and mortality.
At 10 years, all-cause mortality risk was significantly lower among those who took ≥ 8,000 steps 1 to 2 days per week (adjusted risk difference [aRD] = -14.9%) and 3 to 7 days per week (aRD = -16.5%) on the absolute scale, compared with 0 days per week. Similarly, CVD mortality risk was 8.1% lower among those who took ≥ 8,000 steps 1 to 2 days a week and 8.4% lower in participants who took the steps 3 to 7 days. The relationship between walking frequency and mortality risk followed a curvilinear pattern, with a rapid decrease in risk up to 3 to 4 days of walking per week, after which the risk plateaued.
So do we think walking 8,000 steps 1 or 2 days per week is sufficient to tack on a few extra years to your life? Maybe, but not necessarily based on this study due to a few important problems. The first is “the chicken and the egg” conundrum: when we observe a population, those who exercise are already healthier and more likely to live longer. This was not a randomized trial, and the initial observation was effectively looking at 3 different populations. Participants with a higher frequency of > 8,000-step-days at the beginning of the study tended to be younger, nonsmokers, less likely to have obesity or other medical conditions, and/or rate their health well, all factors known to be associated with better long-term health independent of activity level. Secondly, aRDs simply aren’t the appropriate statistical tool to use here: HR’s would have been better since they account for time-to-event, whereas aRDs quantify the absolute disparity in risk between the exposed and unexposed groups.
We all know that correlation does not equal causation. These 3 groups seem to be fundamentally different which makes them hard to compare. It’s also hard to say that 1 week of data is truly a reflection of step counts over the next 10 years. All that being said, there is likely little harm in recommending that our patients strive to get at least 8,000 steps once weekly. And citing this study to our patients might be a good sell to help get them moving.
For more information, see the topic Adult Preventative Health in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Elham Razmpoosh, PhD, Postdoctoral fellow at McMaster University. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School; Katharine DeGeorge, MD, MS, Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia; Dan Randall, MD, Deputy Editor at DynaMed; Nicole Jensen, MD, Family Physician at WholeHealth Medical; Vincent Lemaitre, PhD, Senior Medical Writer at DynaMed; and Sarah Hill, MSc, Associate Editor at DynaMed.