Lee I, Shiroma E, Evenson K, Kamada M, LaCroix A, and Buring J. Accelerometer-measured physical activity and sedentary behavior in relation to all-cause mortality: The Women’s Health Study. Circulation. 2018;137:203-205.
To evaluate the association between type and quantity of physical activity and longevity in women.
Prospective cohort study
The study enrolled 17,708 women (mean age 72, standard deviation 5.7 years) recruited from the Women’s Health Study (WHS); all enrolled women were able to walk outside the home unassisted. Participants were given a triaxial accelerometer (ActiGraph GT3X+) to wear for 7 days, with a minimum requirement of wearing it at least 10 hours per day on at least 4 days. After excluding for failed devices and noncompliance with usage, data from 16,741 women was analyzed.
Study Parameters Assessed
Using data from the ActiGraph GT3X+, investigators calculated the total volume of physical activity in minutes per day. Activity was divided into categories based on accelerometer counts per minute: sedentary at less than 200 counts per minute, light physical activity (LPA) between 200 and 2,689 counts per minute, and moderate- to vigorous-intensity physical activity (MVPA) at 2,690 counts per minute or more. Participants were stratified into quartiles based on minutes per day of total physical activity, sedentary behavior, LPA, and MVPA.
This research is a reminder that small changes need to progress into at least moderate-intensity exercise to be truly beneficial to longevity.
Researchers also gathered information regarding smoking status, alcohol use, dietary composition, use of hormone therapy, personal history of cancer or cardiovascular disease, and family history of myocardial infarction or cancer via self-report and—when possible—medical records.
Data was analyzed using proportional hazards regression models.
Primary Outcome Measures
The primary outcome measure of the study was mortality, as determined by medical records, death certificates, or the National Death Index. Participants were enrolled between 2011 and 2015, and mortality was assessed through December 31, 2015. The average follow-up was 2.3 years.
Over the course of the study, 207 of the 16,741 women included in the study died. Two models were used to analyze the hazard ratios between activity and mortality: Model 1 adjusted for age and accelerometer wear time, and Model 2 adjusted for potential confounding factors related to lifestyle and personal and family health history.
Strong inverse associations were identified between total activity and mortality (P=0.002) and MVPA and mortality (P=0.0002) under analysis of both Model 1 and Model 2. The magnitude of risk reduction between the highest and lowest quartiles of activity was roughly 60% to 70%.
An inverse association was observed between LPA and mortality (P=0.04), but when adjusted for potential confounding factors in Model 2, the association was no longer statistically significant (P=0.82). Similarly, an association between sedentary behavior and increased mortality was noted (P=0.007), but when adjusted for confounding factors, statistical significance was lost (P=0.99).
The researchers concluded that physical activity is beneficial for longevity, and that this benefit is largely derived from MVPA.
This research adds to the body of evidence used to develop the physical activity guidelines released by the United States Office of Disease Prevention and Health Promotion (ODPHP). Until recently, the studies used to develop these guidelines relied on self-reporting of moderate and vigorous physical activity. The advent of activity-measuring devices allows for detection and analysis of the effects of lighter physical activity, as well as more accurate assessment of moderate and vigorous activity.
According to this research, exercise appears to help people live longer. While not exactly earth-shattering news, this data demonstrates a more dramatic magnitude of benefit than previous research that used a self-reporting model for activity (roughly 60%to 70% vs 30% to 40% risk reduction when comparing the most active individuals to the least active).1 It also suggests that light activity alone is not enough to get this benefit, affirming current guidelines published by the ODPHP and World Health Organization.2,3
Current physical activity guidelines recommend adults get at least 150 minutes of moderate-intensity exercise or 75 minutes of vigorous exercise per week, plus strength training exercises on 2 or more days per week. Intensity of exercise can be judged clinically using the Borg Rating of Perceived Exertion (RPE) scale or target heart rate zones.4,5 The Borg scale ranges from 0 (lying in bed) to 20 (sprinting as fast as possible); moderate intensity activity corresponds to 11-14 on the scale, and vigorous activity corresponds to 17-19 on the scale. In the heart zone model, moderate intensity exercise is 50% to 70% of maximum heart rate and vigorous exercise is 70% to 85% of maximum heart rate, where maximum heart rate is estimated as 220 minus the person’s age in years.
According to the 2016 National Health Interview Survey (NHIS), only 51.7% of adults in the United States get the recommended amount of aerobic exercise.6 Inactivity is a modifiable risk factor for chronic disease morbidity and mortality,1 and it is getting renewed attention in popular culture (such as with “sitting is the new smoking,” a phrase popularized by Dr. James Levine of the Mayo Clinic).7 As a healthcare provider, it can be challenging to motivate patients to exercise. Given the disappointing compliance with current guidelines, it seems a didactic approach is not effective for many individuals. Therefore, it is the responsibility of providers to adapt and develop alternative strategies for fostering lifestyle changes in those who do not respond to simply being told the current guidelines.
In natural medicine, longer visits and the stronger rapport they can foster provide a unique advantage in encouraging lifestyle improvements. The specific benefits of physical activity for the individual can be discussed in detail, obstacles to change can be teased out, personalized motivations for becoming more active can be elicited, favorite physical activities can be identified, and goals can be developed collaboratively. For some patients, baby steps will be needed. However, this research is a reminder that small changes need to progress into at least moderate-intensity exercise to be truly beneficial to longevity. So make that walk a brisk one.
This study was strengthened by its large sample size and adjustments for confounding factors. Potential limitations include short follow-up time that cannot exclude reverse causation, as well as reliance on self-reporting for confounding factors. The authors’ choice not to make the details of their research available for reproducing results or replicating procedures is confusing; however, the noncontroversial nature of the results makes in-depth scrutiny of their research methods less necessary.