To date, only a handful of studies conducted outside of the United States have investigated the association between mortality and objectively measured step volume as determined by pedometer or accelerometer.2-4 While these studies observed that higher step counts are associated with lower mortality rates during follow-up periods of 5 to 10 years, their sample sizes were smaller and the study populations were different from those included in the study reported by Lee and colleagues. For example, the cohort from the United Kingdom included only men,2 and the participants in the Australian study were considerably younger, with a mean age of 59 years.4 In the current study, the largest of its kind thus far, it was observed that older women in the United States who take about 4400 steps a day have a lower mortality rate compared to those who take about 2700 steps a day. Moreover, the benefit of increased step volume on mortality progressively increases until plateauing at about 7500 steps per day. On the other hand, stepping intensity does not appear to lower mortality when step volume is accounted for. These results are important in that they add novel evidence that in older women, a patient population that tends to be sedentary, increased step volume (steps per day) but not stepping intensity (how quickly steps are taken) is associated with a reduction in mortality. Thus, these findings help to better characterize steps as a metric of ambulation in sedentary older adults per DHHS-PAG and add to the evidence necessary to translate this line of research into public health recommendations and programs.
While the health benefit of regular physical activity is well known and has been brought to the foreground with DDHA-PAG, only a small percentage of older adults engage in the recommended amounts and types of exercises. In other words, finding motivation to exercise is hard. Thus, identifying practical methods to facilitate behavioral change that increase and sustain physical activity in sedentary older adults would be essential to promoting health in this population. The use of wearable technologies such as fitness trackers and smartphone apps, devices that are now widely used, has shown promise for measuring and encouraging physical activity. The study by Lee and colleagues adds to this notion and further highlights the potential significance of step volume and mortality benefits in older women. Thus, future research in fitness technology should aim to integrate behavior change techniques (such as goal setting, feedback rewards, and action planning) and physical activity levels in order to improve health outcomes in older adults.5
In this study, the large sample size (> 16,000 participants), high compliance rate of accelerometer use (96% compliance rate), and reliable and continuous data capture (a built-in device feature) provide a large and complete dataset. This dataset, a major strength of the study, allowed the investigators to adequately control for potential confounders of physical activity, such as history of smoking, alcohol use, diet, and self-rated health, and therefore statistically minimize biases that are common in observational studies. However, some limitations inherent to the observational design are noted in this study. For instance, the observed association between step volume and mortality is correlational rather than causal, and a one-time assessment of steps taken over 7 consecutive days (ie, exposure) may not accurately reflect step volume and intensity of study participants over the span of 4.3 years of follow-up. Also, participants of WHS are predominately white, have higher socioeconomic status, and are more physically active than a national sample in the United States; therefore, caution should be exercised when making inferences to the general population.
Applications for Clinical Practice
Increased steps taken each day, up to about 7500 steps per day, is associated with lower mortality in older women. This finding can help inform the discussion when clinicians offer physical activity recommendations to older sedentary patients.
—Fred Ko, MD