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Study Overview
Objective. To evaluate the association of number of steps taken per day and stepping intensity with all-cause mortality in older women.
Design. This was a prospective cohort study of US women participating in the Women’s Health Study (WHS). Participants wore an accelerometer device (ActiGraph GT3X+, ActiGraph Corp, Pensacola, FL) on the hip during waking hours for 7 consecutive days between 2011 and 2015. The accelerator data were collected at 30 Hz and aggregated into 60-second, time-stamped epochs. Data from participants who were adherent with wearing devices (defined as ≥ 10 hours/day of wear on ≥ 4 days) were used in an analysis that was conducted between 2018 and 2019. The exposure variables were defined as steps taken per day and measures of stepping intensity (ie, peak 1-minute cadence; peak 30-minute cadence; maximum 5-minute cadence; and time spent at a stepping rate of ≥ 40 steps/minute, reflecting purposeful steps).
Setting and participants. In total, 18,289 women participated in this study. Of these, 17,708 wore and returned their accelerometer devices, and data were downloaded successfully from 17,466 devices. Compliant wearers of the device (≥ 10 hours/day of wear on ≥4 days) included 16,741 participants (96% compliance rate of all downloaded device data).
Main outcome measure. All-cause mortality as ascertained through the National Death Index or confirmed by medical records and death certificates.
Main results. In this cohort of 16,741 women, average age at baseline was 72.0 ± 5.7 years (range, 62 to 101 years) and the mean step count was 5499 per day (median, 5094 steps/day) during the 7-day data capture period between 2011 and 2015. Not taking steps (0 steps/minute) accounted for 51.4% of the recorded time, incidental steps (1 to 39 steps/minute) accounted for 45.5%, and purposeful steps (≥ 40 steps/minute) accounted for 3.1%. The mean follow-up period was 4.3 years; during this time, 504 participants died. The median steps per day across quartiles were 2718 (lowest), 4363, 5905, and 8442 (highest). The corresponding quartile hazard ratios (HRs) associated with mortality adjusted for confounders were 1.00 (reference; lowest quartile), 0.59 (95% confidence interval [CI], 0.47-0.75), 0.54 (95% CI, 0.41-0.72), and 0.42 (95% CI, 0.30-0.60; highest quartile), respectively (P < 0.01). A higher mean step count per day, up to approximately 7500 steps/day, corresponded with progressive and steady decline in mortality HRs using spline analyses. Similar results were observed using sensitivity analyses that minimized reverse causation bias. While the adjusted analysis of measures of stepping intensity showed an inverse association with mortality rates, these associations were no longer significant after accounting for steps per day. Specifically, adjusted HRs comparing highest to lowest quartile were 0.87 (95% CI, 0.68-1.11) for peak 1-minute cadence; 0.86 (95% CI, 0.65-1.13) for peak 30-minute cadence; 0.80 (95% CI, 0.62-1.05) for maximum 5-minute cadence; and 1.27 (95% CI, 0.96-1.68) for time spent at a stepping rate of ≥ 40 steps/minute.
Conclusion. Older women who took approximately 4400 steps per day had lower all-cause mortality rates during a follow-up period of 4.3 years compared to those who took approximately 2700 steps each day. Progressive reduction in mortality rates was associated with increased steps per day before leveling at about 7500 steps/day. Stepping intensity, when accounting for number of steps taken per day, was not associated with reduction in mortality rates in older women.
Commentary
The health and mortality benefits of exercise are well recognized. The 2018 Department of Health and Human Services Physical Activity Guidelines (DHHS-PAG) recommend that adults should do at least 150 to 300 minutes of moderate-intensity aerobic physical activity per week, or 75 to 150 minutes of vigorous-intensity aerobic physical activity per week, in addition to doing muscle-strengthening activities on 2 or more days a week.1 Importantly, the guidelines emphasize that moving more and sitting less benefit nearly everyone, and note that measures of steps as a metric of ambulation can further promote translation of research into public health recommendations for exercise interventions. Despite this recognition, there is limited information centering on the number of daily steps (step volume) and the intensity of stepping that are needed to achieve optimal health outcomes in older adults. The study reported by Lee and colleagues adds new knowledge regarding the relationship between step volume and intensity and mortality in older women.
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
1. Piercy KL, Troiano RP, Ballard RM, et al. The physical activity guidelines for Americans. JAMA. 2018;320:2020-2028.
2. Jefferis BJ, Parsons TJ, Sartini C, et al. Objectively measured physical activity, sedentary behaviour and all-cause mortality in older men: does volume of activity matter more than pattern of accumulation? Br J Sports Med. 2019;53:1013-1020.
3. Yamamoto N, Miyazaki H, Shimada M, et al. Daily step count and all-cause mortality in a sample of Japanese elderly people: a cohort study. BMC Public Health. 2018;18:540.
4. Dwyer T, Pezic A, Sun C, et al. Objectively measured daily steps and subsequent long term all-cause mortality: the Tasped prospective cohort study. PLoS One. 2015;10:e0141274.
5. Sullivan AN, Lachman ME. Behavior change with fitness technology in sedentary adults: a review of the evidence for increasing physical activity. Front Public Health. 2016;4:289.
Study Overview
Objective. To evaluate the association of number of steps taken per day and stepping intensity with all-cause mortality in older women.
Design. This was a prospective cohort study of US women participating in the Women’s Health Study (WHS). Participants wore an accelerometer device (ActiGraph GT3X+, ActiGraph Corp, Pensacola, FL) on the hip during waking hours for 7 consecutive days between 2011 and 2015. The accelerator data were collected at 30 Hz and aggregated into 60-second, time-stamped epochs. Data from participants who were adherent with wearing devices (defined as ≥ 10 hours/day of wear on ≥ 4 days) were used in an analysis that was conducted between 2018 and 2019. The exposure variables were defined as steps taken per day and measures of stepping intensity (ie, peak 1-minute cadence; peak 30-minute cadence; maximum 5-minute cadence; and time spent at a stepping rate of ≥ 40 steps/minute, reflecting purposeful steps).
Setting and participants. In total, 18,289 women participated in this study. Of these, 17,708 wore and returned their accelerometer devices, and data were downloaded successfully from 17,466 devices. Compliant wearers of the device (≥ 10 hours/day of wear on ≥4 days) included 16,741 participants (96% compliance rate of all downloaded device data).
Main outcome measure. All-cause mortality as ascertained through the National Death Index or confirmed by medical records and death certificates.
Main results. In this cohort of 16,741 women, average age at baseline was 72.0 ± 5.7 years (range, 62 to 101 years) and the mean step count was 5499 per day (median, 5094 steps/day) during the 7-day data capture period between 2011 and 2015. Not taking steps (0 steps/minute) accounted for 51.4% of the recorded time, incidental steps (1 to 39 steps/minute) accounted for 45.5%, and purposeful steps (≥ 40 steps/minute) accounted for 3.1%. The mean follow-up period was 4.3 years; during this time, 504 participants died. The median steps per day across quartiles were 2718 (lowest), 4363, 5905, and 8442 (highest). The corresponding quartile hazard ratios (HRs) associated with mortality adjusted for confounders were 1.00 (reference; lowest quartile), 0.59 (95% confidence interval [CI], 0.47-0.75), 0.54 (95% CI, 0.41-0.72), and 0.42 (95% CI, 0.30-0.60; highest quartile), respectively (P < 0.01). A higher mean step count per day, up to approximately 7500 steps/day, corresponded with progressive and steady decline in mortality HRs using spline analyses. Similar results were observed using sensitivity analyses that minimized reverse causation bias. While the adjusted analysis of measures of stepping intensity showed an inverse association with mortality rates, these associations were no longer significant after accounting for steps per day. Specifically, adjusted HRs comparing highest to lowest quartile were 0.87 (95% CI, 0.68-1.11) for peak 1-minute cadence; 0.86 (95% CI, 0.65-1.13) for peak 30-minute cadence; 0.80 (95% CI, 0.62-1.05) for maximum 5-minute cadence; and 1.27 (95% CI, 0.96-1.68) for time spent at a stepping rate of ≥ 40 steps/minute.
Conclusion. Older women who took approximately 4400 steps per day had lower all-cause mortality rates during a follow-up period of 4.3 years compared to those who took approximately 2700 steps each day. Progressive reduction in mortality rates was associated with increased steps per day before leveling at about 7500 steps/day. Stepping intensity, when accounting for number of steps taken per day, was not associated with reduction in mortality rates in older women.
Commentary
The health and mortality benefits of exercise are well recognized. The 2018 Department of Health and Human Services Physical Activity Guidelines (DHHS-PAG) recommend that adults should do at least 150 to 300 minutes of moderate-intensity aerobic physical activity per week, or 75 to 150 minutes of vigorous-intensity aerobic physical activity per week, in addition to doing muscle-strengthening activities on 2 or more days a week.1 Importantly, the guidelines emphasize that moving more and sitting less benefit nearly everyone, and note that measures of steps as a metric of ambulation can further promote translation of research into public health recommendations for exercise interventions. Despite this recognition, there is limited information centering on the number of daily steps (step volume) and the intensity of stepping that are needed to achieve optimal health outcomes in older adults. The study reported by Lee and colleagues adds new knowledge regarding the relationship between step volume and intensity and mortality in older women.
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
Study Overview
Objective. To evaluate the association of number of steps taken per day and stepping intensity with all-cause mortality in older women.
Design. This was a prospective cohort study of US women participating in the Women’s Health Study (WHS). Participants wore an accelerometer device (ActiGraph GT3X+, ActiGraph Corp, Pensacola, FL) on the hip during waking hours for 7 consecutive days between 2011 and 2015. The accelerator data were collected at 30 Hz and aggregated into 60-second, time-stamped epochs. Data from participants who were adherent with wearing devices (defined as ≥ 10 hours/day of wear on ≥ 4 days) were used in an analysis that was conducted between 2018 and 2019. The exposure variables were defined as steps taken per day and measures of stepping intensity (ie, peak 1-minute cadence; peak 30-minute cadence; maximum 5-minute cadence; and time spent at a stepping rate of ≥ 40 steps/minute, reflecting purposeful steps).
Setting and participants. In total, 18,289 women participated in this study. Of these, 17,708 wore and returned their accelerometer devices, and data were downloaded successfully from 17,466 devices. Compliant wearers of the device (≥ 10 hours/day of wear on ≥4 days) included 16,741 participants (96% compliance rate of all downloaded device data).
Main outcome measure. All-cause mortality as ascertained through the National Death Index or confirmed by medical records and death certificates.
Main results. In this cohort of 16,741 women, average age at baseline was 72.0 ± 5.7 years (range, 62 to 101 years) and the mean step count was 5499 per day (median, 5094 steps/day) during the 7-day data capture period between 2011 and 2015. Not taking steps (0 steps/minute) accounted for 51.4% of the recorded time, incidental steps (1 to 39 steps/minute) accounted for 45.5%, and purposeful steps (≥ 40 steps/minute) accounted for 3.1%. The mean follow-up period was 4.3 years; during this time, 504 participants died. The median steps per day across quartiles were 2718 (lowest), 4363, 5905, and 8442 (highest). The corresponding quartile hazard ratios (HRs) associated with mortality adjusted for confounders were 1.00 (reference; lowest quartile), 0.59 (95% confidence interval [CI], 0.47-0.75), 0.54 (95% CI, 0.41-0.72), and 0.42 (95% CI, 0.30-0.60; highest quartile), respectively (P < 0.01). A higher mean step count per day, up to approximately 7500 steps/day, corresponded with progressive and steady decline in mortality HRs using spline analyses. Similar results were observed using sensitivity analyses that minimized reverse causation bias. While the adjusted analysis of measures of stepping intensity showed an inverse association with mortality rates, these associations were no longer significant after accounting for steps per day. Specifically, adjusted HRs comparing highest to lowest quartile were 0.87 (95% CI, 0.68-1.11) for peak 1-minute cadence; 0.86 (95% CI, 0.65-1.13) for peak 30-minute cadence; 0.80 (95% CI, 0.62-1.05) for maximum 5-minute cadence; and 1.27 (95% CI, 0.96-1.68) for time spent at a stepping rate of ≥ 40 steps/minute.
Conclusion. Older women who took approximately 4400 steps per day had lower all-cause mortality rates during a follow-up period of 4.3 years compared to those who took approximately 2700 steps each day. Progressive reduction in mortality rates was associated with increased steps per day before leveling at about 7500 steps/day. Stepping intensity, when accounting for number of steps taken per day, was not associated with reduction in mortality rates in older women.
Commentary
The health and mortality benefits of exercise are well recognized. The 2018 Department of Health and Human Services Physical Activity Guidelines (DHHS-PAG) recommend that adults should do at least 150 to 300 minutes of moderate-intensity aerobic physical activity per week, or 75 to 150 minutes of vigorous-intensity aerobic physical activity per week, in addition to doing muscle-strengthening activities on 2 or more days a week.1 Importantly, the guidelines emphasize that moving more and sitting less benefit nearly everyone, and note that measures of steps as a metric of ambulation can further promote translation of research into public health recommendations for exercise interventions. Despite this recognition, there is limited information centering on the number of daily steps (step volume) and the intensity of stepping that are needed to achieve optimal health outcomes in older adults. The study reported by Lee and colleagues adds new knowledge regarding the relationship between step volume and intensity and mortality in older women.
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
1. Piercy KL, Troiano RP, Ballard RM, et al. The physical activity guidelines for Americans. JAMA. 2018;320:2020-2028.
2. Jefferis BJ, Parsons TJ, Sartini C, et al. Objectively measured physical activity, sedentary behaviour and all-cause mortality in older men: does volume of activity matter more than pattern of accumulation? Br J Sports Med. 2019;53:1013-1020.
3. Yamamoto N, Miyazaki H, Shimada M, et al. Daily step count and all-cause mortality in a sample of Japanese elderly people: a cohort study. BMC Public Health. 2018;18:540.
4. Dwyer T, Pezic A, Sun C, et al. Objectively measured daily steps and subsequent long term all-cause mortality: the Tasped prospective cohort study. PLoS One. 2015;10:e0141274.
5. Sullivan AN, Lachman ME. Behavior change with fitness technology in sedentary adults: a review of the evidence for increasing physical activity. Front Public Health. 2016;4:289.
1. Piercy KL, Troiano RP, Ballard RM, et al. The physical activity guidelines for Americans. JAMA. 2018;320:2020-2028.
2. Jefferis BJ, Parsons TJ, Sartini C, et al. Objectively measured physical activity, sedentary behaviour and all-cause mortality in older men: does volume of activity matter more than pattern of accumulation? Br J Sports Med. 2019;53:1013-1020.
3. Yamamoto N, Miyazaki H, Shimada M, et al. Daily step count and all-cause mortality in a sample of Japanese elderly people: a cohort study. BMC Public Health. 2018;18:540.
4. Dwyer T, Pezic A, Sun C, et al. Objectively measured daily steps and subsequent long term all-cause mortality: the Tasped prospective cohort study. PLoS One. 2015;10:e0141274.
5. Sullivan AN, Lachman ME. Behavior change with fitness technology in sedentary adults: a review of the evidence for increasing physical activity. Front Public Health. 2016;4:289.