Ekelund U, Tarp J, Fagerland MW, Johannessen JS, et al. Joint associations of accelerometer measured physical activity and sedentary time with all-cause mortality: a harmonised meta-analysis in more than 44,000 middle-aged and older individuals. Br J Sports Med. 2020;54(24):1499-1506.
A meta-analysis of earlier studies on the association between physical activity, sedentary time, and total mortality using data gathered via accelerometer.
Researchers harmonized for analysis individual-level data from 8 studies (N=36,383). The mean age of participants was 62.6 years; 72.8% were women; and the median follow-up was 5.8 years (range 3.0–14.5 years), yielding a total of 243,766 person years. A total of 2,149 (5.9%) deaths occurred in the combined participants.
All-cause mortality: Researchers checked death registries for about a decade after people had joined their respective studies.
Activity measurements: Researchers used accelerometry readings to categorize participants into activity levels.
They put the data through various adjustments for age and sex (model 1), then with additional adjustments for socioeconomic status and body mass index (model 2), and then with the other covariates included in the original studies including smoking, other diseases, and health status (model 3). In a final adjustment, they excluded all deaths that occurred within the first 2 years of follow-up (model 4).
A further breakdown of data examined whether there was a dose-response association between sedentary time and all-cause mortality and whether this differed by physical activity levels for each of the models (1–4).
In this analysis, 30 to 40 minutes daily of moderate- to vigorous-intensity physical activity (MVPA) was associated with a statistically significant reduction in risk of death during the follow-up period.
In each of the 4 adjusted models, participants were ranked into quartiles of exercise intensity. Compared to those in the least-active quartile, any level of physical activity regardless of intensity was associated with a substantially lower risk of mortality. The magnitude of lowered risk was most pronounced for total physical activity; hazard ratios (95% confidence intervals) for increasing quartile were: 1.00 (referent, least active), 0.48 (0.43 to 0.54), 0.34 (0.26 to 0.45), and 0.27 (0.23 to 0.32).
The risk reductions were most pronounced when the second quartile was compared against the lowest activity level for all adjustment models, implying any time spent moving is preferred to being sedentary. For example, the risk was reduced to 0.55 (0.49 to 0.63) in the second quartile for high light-intensity physical activity and additionally reduced in the third (0.38, 0.30 to 0.48) and fourth (0.37, 0.32 to 0.46) quartiles compared with the referent lowest level. Higher levels of MVPA were also associated with a reduced risk of death even after adjustment for sedentary time.
The risk of death increased with increasing time spent sitting; hazard ratios for increasing quartiles were: 1.00 (referent), 1.28 (1.09 to 1.51), 1.71 (1.36 to 2.15), and 2.63 (1.94 to 3.56) in models that adjusted for age, sex, body mass index (BMI), socioeconomic status, and time spent in MVPA.
Past research has associated physical activity with many chronic diseases and higher risk of morbidity and mortality.1 These results bring greater clarity to the subject. Some past meta-analyses of these data have suggested that the effect of sedentary behavior on morbidity and mortality are independent of physical activity; in other words, it doesn’t matter how much you exercise because the amount you sit is what predicts ill health and mortality and exercise doesn’t change this.2 Other large-scale meta-analyses and cohort studies suggest that high levels of physical activity reduce this association with sitting, suggesting that high-intensity exercise might neutralize the harm caused by sedentary lifestyles.3
The amount of exercise required to counter the effects of sitting has varied widely between studies. For example, in Ekelund’s 2016 meta-analysis that examined more than a million adults, eliminating the increased risk of death associated with sitting time required 60 to 75 minutes of daily physical activity.3 On the other hand, in 2019 Stamatakis et al concluded that just 150 to 300 min of exercise per week was enough to neutralize any association between sitting and death.4
Using [accelerometers] to measure activity duration and intensity, as well as time spent sitting, rather than self-assessments proves to be a game changer; it creates a level of accuracy previously unobtainable.
Up to this point, all of these meta-analyses have relied on self-reported assessments of exercise time and intensity as well as the amount of time spent sitting. Such self-assessments have not proven accurate for categorization of exercise or sedentary behaviors because of what is called a social desirability bias. Put simply, people tend to describe their own behaviors in ways that make them sound better. Self-assessment tends to underestimate sedentary time and overestimate exercise intensity and total activity.5 Combining inaccurate data from multiple individual studies into a meta-analysis compounds the inaccuracies.
This current 2020 meta-analysis by Ekelund et al improves the quality of results by using only data from studies that categorized participant activity by accelerometer measurement. Using these devices to measure activity duration and intensity, as well as time spent sitting, rather than self-assessments proves to be a game changer; it creates a level of accuracy previously unobtainable.
Thus, the results from this study are more likely to be accurate than what was previously reported. We can now provide patients with information that may encourage them to change activity levels. For example, we can say, as The New York Times did in reporting this study, that “people in the top third for sitting and bottom third for activity have about 260 percent more likelihood of premature death than the men and women who moved the most and sat the least.”7
Or, as the article stated, that “People in the middle third for activity, who exercised moderately for about 11 minutes a day, were significantly less likely to have died prematurely than people who moved less, even if all of them belonged to the group that also sat the most.”7 The “sweet spot for physical activity and longevity seemed to arrive at about 35 minutes a day of brisk walking or other moderate activities, an amount that led to the greatest statistical improvement in life span, no matter how many hours someone sat.”6
While we are on the subject of exercise and mortality, another recent study should be mentioned. In October 2020, the results of a 5-year prospective, randomized, controlled trial on exercise training and mortality was published. Stensvold et al conducted this ambitious study in Trondheim, Norway, starting in 2012.7 The researchers invited all the city’s inhabitants aged between 70 and 77 years to participate in their study. About 5,000 declined the invitation, but 1,567 did participate. These participants were randomized into 3 groups that were assigned to 3 different exercise protocols. The control group (n=780) followed the Norwegian National Guidelines for Physical Activity that prescribe 30 minutes of moderate-level physical activity almost every day. The other participants were split into 2 groups. They, too, followed the national guidelines but were asked to substitute 2 of their 5 weekly exercise sessions with 1 of 2 experimental regimes. One group (n= 387) added 2 sessions of moderate-intensity continuous training (MICT) while the other experimental group (n=400) performed high-intensity interval training (HIIT).
The HIIT sessions consisted of a 10-minute warm-up followed by 4 intervals, each 4 minutes long, at about 90% of peak heart rate, while the MICT sessions consisted of 50 minutes of continuous work at about 70% of peak heart rate. As in other studies, the researchers were interested in all-cause mortality.
The mortality rate for all groups together was 4.6% (n=72). The control group following national guidelines had a slightly higher-than-average mortality at 4.7% (n=37). The combined MICT and HIIT groups had a slightly lower mortality at 4.5% (n=35). However, the MICT group alone had the seemingly highest mortality at 5.9% (n=23) and the HIIT group the lowest at 3.0% (n=12). However, these differences in mortality between groups did not reach statistical significance.
When researchers examined MICT and HIIT separately and compared them with the control group, HIIT was associated with a 1.7% risk reduction (hazard ratio 0.63, 95% confidence interval 0.33 to 1.20) while MICT group had a 1.2% increase in risk. Again, these were trends and were not statistically significant differences.
“No differences were observed in cardiovascular disease, cancer, or related events between the control group and the combined MICT and HIIT group, or any effect of exercise intensity,” the authors wrote.8
A number of factors may account for not seeing significant differences between these groups. The nature of these experimental interventions was hard to hide from participants, and some in the control group opted to mimic the exercise lifestyle that they expected to be most beneficial. Some individuals in the control group who were supposed to follow only the national guidelines added HIIT workouts to their regimes, and in the end about 20% of them were doing HIIT. Thus, the control group was working out harder than the MICT group.
According to a 2019 report, only 33% of the older adults in Norway meet the government’s suggested level of exercise, the level to which the researchers told the MICT group to aspire.8 All the groups in the study did better than this: “At baseline, 273 (35%) of participants in the control group, 155 (40%) in the MICT group, and 148 (37%) in the HIIT group followed national guidelines for physical activity,” the authors reported.
Nothing prevented participants from exercising more than what they were instructed to do. Over time, participants in the control and the MICT groups began adding interval training to their workouts, so that about 20% of the control group and 13% of the MICT group had shifted their workout routines to mimic the HIIT group’s routine. This, combined with the fact that only about half of the HIIT group met their exercise regime requirement, meant that the distinctions between how much exercise the various groups were performing lacked clarity.
Older adults who were willing to participate in this study may simply exercise too much to see a significant difference in outcomes. At baseline, 80% of the participants were already exercising regularly. There also might not be so great a difference between these various “schools” of workout regimes. Proponents of various styles of exercise all insist that their routines yield superior benefit, but perhaps it doesn’t matter as much as they claim. Exercise is beneficial; how much, how intense, and other such details may not matter. One should note that over the 5 years of this study, the predicted death rate for adults in Norway in the same age bracket as this study’s participants was 10%. That is more than twice of what was seen for the individuals who participated in this study.9
In the end, the Norwegian study does not provide strong evidence of the superiority of 1 exercise regime over another, but it certainly does enforce Ekelund’s results. Exercising regularly is associated with a lower risk of mortality over the short term. Any form of regular exercise is associated with a lower relative risk of dying.