By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
Dr. Feldman reports no financial relationships relevant to this field of study.
SYNOPSIS: A large meta-analysis including data from more than one million subjects and 16 studies revealed that specified levels of moderate-intensity physical activity can significantly lessen the health risks of sedentary lifestyles.
SOURCE: Ekelund U, Steene- Johannessen J, Brown WJ, et al; Lancet Physical Activity Series 2 Executive Committee; Lancet Sedentary Behaviour Working Group. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet 2016; Jul 27. doi: 10.1016/S0140-6736(16)30370-1. [Epub ahead of print].
- The goal of this meta-analysis was to evaluate the evidence that physical activity can attenuate the health risks of prolonged sitting and/or TV viewing time.
- Results of analysis of data regarding prolonged sitting time found that 60-75 minutes of moderate-intensity physical activity eliminated the increased risk of all-cause mortality seen with prolonged sitting; lesser amounts of activity time appeared to attenuate the risk.
- Results of the TV viewing time data suggested that TV viewing time for more than three hours daily was associated with an increased risk of all-cause mortality except at the highest level of exercise.
- For all groups, the risk of all-cause mortality associated with higher time spent in sedentary activities was attenuated with physical activity, although to varying degrees.
The 2012 Olympics in London provided a backdrop for the first Lancet series on the health implications of physical activity.1 The articles in this series definitively established physical inactivity as a global pandemic with public health implications.2 This year, Lancet published a second physical activity series with four papers, each one contributing to the field in a slightly different manner.3 Updated information on national health strategies, scaling interventions to affect large and diverse populations, and the economic burden of physical inactivity are topics covered in three of the papers. The fourth paper, discussed here, took an analytical look at mitigating the health risk of inactivity by analyzing data regarding sitting time independent from physical activity. A major goal was to determine if physical activity can reduce the health risk of long periods of inactivity.
The title of this discussion is borrowed from the topic of a 1953 Lancet paper,4 which looked at the increased risk of coronary heart disease among London bus drivers when compared with conductors. Since that time, several meta-analyses have studied prolonged TV viewing time and sitting time.5,6 Clear evidence exists of an elevated risk of type 2 diabetes, cardiovascular disease, stroke, specific cancers, and premature death associated with both of these sedentary habits. Ekelund et al set out to determine if these risks remained independent of physical activity or if specified amounts of physical activity could affect and/or reverse the risks.
This meta-analysis involved 16 studies, 13 of which included data regarding sitting and all-cause mortality and morbidity. More than 1 million people followed from 2-18 years were involved in these studies (including 84,609 deaths.) Three of the 13 studies and three additional studies contained data on TV viewing time and were analyzed separately. These involved 465,450 individuals and 43,740 deaths.
The team faced a task of reconciling data from different sources. To compare levels of physical inactivity and TV viewing, data from each study were reanalyzed and placed into one of several time-dependent groups. Physical activity categories were calculated by contacting the authors of the contributing studies and asking for a translation from the original reports of intensity of physical activity into a standardized format to allow comparisons between studies.
Results were reported according to several different perspectives. Across all categories of sitting time, the risk of all-cause mortality appeared reduced at higher levels of physical activity and eliminated at the highest level (65-75 minutes of moderate intensity exercise/day). For TV viewing time, the results showed a similar pattern, except that at the highest level of TV viewing (> 5 hours/day) even the highest level of physical activity could not eradicate the risk of all-cause mortality, although there is clear attenuation of risk.
Figures 1 and 2 show the effect of varying levels of sitting (see Figure 1) or TV viewing (see Figure 2) within each quartile of physical activity. The referent was assigned a value of 1 and all-cause mortality was measured. For each case (sitting time or TV viewing time), the referent was the least amount of time — < 4 hours/day sitting time or < 1 hour/day TV viewing time.
Figure 1 shows these results with grouping representing progressive levels of physical activity. Each group was standardized within itself. These results were not meant to compare between levels of activity but within each activity level to determine if activity level could affect all-cause mortality at different levels of sitting. Note that the risk of mortality associated with sitting longer disappears in the most active group. The other three quartiles of physical activity showed increased mortality with increased sitting time compared to the referent level of sitting < 4 hours/day. Note the moderation of effect for those sitting > 8 hours/day, even in quartile 2 and 3 of physical activity.
Figure 2 looks at TV viewing time with a referent value of 1 assigned to those watching < 1 hour of TV/day. Figure 2 shows the association between TV viewing time and all-cause mortality in each quartile of physical activity. Note the progressive increase in duration of physical activity has a clear effect only for the highest level of physical activity (60-75 minutes.)
Lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save it and preserve it. ~Plato
The second Lancet series on physical activity brings us new information in a methodical form, but also reminds us of what we have known for centuries — the importance of movement and exercise in maintaining and attaining physical health. The analytic nature and results from Ekeland’s group can help practitioners communicate to patients definitive information about duration and intensity of exercise and about the benefits of activity.
It is interesting that the results of TV viewing differ from the results seen when looking just at sitting time and that the effect of progressively higher levels of exercise does not seem as significant when looking at higher amounts of viewing time. Notably, there were fewer studies and fewer number of participants in the TV viewing studies, which may have affected results. The authors speculated that the frequent association of TV viewing with eating also may play a role; this is certainly an area “ripe” for further exploration given the potential for remediation.
It also would be useful in further studies to study whether computer time or any “screen time” differs from TV viewing time in risk of all-cause mortality. For example, do individuals who play video or computer games for > 5 hours/day carry the same risk of all-cause mortality as do TV viewers at comparable lengths of time? A hard look at this may help better delineate the specific risks of TV viewing.
All studies included in the meta-analysis attempted to control for chronic or debilitating illnesses. However, the possibility that an underlying illness confounded the results by affecting time in sedentary activities (and independently led to a higher risk of all-cause mortality) cannot be excluded based on the information presented.
Although the authors freely noted the studies were weakened by the self-reported nature of both the inactivity and physical activity sets of data (as well as the possibility of unrecognized factors affecting ability to engage in activity), there was certainly an impressive strength in number of participants and data generated that cannot be overlooked or dismissed. Informing patients that there are health risks to inactivity, but that these risks can be mitigated by activity, will be welcome news to many.
Of course, the most powerful level of mitigation may feel like an intimidating amount of physical activity. Data from this large meta-analysis show that 60-75 minutes of moderate intensity activity/day is the level at which the health risk of sitting eight hours a day or more disappears. Notably, this is above the level of most physical activity recommendations for public health and at the high end (“for even greater health benefits”) of U.S. recommendations:
U.S. Department of Health Physical Activity Guidelines7
For substantial health benefits, do one of the following:
- 150 minutes each week of moderate-intensity aerobic physical activity (such as brisk walking or tennis)
- 75 minutes each week of vigorous-intensity aerobic physical activity (such as jogging or swimming laps)
- An equivalent combination of moderate- and vigorous-intensity aerobic physical activity
Do aerobic physical activity in episodes of at least 10 minutes and, if possible, spread it out through the week. For even greater health benefits, do one of the following:
- Increase moderate-intensity aerobic physical activity to 300 minutes each week
- Increase vigorous-intensity aerobic physical activity for 150 minutes each week
When this study is viewed as part of the overall Lancet series, the global, economic, and public health implications of physical inactivity become clear and alarming. There is a clear place here not only for the individual practitioner, but also for policy and public health experts.
Long periods of inactivity often are part of a modern-day workplace and lifestyle. The integrative practitioner holds a unique role that is well suited to let patients know about the harmful effects and risks associated with inactivity and that “stepping up activity” can help mitigate these risks. Although many questions remain about etiology and specific mechanisms, sound evidence backs a clear recommendation to reduce sitting time and TV viewing time (< 3 hours per day) and to increase time spent on moderate-intensity activity. Specific recommendations can help the “bus drivers” of our society avoid the health risks inherent in sedentary lifestyles.
- Lancet series. Physical Activity, Lancet July 18, 2012. Available at: http://www.thelancet.com/series/physical-activity. Accessed Sept. 7, 2016.
- Lee IM, Shiroma EJ, Lobelo F, et al. Effect of physical inactivity on major non-communicable diseases worldwide: An analysis of burden of disease and life expectancy. Lancet 2012;380:219-229.
- Lancet Series: Physical Activity 2016: Progress and Challenges, Lancet July 27, 2016. Available at: http://www.thelancet.com/series/physical-activity-2016. Accessed Sept. 7, 2016.
- Morris JN. London Transport Workers Study. Coronary heart disease and physical activity of work. Lancet 1953;265:1053-1057.
- Wilmot EG, Edwardson CL, Achana FA, et al. Sedentary time in adults and the association with diabetes, cardiovascular disease and death: Systematic review and meta-analysis. Diabetologia 2012;55:
- Proper K, Singh AS, van Mechelen W, Chinapaw MJ. Sedentary behaviors and health outcomes among adults: A systematic review of prospective studies. Am J Prev Med 2011;40:174-182.
- Office of Disease Prevention and Health Promotion. Physical Activity Guidelines for Americans. Available at: https://health.gov/paguidelines/guidelines/. Accessed Sept. 7, 2016.