At least an hour of physical activity needed to offset risk for several chronic conditions and mortality
Sedentary behavior has been associated with increased risk of several chronic conditions and mortality. However, it is unclear whether physical activity attenuates or even eliminates the detrimental effects of prolonged sitting. A new study examined the associations of sedentary behavior and physical activity with all-cause mortality.
The meta-analysis of trials involving more than 1 million individuals was reported online July 27 in The Lancet. It is one of a special series of papers on physical activity.
The Lancet notes that its first series on physical activity in 2012 concluded that, “physical inactivity is as important a modifiable risk factor for chronic diseases as obesity and tobacco.” The meta-analysis found that 1 hour of moderate-intensity activity, such as brisk walking or riding a bicycle, can offset the health risks of sitting for 8 hours a day. Twenty-five percent of all individuals in the study reported this level of physical activity. The study also discovered that even shorter periods of 25 minutes a day can be beneficial.
For those of us who work by sitting at a desk, it can be very difficult not to sit while we do our jobs. But, there are still many ways to get moving, like going for a walk during lunch, or even getting up and walking over to an associate to hand them a note instead of sending an email. There are many ways to get in your physical activity.
According to the researchers, the data from more than a million people is the first meta-analysis to use a harmonized approach to directly compare mortality between people with different levels of sitting time and physical activity. They included 16 studies, with data on 1,005,791 individuals (aged >45 years) from the United States, Western Europe, and Australia.
Researchers divided the study participants into four groups based on their reported levels of physical activity: <5 min/day; 25-35 min/day; 50-60 min/day; and 60-75 min/day.
Researchers noted that, “Among the most active, there was no significant relation between the amount of sitting and mortality rates, suggesting that high physical activity eliminated the increased risk of prolonged sitting on mortality.” But as the amount of physical activity decreased, the risk for premature death increased.
Researchers found prolonged sitting associated with an increase in all-cause mortality, mainly due to cardiovascular disease and cancer (breast, colon, and colorectal), noting that, “A clear dose-response association was observed, with an almost curvilinear augmented risk for all-cause mortality with increased sitting time in combination with lower levels of activity.”
Compared with the referent group (i.e., those sitting <4 h/day and in the most active quartile [>35·5 MET-h per week]), mortality rates during follow-up were 12–59% higher in the two lowest quartiles of physical activity (from HR=1·12, 95% CI 1·08–1·16, for the second lowest quartile of physical activity [<16 MET-h per week] and sitting <4 h/day; to HR=1·59, 1·52–1·66, for the lowest quartile of physical activity [<2·5 MET-h per week] and sitting >8 h/day). Daily sitting time was not associated with increased all-cause mortality in those in the most active quartile of physical activity. Compared with the referent (<4 h of sitting per day and highest quartile of physical activity [>35·5 MET-h per week]), there was no increased risk of mortality during follow-up in those who sat for more than 8 h/day but who also reported >35·5 MET-h per week of activity (HR=1·04; 95% CI 0·99–1·10). By contrast, those who sat the least (<4 h/day) and were in the lowest activity quartile (<2·5 MET-h per week) had a significantly increased risk of dying during follow-up (HR=1·27, 95% CI 1·22–1·31). Six studies had data on TV-viewing time (N=465 450; 43 740 deaths). Watching TV for 3 h or more per day was associated with increased mortality regardless of physical activity, except in the most active quartile, where mortality was significantly increased only in people who watched TV for 5 h/day or more (HR=1·16, 1·05–1·28).
In conclusion, the researchers emphasized that high levels of moderate intensity physical activity (i.e., about 60–75 min per day) seem to eliminate the increased risk of death associated with high sitting time. However, this high activity level attenuates, but does not eliminate the increased risk associated with high TV-viewing time. These results provide further evidence on the benefits of physical activity, particularly in societies where increasing numbers of people have to sit for long hours for work and may also inform future public health recommendations.
In another study published online by JAMA Ophthalmology in August, they found that sedentary behavior may be associated with diabetic retinopathy. The analysis included 282 participants with diabetes. The average age was 62 years, 29 percent had mild or worse DR, and participants engaged in an average of 522 min/d of SB. The author found that for a 60-min/d increase in SB, participants had 16 percent increased odds of having mild or worse DR; total PA was not associated with DR. “The plausibility of this positive association between SB and DR may in part be a result of the increased cardiovascular disease risks associated with SB, which in turn may increase the risk of DR. In order to prove a cause and effect of SB and worsening DR s larger study would be needed.”
- Inactivity is linked to a decreased production of certain hormones.
- We need to break up periods of sitting for prolonged periods with short bursts of activity.
- Walking 5 minutes every hour can offset sitting for the other 55 minutes per hour.
AMA Ophthalmology, doi:10.1001/jamaophthalmol.2016.2400, published online 4 August 2016.