Replace sitting time with physical activity and take care of your heart
We spend a large proportion of our waking hours sitting, but sitting for long hours increases the risk of cardiovascular disease and other conditions, research shows. However, it is less clear how much physical activity is needed to offset the risk of sitting. An Australian prospective population study is attempting to address this.
The results of the study, just published in the Journal of the American College of Cardiology, show that about 20-40 minutes of physical activity per day may be enough to eliminate many of the health risks associated with sitting. The study also shows that the risk of dying from cardiovascular disease is further reduced by higher levels of physical activity.
Sitting for more than 8 hours a day is dangerous
The study is based on almost 150,000 adults aged 45 and over, who were followed for an average of 8.9 years. Participants self-reported how many hours a day they spent sitting, standing, sleeping and being physically active. Combined with mortality data, the researchers were able to look at the association between sitting still, the level of physical activity and overall mortality and death from cardiovascular disease.
The researchers found that people who were physically inactive and sat for more than eight hours a day were more than twice as likely to die from cardiovascular disease compared to a reference group of people who were physically active for at least one hour a day and sat for less than four hours a day.
However, the number of hours spent sitting was not the decisive factor if you were also physically inactive. People who were physically active for less than 20 minutes a day and who sat for less than four hours a day had a 44-60% higher risk of dying from cardiovascular disease compared to the more physically active reference group.
A large data base
One of the strengths of the study, according to Mads Lind, Senior Consultant at the Danish Heart Foundation's Prevention Department, is that it is based on data from so many people.
- The study is notable for its very large size and for the methodology used to examine the relationship between the amount of sedentary time and different levels of physical activity in the same people, he explains.
However, these conclusions should be seen in the light of the fact that participants only reported their behavior at the beginning of the study.
- A weakness of the study is that the physical activity of the participants during the follow-up period is not known. It is assumed that the level they reported at baseline is an indicator for the entire relatively long observation period, but we can't really know if it fits, Mads Lind explains.
Active time versus sitting time
The researchers also looked at what it meant to replace sitting still with either an hour of standing, walking or moderate to vigorous physical activity. They found that even a small amount of effort had a big effect.
Among those who sat for more than six hours a day, replacing one hour of sitting with moderate physical activity such as gardening or cleaning meant a 20% reduction in the risk of dying from cardiovascular disease. Replacing one hour of sitting with more vigorous physical exercise, such as swimming or playing tennis, was even more beneficial - a 64% reduction in the risk of dying from cardiovascular disease.
However, according to senior consultant Mads Lind, the conclusions on the impact of replacing sedentary time with active time should be taken with some caution.
- In the study, the researchers used an indirect method to estimate the impact of replacing sedentary time with active time and did not examine it directly. They did not look at specific individuals and measure what it meant that they changed their physical activity level. Instead, the researchers have methodically been able to modulate it in the theoretical model, which of course makes the results a little less credible, Mads Lind explains, but continues:
- However, this does not change the fact that the study points to the importance of moderate to vigorous physical activity, even if you have a sedentary job, for example, and that it can make a significant difference to your risk of dying from cardiovascular disease.
A little can go a long way
For Dorthe Kjærgaard-Jensen, a physiotherapist and advisor at the Danish Heart Foundation, the study's conclusions are also interesting.
- We sit down a lot in today's Denmark, and in many cases this can be difficult to change. But the study helps to support the idea that by moving just a little bit, we can partly compensate for all the time we spend sitting down. This means that common advice such as cycling to work, getting off a station earlier than usual and walking the last bit or taking the stairs instead of the elevator actually plays a significant role. A lot can be achieved by doing just a little," she explains.
Dorthe Kjærgaard-Jensen also notes that the study shows that for the very physically inactive, there is so much benefit to be gained by moving just a little.
- It's interesting that for those who are hardly physically active, just getting up from the chair and moving a little can really make a difference. This is perhaps something we haven't focused on as much, and from a prevention perspective, it's important to remind ourselves that increased efforts for the most inactive people actually make the biggest difference," explains Dorthe Kjærgaard-Jensen.
Thanks to the Danish Heart Foundation; https://hjerteforeningen.dk/fagnet/2019/09/26/erstat-siddetid-med-fysisk-aktivitet-og-pas-paa-hjertet/
Read the article published in the Journal of the American College of Cardiology and listen via the same link to a podcast with the editor-in-chief of JACC Dr. Valentin Fuster's summary and comments on the article http://traffic.libsyn.com/jaccaudio/JACC7316_fustersummary_05.mp3):
Stamatakis E, Gale J, Bauman A, Ekelund U, Hamer M, Ding D. Sitting Time, Physical Activity, and Risk of Mortality in Adults. Journal of the American College of Cardiology. Volume 73, Issue 16, April 30, 2019, Pages 2062-2072
