Regular Exercise Can Offset the Mortality Risk of Long-term Sitting, Meta-analysis Finds

People who sit for prolonged periods are at higher risk of mortality, but that risk can be offset if they get at least 60 minutes of moderate physical activity per day, according to a new meta-analysis.

The study, published in The Lancet last week, suggests that current US and World Health Organization recommendations, which call for at least 150 minutes a week, may not go far enough.

“When we talk from a cardioprotective point of view, we talk about 30 minutes of moderate intensity exercise four times a week,” Allan Stewart, MD (Mount Sinai Hospital, New York, NY), who wasn’t involved in the study, told TCTMD. “And what this study is showing is that if you sit over 8 hours a day, that’s not enough.”

The Risk in Sitting

Investigators led by Ulf Ekelund, PhD (Norwegian School of Sport Sciences, Oslo, Norway; University of Cambridge, England), analyzed data on 1,005,791 individuals from 16 studies, two of which were previously unpublished, for levels of physical activity, sitting time, and mortality rates. Follow-up lasted anywhere from 2 years to more than 18 years, during which 84,609 individuals (8.4%) died.

To standardize how exercise was described among the different studies, the investigators requested that the original authors harmonize their data based on a specific protocol with categories of daily sitting time, TV viewing time, and different levels of physical activity based on metabolic equivalent of task (MET) hours per week.

Using the harmonized data, mortality was 59% higher in the least active group (< 2.5 MET hrs/wk) when they sat for at least 8 hours per day than in the most active group (> 35.5 MET hrs/wk) in the groups who sat for less than 4 hours a day. Those who sat for at least 8 hours per day but also had the highest levels of physical activity saw no increase in mortality risk. Among individuals who sat less than 4 hours per day, those who were the least active had a 27% higher risk of dying than those who were the most active.

The lack of association between sitting time and mortality risk in people who got the most exercise—which amounted to 60-75 minutes per day—suggests that physical activity has the ability to offset the harms of prolonged sitting, Ekelund et al say.

Additionally, all-cause mortality risk was much higher in those who watched TV for more than 5 hours a day. In the least active group (< 2.5 MET hrs/wk), the risk increased by 93% but in the most active group (> 35.5 MET hrs/wk), the risk increased by only 16%.

A Patient’s Health on TV

The findings reveal that enough exercise can offset the negative health effects of too much sitting, but they also highlight the fact that watching TV is particularly harmful, according to Ekelund.

“I wasn’t too surprised that high levels of physical activity would eliminate the association between sitting time and mortality,” he said. What was a little surprising, Ekelund added, is the “slight difference between sitting time and TV time.”

The difference could be the result of confounders such as smoking or unhealthy eating, both of which are much easier to do at home in front of the TV than at work where the majority of sitting time likely took place, according to Stewart.

Ultimately, he added, these behaviors stem from how society operates, especially in the United States. “Instead of making our routine [one] of sitting at a desk, coming home, having a dinner, and then sitting in front of a television,” he said, it would be better after dinner to take a walk, go to the gym, or ride a bike.

Physicians, armed with the data of this study and others, need to continue to address these concerns when speaking with patients, according to Stewart. Beyond the usual questions about smoking and alcohol use, a key thing to ask patients is how long they sit during the day, he suggested. “Because it’s not an obvious question to ask.”

Even though exercise’s positive impact makes sense, Ekelund noted, that does not necessarily make it easier for individuals to correct their unhealthy behaviors.

“The general message is that if you have to sit for long hours, try to be as physically active as you can because that would definitely be beneficial for your health,” he said. “I usually say, ‘Sit less, move more, and the more the better.’ It’s simple to say, [but] less simple to implement on a population level, I suppose.”

Michael H. Wilson is the 2016 recipient of the Jason Kahn Fellowship in Medical Journalism.

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