Too Much Sitting Linked to Bad Outcomes Around the Globe: PURE

Prolonged sitting time, particularly in low- and middle-income countries but also in wealthier nations, is associated with an increased risk of death and cardiovascular events, a new analysis shows.

Overall, people who sat for 8 hours or more per day had nearly a 20% higher risk of all-cause mortality or CVD events over a median follow-up of 11.1 years when compared with those who sat for less than 4 hours daily. The new results, say researchers, provide support for other studies highlighting the detrimental effects of prolonged sitting and bolster current guidelines that recommend we all sit a little less and move a little more.  

“This is an important risk factor to talk to patients about, just as it would be with smoking,” Scott Lear, PhD (Simon Fraser University and St. Paul’s Hospital, Vancouver, Canada), one of the study’s lead investigators, told TCTMD. “It’s a low-cost intervention. You just have to talk to patients about it but it can have a benefit.”

Prolonged sitting—4 to 8 hours (or more) at a time on a daily basis—has been shown to be associated with higher risks of all-cause mortality, CVD, diabetes, and obesity, as well as other conditions, but the health effects of sedentary behavior have largely been seen in high-income countries (HICs), said Lear. In these countries, prolonged sitting is often because of desk work, with many people getting active once they’re off the clock.

“The activity pattern in these countries is predominantly one where a lot of us will sit most of the day and then do some recreational activity,” said Lear. “That might be a walk, some gardening, a run, or tennis.”

Patterns vary around the world. Recreational activity is largely for the privileged in lower-income countries (LICs) and generally not as common as it is in HICs. The prevalence of a sedentary lifestyle has also increased in lower- and middle-income nations, which have some of the highest rates of CVD. For that reason, researchers wanted to assess the risks of prolonged sitting across a diverse population.

Carl “Chip” Lavie, MD (Ochsner Heart and Vascular Institute, New Orleans, LA), whose group published a large review in 2019 on the ill effects of sedentary behavior, said the new research supports recommendations from the US Department of Health and Human Services and the World Health Organization to sit less and move more.   

“In a perfect world, everyone would be physically active and sit less than 4 hours per day,” Lavie told TCTMD. “These data suggest that the impact of prolonged sitting is even greater in low-income as opposed to high-income countries such as ours, but it is still applicable in the US. It is bad to be sitting over 6 hours per day and even worse for more than 8 hours per day. Other studies show even more [risks] over 9.5 hours per day. It makes sense that the more sitting, the worse outcomes.”

The study was published online June 15, 2022, in JAMA Cardiology.

The PURE Study

The analysis was based on data from 21 countries, with 105,677 participants (mean age 50.4 years; 41.4% male) who completed at least one cycle of follow-up visits in the Prospective Urban Rural Epidemiology (PURE) study. Included are four HICs, seven upper-middle-income countries (UMICs), five lower-middle-income countries (LMICs), and five LICs.  

The median sitting time was 4.0 hours, with a range from 2.6 hours in Poland and Chile to 7.3 hours in Saudi Arabia. People with higher sitting times were more likely to be from urban areas, from HICs and UMICs, and to have more education. Those who sat the most also had higher INTERHEART risk scores, were less physically active, and were more likely to have diabetes, depression, physical impairments, and chronic disease at baseline. 

In the multivariable-adjusted model, the risk of all-cause mortality and cardiovascular events was significantly elevated at sitting times of 6 hours per day or more. For those who sat 6 to 8 hours per day and more than 8 hours per day, the risks of all-cause mortality and CVD events were 13% and 19% higher, respectively, compared with those who sat less than 4 hours per day (P for trend < 0.001).

Compared with the reference group (< 4 hours per day), sitting for 8 hours or more was associated with higher risks of the following outcomes:

• All-cause mortality (HR 1.20; 95% CI 1.10-1.31)
• CVD mortality (HR 1.29; 95% CI 1.10-1.51)
• Major CVD events (HR 1.21; 95% CI 1.10-1.34)
• MI (HR 1.20; 95% CI 1.04-1.38)
• Stroke (HR 1.20; 95% CI 1.03-1.40)
• Heart failure (HR 1.49; 95% CI 1.16-1.90)

Stratified by country-income levels, there was a significant interaction between income and daily sitting time for the composite endpoint of all-cause mortality and CVD events and for all-cause mortality alone. The association between sitting time and the composite endpoint was stronger in LICs and LMICs than in HICs and UMICs (P = 0.02 for interaction).

Sitting’s Impact Varies by Economic Region

Researchers can only speculate why those in LICs and LMICs were more greatly impacted by prolonged sitting. In HICs, most people are sitting down for such long stretches because of work, most likely at higher-paying jobs.

“We know that people with higher incomes tend to have better health outcomes,” said Lear. “It might be because of education, or it might be because of greater access to [healthcare] services than those people lower down on the economic ladder. Definitely, higher-income earners in India are likely sitting more, but that’s a smaller percentage than what we would see in Canada and Sweden, which are two of the higher-income countries.”

What people are doing when they are sitting might may also impact the risks, suggest researchers. Poor nutrition often accompanies watching television, for example. Also, Lear speculated that cognitive stimulation might even play a role.

One of the big questions that comes up in this line of research is whether exercise can offset the risks associated with prolonged sitting. In PURE, researchers found that among those sitting for 8 hours or more per day, the risk of death/CVD events increased 17% to 50% across different physical-activity levels. However, those who sat this long, but who reported moderate-to-high daily physical activity levels, had a similar risk of death/CVD as those who sat the least (< 4 hours per day) and who also had low physical activity levels.

These results suggest that exercise can counteract the effects of prolonged sitting, even if it’s not the most ideal exercise pattern, said Lear.

The researchers also found that replacing 30 minutes of sitting with exercise or physical activity reduced the risk of mortality/CVD by about 2%. “There’s definite value in making that exchange and doing some activity during the day,” said Lear. He noted that sitting for 8 or more hours per day, when it was combined with little physical activity, accounted for 8.9% of deaths in the study. Smoking, on the other hand, accounted for 10.6% of all deaths.

“Sitting for prolonged periods of time, with little exercise, is almost as problematic as smoking,” said Lear.

To TCTMD, Lavie had similar advice about getting up and doing something—anything but staying still—during the day.

“Although even physically active people would ideally avoid prolonged sitting, high physical activity, especially very high, mostly negates the adverse effects of prolonged sitting,” he said. “Ideally some of the sitting time should be replaced with walking or even getting up every 30 to 60 minutes or so and doing a short walk or even walking at one’s desk to produce some leg muscle movement.”  

In terms of his recommendations, Lear said that physicians also need to sit less and move more. “It’s not just talking to patients about it, but living it as well,” he said. “We do know that doctors who are more active tend to counsel patients on exercise more and patients tend to listen to that message more.”