A new study has found that regularly sitting for prolonged periods of time is a risk factor for premature death. The findings were published in the Annals of Internal Medicine on Oct. 3, 2017.
The study followed nearly 8,000 adults aged 45 and older over a four year period. Researchers found that people who sat the most had nearly twice the risk of dying over those four years than people who sat the least. The risk of an early death increases not only with total number of hours spent seated per day, but also with long periods of uninterrupted sitting. Taking a break to walk around every 30 minutes seemed to help decrease the risk of an early death.
Negative effects caused by excessive sitting were not affected by the participants’ age, sex, race or BMI. The findings also indicate that exercising daily or semi-daily does not negate the effects of sedentary behavior.
“What’s most troubling is it’s like I exercise in the morning and I think I’m good,” said lead researcher Keith Diaz, “but in addition to exercise I should also be mindful of not being sedentary for long periods throughout the day.” Diaz is an associate research scientist at Columbia University Medical Center in New York City.
Diaz mentioned that there should be guidelines for sitting, much like the CDC’s guidelines for exercising. “We think a more specific guideline [for sitting] could read something like, ‘For every 30 consecutive minutes of sitting, stand up and move/walk for five minutes at brisk pace to reduce the health risks from sitting.'”
Study Methods and Findings
Previous studies have found links between prolonged sitting and early death. But those studies usually relied on participants’ personal testimony of their sitting habits, an iffy method to say the least. However this new study tracked participants’ sitting time with a hip-mounted accelerometer, then correlated movement time with the risk of death during the study period.
Researchers found that, on average, sedentary behavior accounted for just over 12 hours of a person’s 16-hour waking day. The average time spent sitting at a stretch, i.e. one sitting, was 11 minutes. Over an average follow-up of four years, 340 participants died.
It is interesting to note the differences between total daily sedentary time and uninterrupted sedentary time. For instance, people with uninterrupted sitting times of 30 minutes or longer had the highest risk of death if daily sitting time was longer than 12.5 hours per day. However, for those whose total daily sedentary times were low, single-sitting stretch time had no effect on mortality.
“We found that there wasn’t a threshold or cutoff where one’s risk for death dramatically increased,” said Diaz. “To give you a specific number, those who sat for more than 13 hours per day had a 2-fold (or 200 percent) greater risk of death compared to those who sat for less than about 11 hours per day.”
Stretch-time sitting and its impact on death proved to be a bit harder to pinpoint. Nevertheless, the study indicated that participants who regularly sat for less than 30 minutes at a time had a 55 percent lower chance of death than those who usually sat for longer than 30 minutes at a stretch. And those who frequently sat for more than 90 minutes at a stretch had nearly twice the risk of death than those who sat less than 90 minutes at once.
Reasons For Death Unclear
It’s not exactly known how prolonged sitting increases the risk of an early death.
“There is evidence that suggests, but does not prove, that it could be about how our body handles blood sugar,” Diaz said. “We think it’s through a kind of diabetic pathway. When our muscles are inactive, they are not using blood sugar, and we know that blood sugar can wreak terrible consequences on our body.”
Dr. David Alter, associate professor at the University of Toronto, who wrote an editorial published along with the findings, said some scientists think more sitting reduces insulin activity. Others believe “net calorie expenditures” decline as sitting increases. Regardless of why, Alter reiterated the study’s findings. “If we are to sit for prolonged periods at a time — more than 30 minutes at a time, and for many hours per day — more than 12 hours per day, our risk of death is high.”
Of course, as is the case with many studies, these findings do not prove that long periods of sitting causes premature death. It only shows an association between the two. However it is safe to say that being active throughout the day certainly does not hurt.