Sitting for at least 3 hours daily is accountable for 3.8% of all-cause deaths, according to researchers.
But it's not all bad news; the study also found that we can increase life expectancy by an average of 0.2 years by reducing sitting time to less than 3 hours a day.
Lead researcher Leandro Rezende, of the Department of Preventive Medicine at the University of Sao Paulo School of Medicine in Brazil, and colleagues publish their findings in the American Journal of Preventive Medicine.
On average, Americans spend up to 13 hours a day sitting, with around 7.5 hours spent sitting at work, which researchers claim can wreak havoc on health.
Last January, for example, Medical News Today reported on a study that suggested prolonged sitting can increase the risk of heart disease, diabetes, cancer and premature death, regardless of physical activity status.
And a more recent study found that, for heart disease patients, sitting for long periods can worsen health, even if they are active.
Despite such evidence, Rezende notes that modern-day demands make changing sitting habits challenging.
"Although sitting is an intrinsic part of human nature, excessive sitting is very common in modern societies," he notes.
"Sedentary behavior is determined by individual, social and environmental factors, all strongly influenced by the current economic system, including a greater number of labor-saving devices for commuting, at home and work, and urban environment inequalities that force people to travel longer distances and live in areas that lack support for active lifestyles."
However, Rezende and colleagues believe their findings highlight the importance of reducing sitting time in order to increase life expectancy.
Life expectancy increased with modest reduction in sitting time
The team analyzed 2002-2011 behavioral survey data of more than 1.1 billion adults over 54 countries - representing around 25% of the global adult population, including American, European, Eastern Mediterranean, Southeast Asian and Western Pacific populations.
- 86% of Americans report sitting for the entire work day
- However, 67% of Americans say they hate sitting
- Every 2 hours spent sitting reduces blood flow, raises blood sugar and reduces "good" cholesterol levels by 20%.
The researchers used the data to assess the sitting time for each population, and these data were compared with national statistics on population size, life table - the probability that a person is likely to die before their next birthday - and all-cause mortality.
The team calculated that, over the 54 countries, a sitting time of 3 hours or more each day was responsible for around 3.8% - or 433,000 - of all-cause deaths, with sitting time having the biggest impact on mortality in the Western Pacific region.
However, they found that reducing sitting time - even slightly - had an immediate impact on rates of all-cause mortality across all countries; life expectancy could be increased by 0.2 years if sitting time was reduced to less than 3 hours daily, regardless of physical activity.
"It was observed that even modest reductions, such as a 10% reduction in the mean sitting time or a 30-minute absolute decrease of sitting time per day, could have an instant impact in all-cause mortality in the 54 evaluated countries, whereas bolder changes (for instance, 50% decrease or 2 hours fewer) would represent at least three times fewer deaths versus the 10% or 30-minute reduction scenarios," explains Rezende.
Findings 'support the importance of promoting active lifestyles'
The team believes the study provides further evidence that prolonged sitting is bad for health, but that reducing sitting time even by a modest amount can reduce its effect on all-cause mortality and may even encourage physical activity.
"Although sitting time represents a smaller impact compared with other risk factors, reducing sitting time might be an important aspect for active lifestyle promotion, especially among people with lower physical activity levels," says Rezende.
"In other words, reducing sitting time would help people increase their volumes of physical activity along the continuum to higher physical activity levels." He adds:
"The present findings support the importance of promoting active lifestyles (more physical activity and less sitting) as an important aspect for premature mortality prevention worldwide, and therefore the need for global action to reduce this risk factor."
Earlier this year, MNT reported on a study suggesting that sit-stand desks - hailed as a useful tool to reduce sedentary behavior - may improve student cognition.