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Prolonged sitting increases risk of serious illness and death regardless of exercise, study finds

BMJ 2015; 350 doi: (Published 20 January 2015) Cite this as: BMJ 2015;350:h306
  1. Susan Mayor
  1. 1London

Prolonged sitting is associated with an increased risk of cardiovascular disease, type 2 diabetes, and cancer, regardless of physical activity levels, a systematic review has shown. It recommended that people who think that they exercise enough should be made more aware of the dangers of sitting for long periods.

Current Canadian guidelines recommend that adults take 150 minutes of physical exercise a week in bouts of at least 10 minutes to reduce their risk of cardiovascular disease, type 2 diabetes, and some cancers. But limited information exists on the health effects in people who take the recommended amount of physical activity but also sit for prolonged periods.

Researchers analysed 47 studies that assessed sedentary behaviour and health outcomes independent of physical activity.1 These included 829 917 participants with data on all cause mortality, 551 366 participants with data on cardiovascular disease incidence and mortality, and 744 706 people with data on cancer incidence and mortality.

Results showed that greater sedentary time, assessed as the daily overall time spent sitting down, was associated with an increased risk of all cause mortality (pooled hazard ratio 1.24 (95% confidence interval 1.09 to 1.41), P=0.001). It was also associated with an increased risk of incidence and deaths from cardiovascular disease and a number of cancers. The largest risk was for type 2 diabetes (1.910 (1.642 to 2.222)).

Further analysis showed that the health risks of prolonged sitting were more pronounced in people who did little or no exercise than in those who exercised regularly, but exercise did not completely reduce the risks. Sedentary time was associated with a 30% lower relative risk of all cause mortality in people with high levels of physical activity (1.16 (0.84 to 1.59)) than in those who were not physically active (1.46 (1.22 to 1.75)).

“Our findings suggest that prolonged sedentary time, independent of physical activity, is associated with various deleterious health outcomes. These results reaffirm the need for greater public awareness about the hazards of sedentary behaviours,” said the research group, led by David Alter, of the Institute for Clinical Evaluative Sciences in Toronto, Canada. He recommended that, when sitting for a long period, people should take a one to three minute break every half hour to stand up.

“The implications of these findings are far reaching,” agreed Brigid Lynch and Neville Owen, of the Cancer Epidemiology Centre and the Baker IDI Heart and Diabetes Institute in Melbourne, Australia, in an accompanying editorial.2 “Society is engineered, physically and socially, to be sitting-centric,” they wrote.


Cite this as: BMJ 2015;350:h306


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