In recent decades, the amount of time spent in sedentary behaviour has increased significantly, and there is a large body of evidence to suggest that prolonged sitting is associated with increased mortality. Research investigating cause-specific mortality suggests sitting for 6 hours or more is associated with a 19% higher all-cause mortality rate compared with those sitting for less than 3 hours. Causes of death unsurprisingly included cardiovascular disease, stroke and diabetes, but also neurodegenerative disease and nervous disorders.
Such studies are subject to a wide range of confounding factors that are challenging to control for. Individuals who sit for long periods are more likely to snack, and less likely to exercise. It is interesting to note, however, that multiple studies controlling for physical activity still observed an independent effect of prolonged sitting on mortality.
Of course, those not sitting are likely performing minor exercise in the form of everyday tasks, and the effects of such light physical activity has not been studied. However, it is possible that prolonged sitting increases mortality by other, intrinsic mechanisms. Some research has suggested that sedentary time is associated with low grade inflammation after adjustment for exercise (with the caveat mentioned above).
While we still do not fully understand the underlying mechanisms, there is clear evidence from an individual’s standpoint that prolonged sitting is harmful. Finding ways to maintain low levels of physical activity throughout the day may have a significant impact on health and longevity.
Prolonged Leisure Time Spent Sitting in Relation to Cause-Specific Mortality in a Large US Cohort: https://doi.org/10.1093/aje/kwy125
Sedentary Time and Markers of Chronic Low-Grade Inflammation in a High Risk Population: https://doi.org/10.1371/journal.pone.0078350
Sitting time and all-cause mortality risk in 222 497 Australian adults.: doi:10.1001/archinternmed.2011.2174