Estimating the Contribution of Inactivity to Mortality Rates

One observation that has emerged in recent years from large epidemiological studies of health and longevity is that greater time spent sitting correlates with a higher risk of death and thus shorter life expectancy. This even seems to be independent of amount of exercise carried out while not sitting, though that aspect of the findings needs further reinforcement to rise to the level of evidence for the more general association between level of inactivity and mortality rates. As for most statistical human studies it is a challenge to move from correlation to understanding the directions and mechanisms of causation, though as ever we can reference the numerous animal studies in which it is shown that increased activity is very definitely a cause of reduced mortality. This latest paper to look at the "chair effect" is more food for thought on the topic. The national differences suggest that this, like most correlations, reflects the operation of numerous interacting environmental factors:

Exercising and not spending so much time on the couch tend to be some of these good intentions. 31% of the worldwide population does not meet the current recommendations for physical activity according to several studies. In addition, a lack of exercise is associated with major noncommunicable diseases and with deaths of any cause - inactivity is the culprit behind 6% to 9% of total worldwide deaths. Today's lifestyle has an impact on these numbers. In fact, various studies over the last decade have demonstrated how the excessive amount of time we spend sitting down may increase the risk of death, regardless of whether or not we exercise. A new study now estimates the proportion of deaths attributable to that 'chair effect' in the population of 54 countries, using data from 2002 to 2011. "It is important to minimise sedentary behaviour in order to prevent premature deaths around the world, cutting down on the amount of time we sit could increase life expectancy by 0.20 years in the countries analysed."

The results reveal that over 60% of people worldwide spend more than three hours a day sitting down - the average in adults is 4.7 hours/day - and this is the culprit behind 3.8% of deaths (approximately 433,000 deaths/year). The highest rates were found in Lebanon (11.6%), the Netherlands (7.6%) and Denmark (6.9%), while the lowest rates were in Mexico (0.6%), Myanmar (1.3%) and Bhutan (1.6%). Spain falls within the average range with 3.7% of deaths due to this 'chair effect'. The authors calculate that reducing the amount of time we sit by about two hours (i.e., 50%) would mean a 2.3% decrease in mortality (three times less), although it is not possible to confirm whether this is a causal relationship. Even a more modest reduction in sitting time, by 10% or half an hour per day, could have an immediate impact on all causes of mortality (0.6%) in the countries evaluated.


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