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October 2012

Are you sitting comfortably?

Kamal Mahtani
Last edited 22nd October 2012

For those interested in the history of medicine you may have heard of Jeremy Morris (1910-2009). Dr Morris was a Scottish epidemiologist who, during the 1950s, was involved in establishing the link between a lack of physical activity and increased cardiovascular risk. In his paper, published in The Lancet, Dr Morris and his colleagues teamed up with London Transport, The Post Office and The Treasury Medical Service. The London Transport Workers Study observed 31,000 men aged 35-64 employed as bus drivers and conductors. They found that you were more likely to suffer from coronary heart disease as a sedentary driver, than as a conductor who climbed the stairs of a double decker bus. This finding also reflected their data in postal workers who were less likely to suffer with coronary heart disease that desk based civil servants. Although a number of limitations of their work were acknowledged, it was clear that a link had been made and in 1996 these contributions were recognized when he was awarded the first International Olympic Committee Prize for Sport Sciences.

Over 60 years later the data linking physical inactivity with ill health continues. Last week researchers at The University of Leicester published a paper on the association between sedentary time in adults and the risk of diabetes, cardiovascular disease and death. They collected data from 18 individual studies. For each one they calculated the risk of ill health associated with the highest sedentary time versus the risk with the lowest, a relative risk (RR). They found a 112% increase in the relative risk of diabetes, a 147% increase in cardiovascular events and a 90% increase in the risk of cardiovascular mortality. With figures like that it’s no wonder the results made the widespread public media. Of the 18 included studies the authors used for their analysis, 13 used TV viewing as their sedentary measure, which was interesting as the authors also stated in their introduction that TV viewing may not be a good representation of total sedentary time, perhaps suggesting it could be an over- or under- estimate. The other 5 studies used self-reporting of sedentary time which is notorious for having poor reliability. That said if someone asked you how much time you sit down in a day, do you think you were more likely to over or under estimate? The other interesting point was that the risk seemed independent upon how much activity you were doing outside the sedentary time. So even if you go to the gym for 1 hour, it’s what you do with the other 23 hours that seem to count as well.

Despite some limitations, the paper adds to the work of Dr Morris and others, supporting the evidence linking physical inactivity and ill health.

Crikey!...even now you might be sitting down and reading this. I better add some handy tips for standing up while sitting.

As for me, I’ve been sitting down and writing this for 40 minutes, time for a stretch I think…

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