Physical activity could help you avoid an early death if you sit for most of the day

One hour of brisk physical activity a day "eliminates" the increased risk of death associated with life spent mostly sitting - be it at your desk or in your car - according to new medical research. But it won't do much good to completely eliminate the risks associated with long periods of sitting in front of the TV.

According to a report published in The Lancet medical journal, researchers examining the link between "sedentary behavior" and all-cause mortality found that while at least an hour of exercise a day can "eliminate" the health risks associated with spending most of your day sitting, it was not so effective at getting rid of the risks associated with binge-watching.

The team of researchers was led by Professor Ulf Ekelund from the Norwegian School of Sports Sciences and the University of Cambridge and looked at 16 previous studies that had data on the daily sitting time, TV-viewing time and physical activity of over one million men and women.

They analysed the various data for any associations between daily sitting time and physical activity with all-cause mortality, grouping respondents in terms of how active they were, before repeating their analysis using TV-viewing time instead of daily sitting time.

They then looked at mortality rates in follow-up data to see whether physical activity does reduce or eliminate the detrimental health effects of prolonged sitting as many public health bodies believe.

They found that while "high levels of moderate intensity physical activity (i.e., about 60–75 minutes per day) seem to eliminate the increased risk of death associated with high sitting time," high physical activity does not eliminate the risk of sedentary habits associated with TV watching.

Sedentary lifestyles are associated with various health problems such as cardiovascular disease, diabetes, stroke, colon cancer and premature death as well as other conditions such as depression, osteoporosis and obesity.

The American Heart Association notes on its website that sedentary jobs have increased 83 per cent since 1950 with physically active jobs now making up less than 20 per cent of the US workforce. Obesity alone is estimated to cost the US up to US$210 billion per year with the associated job absenteeism costing around US$4.3 billion annually, according to joint research by the Trust for America's Health and the Robert Wood Johnson Foundation.

But a sedentary lifestyle was not tantamount to a high mortality risk as the study found that those who sat for more than eight hours a day (as many office-based workers do) but still did the highest amount of physical activity were still much better off than those who sat for less time but were very inactive.

As expected those who sat for a long time as well as not doing much exercise had a "significantly increased risk of dying during the follow-up (period of research)" and said the increased mortality risk in those who sat for more than eight hours a day and were also the least active was similar to that of smoking and obesity.

The researchers said that as daily sitting time and TV-viewing time capture similar aspects of sedentary behavior, they "expected broadly similar magnitudes of associations from both exposures. Yet the effect of TV viewing on all-cause mortality seemed to be stronger in magnitude."

For TV-viewing time, the results differed in that they showed that high physical activity reduced, but did not eliminate, the mortality risks seen among those viewing TV for five hours or more a day.

The researchers believe that TV watching rather than just sitting down produced different results because of the dietary habits associated with TV watching, such as snacking or having a meal, which could affect people's metabolism.

"The effect of TV-viewing on all-cause mortality seemed to be stronger in magnitude. This difference is congruent with previous observations and might be partly due to differences in the accuracy of reporting these behaviours," the researchers noted.

"However, other explanations are also plausible. TV-viewing typically occurs in the evenings (at least, for the generation represented in the included studies), usually after dinner, and prolonged postprandial sedentary time may be particularly detrimental for glucose and lipid metabolism. It is also plausible that individuals break up their sitting time more frequently during work than when viewing TV, and breaking up sedentary time seems to be beneficial for various cardio-metabolic risk factors.

"Another explanation for the difference observed could be that TV-viewing might be accompanied by snacking behaviours and food advertising on TV might affect eating behaviour. Thus, associated dietary behaviours may explain some of the differences observed."

The researchers said their research results provided "further evidence on the benefits of physical activity, particularly in societies where increasing numbers of people have to sit for long hours for work or transport."

"Our findings indicate that increased sitting time is associated with increased all-cause mortality; however, the magnitude of increased risk with increased sitting time is mitigated in physically active people. Indeed, those belonging to the most active quartile and who are active about 60–75 minutes per day of moderate intensity physical activity seem to have no increased risk of mortality, even if they sit for more than eight hours a day."

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