Physicians' Academy for Cardiovascular Education

High daily levels of physical activity can eliminate the harmful effect prolonged sitting

Ekeland et al., The Lancet 2016 - The Lancet. Published online July 27, 2016. DOI: http://dx.doi.org/10.1016/S0140-6736(16)30370-1

Background

Over time, many observational studies have shown that lack of physical activity is a major risk factor for morbidity and premature mortality. In modern life, sedentary behaviour accounts for the majority of time awake in most adults in high-income countries.

High amounts of sedentary behaviour, often assessed as daily sitting time or time spent viewing TV, have been associated with increased risks for several chronic conditions and mortality [1-3]. But the remaining questions is whether being active enough can attenuate or even eliminate the detrimental association of daily sitting time with mortality.

This is a systemic review and meta-analysis to examine the joint and stratified associations of sedentary behaviour and physical activity with all-cause mortality. Individual data from 16 studies were analysed according to a predefined protocol and included in a harmonised meta-analysis. All studies were prospective cohort studies that had individual exposure and outcome data, and that provided data on both daily sitting or TV-viewing time and physical activity.

Main results

Conclusion

These analyses on data of over 1 million individuals indicate that high levels of physical activity (60-75 min of moderate intensity physical activity per day) appear to eliminate the increased mortality risks associated with prolonged sitting time. Those most active who sat for more than 8 hours daily showed a lower risk of dying during follow-up than those in the least active quartile 9

The effect of TV-viewing on all-cause mortality seemed stronger than that of sitting, and its effect was only attenuated, but not eliminated by high physical activity. One of several plausible explanations may be that TV-viewing typically occurs in the evening (at least for the generation represented in the studies), which may reflect prolonged postprandial sedentary time, which might be particularly harmful for glucose and lipid metabolism. Alternatively sitting time at work may be interrupted more often than sitting while viewing TV, and breaking up sitting time appears beneficial for cardio-metabolic risk factors.

References

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Find this article online at The Lancet