Physical activity can eliminate death risk related to prolonged sitting, but not death risk related to high TV-viewing time

prolonged sitting

Long sitting time has long been found to be associated with increased risk of death. In a seminal 1953 Lancet paper, researchers reported a higher risk of heart disease in London bus drivers compared with conductors.

Estimates from 2002 showed that lack of physical activity caused 5,000,000+ deaths each year in the world. Lack of physical activity can increase the risk of heart disease, stroke, type 2 diabetes, early death, and some cancers.

Despite the harmful effects of prolonged sitting, many people spend their daytime sitting in the office in front of computers. When they go home, they may watch TV for a long time. This is especially obvious in high-income countries.

One important question is: if one takes enough physical activity every day, will this reduce or even eliminate the death risk from long sitting time?

To answer this question, researchers conduct a meta-analysis of data from more than 1 million men and women. The finding is recently published in The Lancet.

The data collected by 13 studies included daily sitting or TV-viewing time and physical activity, and also reported death caused by heart disease, cancers, and other causes.

The 13 studies recruited 1,005,791 participants who were followed up for 2-18 years. About 8.4% died during the time. Compared with the most active people (who sat < 4 h/day and had physical activity > 35 h/week), people who had physical activity < 16 h/week had 12-59% higher ratio of death.

In the most active people, daily sitting time was not related to their death ratio. This might be because their overall sitting time was quite short.

Importantly, in people who sat > 8h/day but also had physical activity > 35 h/week, sitting time was not related to their death ratio. By contrast, in people who sat the least (< 4h/day) and moved the least (physical activity < 2.5 h/week), the risk of dying significantly increased.

Furthermore, watching TV > 3 h/day was related to higher death risk regardless of physical activity, except in the most active people (physical activity > 35 h/week), where death risk was increased only when viewing TV > 5 h/day.

These findings suggest that if people take sufficient physical activity (60-75 min/day), prolonged sitting will not increase the death risk. However, physical activity cannot eliminate the increased death risk associated with longer TV time.

Citation: Ekelund U, et al. (2016). Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet. pii: S0140-6736(16)30370-1. doi: 10.1016/S0140-6736(16)30370-1.
Figure legend: This image is for illustrative purposes only.