Nearly 4% of All-Cause Mortality Linked to Excess Sitting

Sitting for more than 3 hours per day is responsible for 3.8% of all-cause mortality, according to an analysis of behavioral surveys from 54 countries.

Importantly, reducing sitting time to less than 3 hours daily could increase life expectancy by an average of 0.20 years, Leandro Fórnias Machado de Rezende, MSc, from the Department of Preventive Medicine, University of Sao Paulo School of Medicine, São Paulo, Brazil, and colleagues report in an article published online March 23 in the American Journal of Preventive Medicine.

Although previous research has linked excessive sitting time with a number of health concerns, including obesity and metabolic syndrome, and with an increased risk for death from cardiovascular disease and cancer, even among people who exercise regularly, other findings have not supported this conclusion.

In the current analysis, the investigators sought to identify the actual population-attributable fraction (PAF) of all-cause mortality associated with sitting time, and the possible gains in life expectancy in the absence of this risk factor. "PAF is a measure of association used by epidemiologists to quantify and summarize the public health burden due to one risk factor and describes how much an outcome (in this study, all-cause mortality) may be reduced by eliminating an exposure (in this case, sitting time)," the authors explain.

For the investigation, the researchers used data from a published meta-analysis of observational studies in adults, which they matched with statistics on population size, actuarial table, and overall deaths. According to their calculations, "[s]itting time was responsible for 3.8% of all-cause mortality (approximately 433,000 deaths) in 54 countries worldwide," they report.

Moreover, they observed a dose–response relationship between sitting time and all-cause mortality. "[E]ven modest reductions, such as a 10% reduction in the mean sitting time or a 30-minute absolute decrease of sitting time per day, could have an instant impact in all-cause mortality (0.6%) in the...evaluated countries.... [B]older changes (for instance, 50% decrease or 2 hours fewer) would represent at least three times fewer deaths versus the 10% or 30-minute reduction scenarios."

Because physical inactivity is its own risk factor for all-cause mortality, the researchers considered the effect of removing both physical inactivity and sitting time and determined that "about 14% of all deaths per year (more than 1.5 million deaths in these countries) could be avoided." They caution, however, that this estimate assumes independence between physical inactivity and sitting time, "which still requires further research."

The findings point to the importance of promoting increased physical activity and less prolonged sitting to reduce the risk for premature death; however, "changing population levels of sedentary behavior is challenging," the authors concede.

Excessive sitting is common in modern culture and is determined by multiple social and environmental factors, all of which are "strongly influenced by the current economic system, including a greater number of labor-saving devices for commuting, at home and work, and urban environment inequalities that force people to travel longer distances and live in areas that lack support for active lifestyles," the authors state. In this regard, "only interventions aimed at tackling the macro determinants of sedentary behavior will be able to achieve the bolder scenarios assumed in the analysis."

The authors have disclosed no relevant financial relationships.

Am J Prev Med. Published online March 23, 2016.

http://www.ajpmonline.org/article/S0749-3797(16)00048-9/fulltext