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One hour of physical activity offsets increased risk of death from sitting

About 60 to 75 minutes of moderate intensity physical activity negated the increased risk for death associated with sitting for 8 hours each day, according to findings published in The Lancet.

Ulf Ekelund, PhD, professor at the Norwegian School of Sport Sciences, in Oslo, and colleagues also reported that this level of activity mitigates, but does not completely offset, the increased risk for death associated with long periods of watching television.

"Sedentary behaviors are highly prevalent, and data from adults in high-income countries suggest the majority of time awake is spent being sedentary," Ekelund and colleagues wrote. "Further, high amounts of sedentary behavior, usually assessed as daily sitting time or time spent viewing TV, have been associated with increased risks for several chronic conditions and mortality. A crucial question is: If one is active enough, will this attenuate or even eliminate the detrimental association of daily sitting time with mortality?"

The researchers identified 16 prospective cohort studies that analyzed TV-viewing time or sitting time and physical activity and their effects on all-cause mortality, cardiovascular disease mortality, or colorectal, colon and breast cancer mortality. They conducted a meta-analysis of these studies, stratifying physical activity, sitting time and TV-viewing time into several groups and measuring associations with all-cause mortality. Activity was reported in metabolic equivalent of task (MET)-hours per week.

The sitting studies followed 1,005,791 participants for 2 to 18 years; 84,609 (8.4%) of the participants died during the follow-up period.

Results showed that the mortality rates for participants who had more than 16 MET-hours per week and were sitting more than 4 hours per day (HR = 1.12; 95% CI, 1.08-1.16) and for participants who had less than 2.5 MET-hours per week and were sitting more than 8 hours per day (HR = 1.59; 95% CI, 1.52-1.66) were 12% to 59% higher than for participants who were sitting less than 4 hours per day and had more than 35.5 MET-hours per week.

In the most active participants, daily sitting time was not associated with increased all-cause mortality.

Researchers found no increased mortality risk in participants who sat more than 8 hours each day and also reported more than 35.5 MET-hours per week of activity (HR = 1.04; 95% CI, 0.99-1.1) when compared with the control group.

In comparison, participants who sat less than 4 hours each day, but reported the lowest level of activity at less than 2.5 MET-hours each week had an increased risk for mortality (HR = 1.27; 95% CI, 1.22-1.31).

The TV-viewing studies followed 465,450 participants; 43,740 of the participants died during the follow-up period.

The researchers reported that sitting and watching 3 or more hours of TV each day was associated with an increased risk for mortality in all activity groups except the most active. In this group, mortality only increased in participants who watched 5 or more hours of TV each day (HR = 1.16, 1.05-1.28).

"There has been a lot of concern about the health risks associated with today's more sedentary lifestyles," Ekelund said in a press release. "Our message is a positive one: It is possible to reduce — or even eliminate — these risks if we are active enough, even without having to take up sports or go to the gym."

He concluded: "For many people who commute to work and have office-based jobs, there is no way to escape sitting for prolonged periods of time. For these people in particular, we cannot stress enough the importance of getting exercise, whether it's getting out for a walk at lunchtime, going for a run in the morning or cycling to work. An hour of physical activity per day is the ideal, but if this is unmanageable, then at least doing some exercise each day can help reduce the risk."

Pamela Das, PhD, senior executive editor of The Lancet, and Richard Horton, MBBS, editor-in-chief of The Lancet, wrote in a comment that this study, along with several others published in the series, should "help shift the current focus on reducing sitting times alone to more emphasis on regular activity."

"The world needs to get serious about physical activity," they wrote. "And that means money — for capacity in public health departments to undertake adequate surveillance, cross-sector partnerships, interventions, policy monitoring, and research, especially the cost-effectiveness of interventions. There is extensive evidence about the need for action to improve physical activity, what actions are most promising, and who needs to be involved."

Das and Horton hope that the series will push people to become more active and policy makers to take physical activity more seriously.

They concluded: "We must continue to strive towards the longer term goal: The integration of physical activity into our daily lives." – by Chelsea Frajerman Pardes

Disclosures: The researchers report no relevant financial disclosures.