A typical day for many people includes at least 8 hours of sitting - driving to work, sitting in an office, driving home, and watching TV. An international study of over 1 million people shows that 1 hour of moderate physical activity can eliminate the health risks associated with sedentary behavior.
The study forms the first part of a four-paper series published by The Lancet that provides an overview and update of worldwide trends of physical activity and the global impact of physical inactivity.
The first series observing physical activity was released in 2012 ahead of the Summer Olympic Games. The study authors caution that there has been little progress in tackling the global pandemic of physical activity since the 2012 Olympics, with a quarter of adults worldwide failing to meet physical activity recommendations.
In the analysis, the researchers posed the question: Does exercise reduce or eradicate the harmful effects - including increased risk of early death - that are associated with prolonged sitting?
Health risks that are linked to physical inactivity include an increased risk of heart disease, stroke, type 2 diabetes, and some cancers, with recent estimates suggesting that more than 5 million people die each year globally due to failing to meet daily activity levels.
Total worldwide cost of physical inactivity at least $67.5 billion
Findings from the second part of the series - a world-first study to estimate the economic burden of physical inactivity worldwide - shows that globally in healthcare expenditure and lost productivity, physical inactivity cost the world $67 billion in 2013.
"Physical inactivity is recognized as a global pandemic that not only leads to diseases and early deaths, but imposes a major burden to the economy," says Dr. Melody Ding, senior research fellow at The University of Sydney's School of Public Health, Australia.
Dr. Ding notes that if no action is taken to improve population levels of physical inactivity, the economic burden of physical inactivity is projected to increase globally, predominantly in low- and middle-income countries.
The World Health Organization (WHO) recommend that adults aged 18-64 should do at least 150 minutes of moderate-intensity aerobic physical activity throughout the week.
In the first paper of the series, the researchers analyzed 16 studies, which included data from over 1 million people.
The team formed four groups of individuals based on their level of moderate-intensity exercise, ranging from 5-75 minutes per day. Moderate-intensity exercise was defined as walking 3.5 miles per hour or cycling at 10 miles per hour.
1 hour of exercise daily can mitigate risks of early death
Results from the study show that people that spend 8 hours a day sitting but are physically active have a significantly lower risk of death than people who spend fewer hours sitting, but who are not physically active.
Moreover, the increased risk of death associated with spending 8 hours sitting was eliminated by 1 hour of physical activity per day.
People who had the greatest risk of death were those individuals who sat for prolonged periods and were mostly inactive. They were between 28-59 percent more likely to die early, compared with those in the most active group, which is a similar risk to that associated with smoking and obesity.
The study finds that only around 25 percent of participants did an hour or more exercise per day.
"There has been a lot of concern about the health risks associated with today's more sedentary lifestyles," says Prof. Ulf Ekelund, of the Norwegian School of Sports Sciences, Norway, and the Medical Research Council Epidemiology Unit at the University of Cambridge, United Kingdom.
"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."
Prof. Ulf Ekelund
"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," he adds.
Watching TV for long durations raised death risk in most activity groups
Also observed in the study was time spent watching TV per day - a particular type of sedentary behavior - in a subgroup of approximately half a million people.
Watching TV for 3 hours per day was associated with an increased risk of death in all activity groups, except among the most active. The authors say that this association could be because long hours watching TV may be a marker of a more unhealthy lifestyle in general, including being less likely to take exercise.
In a third paper in the series looking at the progress and challenges in physical activity since the 2012 Olympics, Prof. Jim Sallis, of the University of California-San Diego, says: "The global pandemic of physical inactivity remains, and the global response has been far too slow."
Public health challenge of inactivity needs more collaboration
The fourth and final paper highlights the need for collaboration between schools, transport, sports, and recreation and environmental sectors to increase levels of physical activity and monitor physical inactivity as a risk factor for negative health impacts.
"Large-scale problems require large-scale solutions, and we need commitment from governments, as well as international organizations to tackle the global public health challenge of physical inactivity. Science and practice are providing important evidence, but now is the time for action," says Prof. Rodrigo Reis, of Washington University in St Louis, MO.
Dr. Pam Das, senior executive editor, and Dr. Richard Horton, editor-in-chief of The Lancet, say in a linked comment: "The world needs to get serious about physical activity. 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. But capacity and funding remain insufficient because physical activity is not taken seriously enough to rise to the top of the funding priorities," they conclude.