A new study of over 1 million people finds that doing at least one hour of physical activity per day, such as brisk walking or cycling for pleasure, may eliminate the increased risk of death associated with sitting for 8h a day.
Physical inactivity is linked to an increased risk of heart disease, diabetes and some cancers and is associated with more than 5 million deaths per year  and, as the first global economic analysis of physical inactivity shows, costs the world economy over US$67.5 billion per year in health care costs and lost productivity.
The findings come from a new four-paper Series published today in The Lancet and launched in London ahead of the Summer Olympic Games. The authors of the Series warn there has been too little progress in tackling the global pandemic of physical inactivity since the 2012 Olympics, with a quarter of adults worldwide still failing to meet current recommendations on physical activity.
Sitting time, physical activity and risk of death (paper 1)
Researchers analysed data from over 1 million people from 16 studies. The research team wanted to see how many hours of daily physical activity would be required to eliminate the association between prolonged sitting time and increased risk of death. Examples of physical activity were brisk walking at 5.6 km/h or cycling for pleasure at 16 km/h.
The researchers classified individuals into four equally sized groups according to how active they were - less than 5 mins a day for the least active, up to 60-75 mins a day for the most active .
People who sat for 8 hours a day but were physically active had a much lower risk of death compared to people who sat for fewer hours a day, but were not physically active (figure 2A). This suggests that physical activity is particularly important, no matter how many hours a day are spent sitting. In fact, the increased risk of death associated with sitting for 8 hours a day was eliminated for people who did a minimum of 1 hour physical activity per day. The greatest risk of death was for people who sat for long periods of time and were inactive.
WHO guidelines recommend that adults should do at least 150 mins of physical activity per week , which is much lower than the 60-75 mins per day identified in this analysis. The study also warns of the progress that remains to be made in increasing levels of physical activity since only about 25% of people in the analysis did an hour or more physical activity per day.
"There has been a lot of concern about the health risks associated with today's more sedentary lifestyles," says lead author Professor Ulf Ekelund, the Norwegian School of Sports Sciences, Norway and the University of Cambridge, UK "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 adds: "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." 
The research team also looked at time spent watching TV per day - a specific type of sedentary behaviour - in a subgroup of approximately half a million people. They found similar results: sitting watching TV for over 3h per day was associated with an increased risk of death in all activity groups, except the most active (figure 2B). The authors stress that the association is likely not because of a causal link between watching TV and an increased risk of death, but simply that watching TV is a specific type of sedentary behaviour. The increased risk of death associated with sitting watching TV for many hours a day was slightly greater than the increased risk of death associated with total sitting time. The authors say that this could be due to a number of factors - for instance, long hours watching TV may be a marker of a more unhealthy lifestyle in general including being less likely to take exercise. Also, because people usually watch TV in the evenings after dinner which might affect their metabolism, or because people may be more likely to snack while watching TV.
The authors warn that the study mainly included data from people aged over 45 years old from the USA, Western Europe and Australia, so may not apply to other populations.
Economic burden of physical inactivity (paper 2)
In the first study to estimate the global economic burden of physical inactivity, researchers estimated the total cost of physical inactivity to be at least INT$67.5 billion in 2013  - equivalent to what US$67.5 billion could buy in the United States in 2013, or the total Gross Domestic Product of Costa Rica in the same year. In the USA alone, the economic burden of physical inactivity in 2013 was US$27.8 billion, compared to R$3.3 billion in Brazil, £1.7 billion in the UK and AUS$805 million in Australia.
The study found that high-income countries bear a much larger proportion of the economic burden associated with physical inactivity (80.8% of health-care costs in high income countries and 60.4% of indirect costs), whereas low-income and middle-income countries have a larger proportion of the disease burden (75.0% of the global burden of disease for physical inactivity is borne by low and middle income countries) (table 3).
"The current economic cost of physical inactivity is borne mainly by high income countries. However, as low and middle income countries develop, and if the current trajectory of inactivity continues, so too will the economic burden in low and middle income countries who are currently poorly equipped to deal with chronic diseases linked to physical inactivity," says lead author Dr Melody Ding, University of Sydney, NSW, Australia. "Our study makes the economic case for a global response to promote physical activity to tackle diseases such as diabetes, heart disease and some cancers, with the aim of reducing health inequalities." 
The authors note that the study only included costs for the five major diseases associated with physical inactivity (coronary heart disease, stroke, type 2 diabetes, breast cancer, and colon cancer), therefore the cost calculations are based on conservative estimates, and the true cost may be even higher.
Progress since the 2012 Olympic Games (paper 3)
Although there has been progress in developing national policies, the authors found these were too often not being put into practice. In 2010, 75% of countries reported having a physical activity policy but only 44% reported it being operational. In 2015, over 90% had a policy and 71% reported it being operational (figure 2). But there has been little progress in increasing levels of physical activity with 23% of the global adult population and 80% of school-going adolescents failing to meet the WHO recommendation of 150 minutes of moderate-intensity exercise per week in 2015.
"In the past four years, more countries have been monitoring progress in physical activity, but evidence of any improvements is scarce. We know that physical inactivity is linked to diseases including heart disease, diabetes and some cancers, and new evidence also shows that 300000 cases of dementia could be avoided annually if all people were physically active. The global pandemic of physical inactivity remains, and the global response has been far too slow" says lead author Professor Jim Sallis, University of California San Diego, San Diego, CA, USA .
Smarter approaches to physical activity (paper 4)
Increasing levels of physical activity will require collaboration between schools, urban planning, transport, sports and recreation and the environmental sectors, and greater efforts should be made to actively monitor physical activity as a risk factor in clinical practice. The authors point to several successful examples such as the Bus Rapid Transit (BRT) System introduced in Curitiba (Brazil), Bogota (Colombia) and Cambridge (UK) which puts stops further apart than traditional bus stops to encourage walking; or the Coordinated Approach to Child Health (CATCH) in the USA which promotes a healthy school environment including physical activity, food, nutrition and sun protection (see panels 1, 2, 3).
"Large-scale problems require large-scale solutions, and we need commitment from governments, as well as international organisations 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 Professor Rodrigo Reis, Washington University in St Louis, St Louis, MO, USA .
Writing in a linked Comment, Dr Pam Das, Senior Executive Editor and Dr Richard Horton, Editor-in-chief of The Lancet say: "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 remains insufficient because physical activity is not taken seriously enough to rise to the top of the funding priorities."
NOTES TO EDITORS:
 Findings come from The Lancet Physical Activity Series 2012 http://www.thelancet.com/series/physical-activity
 Physical activity was expressed in metabolic equivalent of task (MET)-hours per week. The four quartiles were 2·5 MET-h per week (equivalent to about 5 min of moderate intensity activity per day), 16 MET-h per week (25-35 min per day) and 30 MET-h per week (50-65 min per day), and 35·5 MET-h per week (60-75 min per day).
 Quotes direct from authors and cannot be found in the text of the Articles
 Estimates are provided in International Dollars (INT$) which corresponds to the cost adjusted for purchasing power in the USA in 2013. It is widely used in economics to compare costs in different countries over time. Table 1 provides costs for 142 countries in INT$.