Physical inactivity causes about six to 10 per cent of major non-communicable diseases, including coronary heart disease and type 2 diabetes, and kills around 5.3 million people a year, a new study has claimed.
The study, published in The Lancet, found that physical inactivity -- or people's failure to spend 150 minutes a week doing moderate exercise such as brisk walking for 30 minutes, five days a week -- was responsible for 5.3 million of the 57 million deaths globally in 2008.
A team led by I-Min Lee from Brigham and Women's Hospital and Harvard Medical School in Boston, US, estimated the global impact of physical inactivity on CHD, type 2 diabetes, breast and colon cancer by calculating population attributable fractions -- or how much of the diseases could theoretically be prevented if all people were to become sufficiently active.
They found that some six per cent of CHD cases worldwide are linked to physical inactivity, ranging from 3.2 per cent in Asia to 7.8 per cent in the Mediterranean region.
Similarly, it's responsible for about seven per cent of type 2 diabetes cases, and 10 per cent of breast and colon cancer cases worldwide.
It showed physical inactivity has become a contributor to the burden of disease and shortening of life expectancy similar to tobacco smoking or obesity, the researchers said.
"Removal of physical inactivity had the largest effect on colon cancer, and the smallest on coronary heart disease, in terms of percentage reduction. However, with respect to the number of cases that can potentially be averted, coronary heart disease would have a far larger effect than would colon cancer because of its higher incidence," they said.
"Although the worldwide incidence of coronary heart disease is not readily available, deaths from coronary heart disease can be viewed against colorectal cancer deaths to provide some perspective," they added.
For example, of the 7.25 million deaths from CHD in 2008, physical inactivity accounted for 15,000 preventable deaths in Africa, 60,000 in the Americas, 44,000 in the Mediterranean region, 121,000 in Europe, 59,000 in southeast Asia, and 100, 000 in the western Pacific region.
In contrast, of the 647,000 colorectal cancer deaths in 2008, 1,000 deaths could have been avoided by eliminating physical inactivity in Africa, 14,000 in the Americas, 2000 in the eastern Mediterranean region, 24,000 in Europe, 4,000 in southeast Asia, and 24,000 in the western Pacific region.
Because physical inactivity is unlikely to be completely eliminated, the researchers also calculated the number of theoretically preventable deaths if inactivity decreased by 10 per cent or 25 per cent, translating to some 533,000 and 1.3 million deaths potentially averted worldwide every year.
What is more, the authors said, life expectancy of the world's population would rise by around 0.68 years if physical inactivity were eliminated. This is similar to the effect of eradicating smoking or obesity.
"This summer, we will admire the breathtaking feats of athletes competing in the 2012 Olympic Games," Lee said.
"Although only the smallest fraction of the population will attain these heights, the overwhelming majority of us are able to be physically active at very modest levels which bring substantial health benefits," Lee added.