Six hours TV a day takes years off your life

Television kills – or at least it shortens your life by 22 minutes for every hour you spend glued to the screen.

The unexpectedly lethal impact of watching the box is revealed as latest figures suggest we are spending more time in front of the screen than ever. Viewing rates hit a new high in the first half of 2011, averaging four hours and three minutes a day, according to the TV marketing body Thinkbox.

Television watching is a sedentary activity which is known to be harmful to health and is distinct from getting too little exercise. But a new study suggests its damaging effects may even rank alongside those from smoking and obesity. The study includes bad news for advertisers: it found that if you get up during the commerical breaks and run around, you may be able to ameliorate television's worst effects.

Researchers who studied television viewing habits in Australia calculated that people who watch for an average of six hours a day shorten their life expectancy by almost five years.

They based their calculations on data on the link between television viewing and death from the Australian diabetes, obesity and lifestyle study which involved 11,000 adults aged 25 and over. Applying these findings to the whole population over 25, who are estimated to have watched 9.8 billion hours of TV in 2008, they concluded that it accounted for 286,000 years of life lost – equivalent to 22 minutes for each hour watched. By comparison, smoking one cigarette is estimated to shorten life expectancy by 11 minutes – equivalent to half an hour of TV watching.

Writing in the British Journal of Sports Medicine, the authors from the University of Queensland, say the figures suggest "substantial loss of life may be associated with prolonged TV viewing." The UK and other industrialised countries are likely to be similarly affected "given the typically large amounts of time spent watching TV and the similarities in disease patterns." The researchers add: "if these figures are confirmed and shown to reflect a causal association, TV viewing is a public health problem comparable in size to established behavioural risk factors."

Some respite is offered by a second study, published in The Lancet, suggesting just 15 minutes of physical activity a day increase life expectancy by three years. Researchers from Taiwan who studied medical screening results for 400,000 people found even those who did as little as 92 minutes' exercise a week – equivalent to 15 minutes a day for six days a week – reduced their risk of death by 14 per cent. Even this minimal amount of exercise could postpone one in six of all deaths – similar to the effects of a stop-smoking programme. Each additional 15 minutes a day reduced the death rate by a further 4 per cent.

A spokesperson for the British Heart foundation said: "Many of us make a conscious decision not to smoke because we know it's bad for us, and this study suggests that more of us should make the same kind of pledge about lounging around and watching TV. It's good to relax for a while, but this study supports the view that too much of it can be bad for our health."