Sitting more than four hours a day could raise risk of dying early: Study

By Dr. Ananya Mandal, MDMar 29 2012

According to Australian researchers spending less time sitting could boost longevity. Their study of more than 220,000 NSW residents found the longer you spend sitting down the greater your risk of dying early, even if you otherwise do regular exercise.

Professor David Dunstan, from the Baker IDI Heart and Diabetes Institute, said health workers usually focused on trying to increase people's participation in sports, and trying to get them to do at least half an hour of exercise every day. “We need to think more about what we do with the 15 hours of non-exercise wake time,” he said. He explained that sitting can be detrimental for our health because when we sit down there is an absence of muscle contractions. These contractions are required for the body to clear blood glucose and blood fats from the blood stream.

Studies on animals have shown that when the body stops moving for long periods of time it slows down one of the key enzymes needed to break down blood fats. The study, published in the Archives of Internal Medicine, found adults who sat for more than 11 hours a day had a 40 per cent increased risk of dying within three years, compared with those who sat for fewer than four hours a day. People who sat for eight to 11 hours a day increased their risk of dying by 15 per cent.

Dr Hidde Van Der Ploeg from Sydney University, the lead author of the study, said research into the health effects of sitting usually put the blame on sedentary activities such as television watching. Instead, they looked at the total sitting time throughout the day regardless of the type of activity. The team looked at questionnaire data from the respected 45 and Up Study and data from the NSW's Registry of Births, Deaths & Marriages. They found more than 5,000 participants died within three years, and about 7 per cent of those deaths could be attributed to prolonged sitting time.

“Doing at least 30 minutes of physical activity each day is still important but it's just as critical for people to reduce their sitting time,” Dr Van Der Ploeg said. He said the average adult spends 90 per cent of their leisure time sitting down. “We sit while eating our breakfast, we sit as we drive, we sit behind our desk all day, we're always sitting down and this is a health risk.” Professor Dunstan said the modern, urban environment was conducive to sitting behaviors. “We need to take those opportunities to stand up, while on transport, at work, during our leisure time,” he said.

He acknowledged that sitting for less than four hours a day was no mean feat. “It will require people to drastically change, which is hard,” he said. “But that's the goal.” The findings were consistent across all age groups, sexes, body mass index categories and physical activity levels.

The link between prolonged sitting as a health hazard was noted as early as the 17th century by the occupational physician Ramazzini. Half a century ago, a British study also showed that workers who were required to sit for long periods of time, such as bus drivers, had higher incidences of cardiovascular disease compared with workers who were required to stand, such as postal workers.

The research was commissioned by the Cardiovascular Research Network and supported by the National Heart Foundation Australia's NSW Division.

Heart Foundation CEO Tony Thirlwell said being inactive was a major risk factor for cardiovascular disease, which is responsible for over 17 million deaths a year worldwide.  “Watching TV, using computers and electronic games can involve sitting for long periods and have become a big part of leisure time,” he said. “But we know that people who spend less time on these things have better health than those who spend too much time on them.”