Too much sitting in front of TV may cut life short

* Even people who are not too fat may be at risk

* Cardiovascular death risk seen especially higher

WASHINGTON, Jan 11 (Reuters) - Sitting in front of a television set for hour after hour day after day may raise the risk of death from heart disease and other causes -- even in people who do not weigh too much, Australian researchers say.

Compared with adults who watched less than two hours of TV a day, those who watched more than four hours had a 46 percent higher risk of death from all causes and an 80 percent higher risk of cardiovascular death during the six-year study period.

Each hour spent sitting in front of the TV per day raised a person's risk of death from cardiovascular disease by 18 percent and the risk of cancer death by 9 percent, according to the study appearing on Monday in the American Heart Association journal Circulation.

The study focused on watching television. But the findings suggest that sitting anywhere for extended periods of time -- at a desk or in front of a computer -- may pose a health risk.

Nearly 9,000 Australian adults, average age around 50, were tracked for roughly six years by researchers of the Baker Heart and Diabetes Institute in Victoria.

The increased risk was seen in obese people in the study as well as those with a healthy weight because prolonged periods of sitting have an unhealthy influence on blood sugar and blood fat levels, the researchers said.

"A lot of the normal activities of daily living that involved standing up and moving the muscles in the body have been converted to sitting," the institute's David Dunstan, who led the study, said in a statement.

"For many people, on a daily basis, they simply shift from one chair to another -- from the chair in the car to the chair in the office to the chair in front of the television."

Researchers tracked lifestyle habits of 3,846 men and 4,954 women in Australia divided into three groups: those who watched TV less than two hours per day, those who watched between two and four hours, and those who watched more than four hours.

The negative health effects were seen in the heavy TV watchers regardless of other heart disease risk factors, including smoking, high blood pressure, high blood cholesterol, bad diet and lack of exercise, the researchers reported.

Only a relatively small number of participants, 284 people, died during the study, including 87 from heart disease and 125 from cancer. People with pre-existing heart disease and some others were excluded from the study.

Dr. Tim Chico, a cardiologist at Britain's University of Sheffield, said television provides no health benefit and eats up time that could be better used to get healthier.

"It is ironic that TVs are getting thinner, while we are getting fatter," Chico, who was not involved in the study, said in a statement.

Editing by Maggie Fox and Will Dunham