Sitting Can Cut Life Expectancy. Three Tips for Staying on the Move

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If you’re on the subway, don’t scramble to find a seat. If you’re reading, why not stand up? And if you work in an office, install motion sensors that turn lights on and off.

Those are just three pieces of advice from I-Min Lee, a co-author of a study published Tuesday in the online journal BMJ Open that shows that sitting down for more than three hours a day can cut a person’s life expectancy by two years, even if he or she is physically active and refrains from dangerous habits like smoking.

Watching TV for more than two hours a day can also shave life expectancy by another 1.4 years, according to the report, which analyzed five underlying studies of nearly 167,000 people over a range of four to 14 years.

The study adds to a growing body of evidence that points to the potential consequences of leading a sedentary lifestyle. Last year, scientists found a link between sedentary jobs, or jobs that don’t require a lot of energy expenditure, with colon and rectal cancer. Scientists uncovered similar findings in March, when they found that cancers linked to obesity and lack of physical activity rose every year from 1999 through 2008.

In light of these findings, Dr. Lee, a researcher in the department of epidemiology at the Harvard School of Public Health, recommended that people avoid sitting for prolonged periods of time. In addition to limiting the amount of time you spend watching TV, Dr. Lee offered an interesting tip.

“My office is long in dimension, so the sensor is quite a distance from where I sit. It has been annoying me that the lights go off periodically, since it doesn’t sense me. Maybe that’s a good thing – every so often, I have to go jump up and down to activate the sensor!” she said in an email. And, she added, ”make the sensor less ‘sensitive’ – so it is more apt to make the lights go off.”

And there’s another bonus: “Besides making one get up and move, it’s energy saving,” Dr. Lee said.