Similarly, if we cut daily TV viewing down to two hours we could add on 1.4 years, they say in a report for the online journal BMJ Open.
But experts say the US estimates, which are based on five separate population studies, are too unreliable to predict personal risk.
Plus the targets are unfeasible.
Prof David Spiegelhalter, an expert in risk calculations at the University of Cambridge, said: “This is a study of populations, and does not tell you personally what the effect of getting off the sofa might be.
“It seems plausible that if future generations moved around a bit more, then they might live longer on average.
“But very few of us currently spend less than three hours sitting each day, and so this seems a very optimistic target.”
It would be challenging to have a desk or computer job and be on your feet for 5 of the 8 hours per day. I’d like to try it. I’ve said for years that we are not intended to sit and type. Computers need to function with us as we move around.
And therefore, I’m going on vacation. Starting tomorrow, no more work. No more desk. I’m going to hike, walk and jog for at least 6 hours a day for the entire next week. Well, I’ll probably sit down here and there to blog from the road.
If you have a computer job and manage to be on your feet while getting your work done, let us know how you do it.