SITTING for more than 10 hours a day means you are biologically eight years older, a study found.
Those who sat for extended periods and did little exercise had cells that were biologically older than those who moved around.
Researchers from California University in San Diego studied almost 1500 women aged 64 to 95.
They found those who remained seated for more than 10 hours and completed less than 40 minutes of moderate to physical activity a day were most affected.
These women had shorter telomeres — tiny protective caps found on the ends of DNA strands — that act like the plastic tips of shoelaces.
They guard against deterioration and progressively shorten and fray with age. Shortened telomeres are associated with cardiovascular disease, diabetes and major cancers.
Significantly, the shortening process can be accelerated by lifestyle factors such as obesity and smoking.
Study leader Aladdin Shadyab said people who spend long hours sat at desks or in chairs at home could mitigate some of the damage by exercising.
He added: “Our study found cells age faster with a sedentary lifestyle.
“Chronological age doesn’t always match biological age.
“We found that women who sat longer did not have shorter telomere length if they exercised for at least 30 minutes a day.
“Discussions about the benefits of exercise should start when we are young, and physical activity should continue to be part of our daily lives as we get older, even at 80 years old.”
National UK guidelines suggest adults should do at least 150 minutes of moderate intensity exercise or 75 minutes of vigorous intensity exercise each week.
Health chiefs suggest this can be achieved by doing 30 minutes of moderate intensity exercise five days a week.
They also advise: “All adults should minimise the amount of time spent being sedentary (sitting) for extended periods.”
The participants completed questionnaires and wore an accelerometer on their right hip for seven consecutive days during waking and sleeping hours to track their movements.
The findings were published in the American Journal of Epidemiology.
Future studies will examine how exercise relates to telomere length in younger people and men.
Previous studies have suggested men who adopt a sedentary lifestyle may be less at risk of disease than women.