Every minute of physical activity contributes to reducing risk of heart attack and coronary death in older adults with limited mobility, says a study.

"Reducing time spent being sedentary even by engaging in low-intensity activities could have important cardiovascular benefits for older adults with mobility limitations," said senior author of the study Thomas Buford from the University of Florida Institute on Aging in Gainesville, Florida.

For the study, the researchers measured movement with accelerometers in 1,170 people aged 74-84 at eight centers across the US who had physical limitations but could walk 400 metres.

Using factors such as age, cholesterol levels and blood pressure, the researchers calculated participants' predicted 10-year risk of heart attack or coronary death.

For every 25-30 minutes a participant was sedentary per day, his/her predicted risk was one percent higher.

Physical activity like slow walking or light housekeeping was linked to higher HDL or high-density lipoprotein ("good") cholesterol levels in people with no history of heart disease.

Participants on an average spent only an hour or less with physical activity such as moderate walking.

Generally, most physical activity recommendations suggest that adults should engage in higher intensity activities to improve or maintain health. But that level might not be realistic for sedentary older adults with limited mobility, researchers said.

"Encouraging individuals to just reduce the amount of time they spend being sedentary may have important cardiovascular benefits," Buford noted.

The study appeared in the Journal of the American Heart Association.