Active older people may reduce their risk of a heart attack if they increase their activity levels as they age, a new study suggests.

According to US and Portuguese scientists, people over the age of 65 should ‘not slow down' as they get older.

They monitored the progress of almost 900 adults with an average age of 71. Heart monitor recordings were taken 24 hours a day over a five-year period.

The study found that those who walked more and at faster speeds had fewer irregular heart rhythms and a healthier heart rate than those who were less active.

"These small differences are influenced by the health of the heart and the nervous system that regulates the heart. Early abnormalities in this system are picked up by changes in heart rate variability, and these changes predict the risk of future heart attacks and death," the scientists said.

Not surprisingly perhaps, the study found that the more physically active people were, the healthier their heart rate. However, it also found that those who increased their walking pace or distance during the study period had a healthier heart rate than those who cut down on walking or reduced their pace.

"Any physical activity is better than none, but maintaining or increasing your activity has added heart benefits as you age. Our results also suggest that these certain beneficial changes that occur may be reduced when physical activity is reduced," the scientists said.

They estimated that the most physically active older people have an 11% reduced risk of suffering a heart attack or sudden cardiac death compared to the least active.

"So if you feel comfortable with your usual physical activity, do not slow down as you get older - try to walk an extra block or walk at a faster pace and if you're not physically active, it is never too late to start," the scientists said.

Details of these findings are published in the journal, Circulation.