Old people who are physically active are apt to live longer than their couch-potato peers, and are more likely to maintain their independence, new research from Israel shows.

And people who had been sedentary but became active -- even those who started when they were well into their 80s -- cut their risk of dying and lengthened the amount of time they were able to live on their own, Dr. Jeremy M. Jacobs of Hebrew University Hadassah Medical School in Jerusalem and his colleagues found.

"The take home message is that even among the very old, it never is too late to start exercising," Jacobs noted in an email to Reuters Health. He and his colleagues report the findings this week in the Archives of Internal Medicine.

While the benefits of exercise are clear, there has been little research on physical activity in very old people, Jacobs and his team note. To investigate, they looked at 1,861 people 70 to 88 years old who had been followed for up to 18 years. Those who got at least 4 hours of exercise each week were classified as physically active, while those who got less were considered sedentary.

Among active 70-year-olds, Jacobs and his colleagues found, 15 percent died over the next 8 years, compared to 27 percent of sedentary 70-year-olds. Eight-year mortality was 26 percent for active 78-year-olds, and 41 percent for their sedentary peers. Among 85-year-olds, 3-year mortality was roughly 7 percent for active individuals and about 24 percent for sedentary people.

Being active also increased the likelihood that a person would be able to continue to perform activities like bathing, dressing and eating by themselves; people who were active when they were 78 were nearly twice as likely to maintain independence in their activities of daily living when they reached 85.

The differences remained significant after the researchers adjusted for health problems, how well people functioned independently, and how people rated their own health.

While it's clear that healthier people would also be more likely to be active, Jacobs and his colleagues controlled for several factors related to longevity, such as smoking, heart disease, diabetes, and functional status, the researcher noted.

"Although the list is not exhaustive, it does include the major risk factors, and controlling for these factors allowed us to isolate physical activity as an independent factor in mortality, and not just an indicator of the overall health of the subjects," he said.

The message of his findings for older people, Jacobs said, is to start being active today if you aren't already. "The beauty of our finding is that the benefits of activity were seen with as little as 4 hours a week of gentle activity. That's just over 30 minutes a day."

To stay safe people should start slowly and rest as needed, he added, and anyone with a history of falls or who is concerned that they are unsteady on their feet should seek medical advice before starting to exercise. It's also important, he added, to watch out for traffic and avoid extremes of temperature.

"Walking is my first choice," Jacobs said. "In addition to the physical benefits, the act of getting outside daily, meeting people, interacting with the outside world and changing seasons are all ingredients of successful aging."