(iStock) (FrancescoCorticchia/Getty Images/iStockphoto)

Regular walking may help older adults live longer, even if they don't walk enough to meet exercise guidelines, a new study finds.

According to federal exercise guidelines, adults up to age 64 should get at least 2.5 hours of moderate physical activity per week. But only about half of those adults, and 42 percent of people ages 65 to 74, meet this recommendation, the researchers said.

The new study analyzed information from nearly 140,000 U.S. adults in their 60s, 70s and 80s, and followed them for 13 years. The participants were asked how much time they spent exercising per week and which types of activity they engaged in.

The results showed that those who reported walking regularly but not enough to meet the exercise guidelines were less likely to die during the study period than those who didn't get any physical activity. Specifically, the researchers found that those who didn't get any exercise were 26 percent more likely to die during the study period than were those who walked for less than two hours per week. [Extending Life: 7 Ways to Live Past 100]

The findings held even after the researchers took into account factors that could affect the link, such as smoking, obesity, chronic conditions (including diabetes) and time spent sitting down.

The finding suggests that doctors "should encourage patients to walk, even if less than the recommended amount, especially as they age, for health and longevity," the researchers wrote in the American Journal of Preventive Medicine. "Walking has been described as the 'perfect exercise' because it is a simple action that is free, convenient, does not require any special equipment or training, and can be done at any age," they wrote.

Many studies have found a link between physical activity and an increased life span, but relatively few have looked specifically at walking (separate from other types of exercise), as the new study does, the researchers said.

The study also found that walking for a length of time that meets or exceeds physical activity guidelines was linked to even more benefits. Those who walked for 2.5 to five hours a week were 20 percent less likely to die of any cause, 30 percent less likely to die of respiratory disease and 9 percent less likely to die of cancer during the study period, compared with those who walked for less than two hours a week.

"This study shows that engaging in walking is associated with increased longevity and has the potential to improve the public's health significantly," the researchers concluded.