We've been taught that exercise at any age is beneficial to good health and longevity, but recent research has zoomed in on a time period in your life when it may the most important of all.

Researchers from the University of Mississippi and the University of California, San Francisco looked at telomere data — those are the caps at the end of DNA strands that are linked to longevity — from 6,500 adults based on a national survey. They found that exercise prevented telomere shrinkage and prolonged life in those ages 40 to 65.

In fact, the more exercise this group did — walking, cycling, weight lifting and the like — the less their telomeres, and their life spans, shrunk.

It's unclear whether exercise directly prevents telomeres from shrinking, but researchers have established a strong tie between working out and the genetic markers thought to correspond with life span.

"Exercise is important at any age, and the younger you begin working out, the easier it is to remain physically active throughout your life," says Andrea Klemes, chief medical officer at MDVIP, a network of preventive medicine and primary care physicians in Boca Raton, Florida.

"However, training as an adult can help reduce the risk of chronic diseases and injuries and helps us maintain our physical and cognitive function. And since many people begin to realize the effects of the aging when they hit middle age — such as feeling stiffer, fatiguing quicker, gaining weight, losing muscle mass and weakening of bones — being physically active at age 40 and older becomes an important component of performing many activities of daily living and maintaining quality of life."

Keeping the immune system young

In a 2018 study, researchers from the University of Birmingham and King's College London found that older adults (ages 55 to 79) with years of regular exercise apparently age more slowly than healthy adults who don't exercise regularly.

The long-term exercisers didn't lose muscle mass or strength over time, the study found, nor did their body fat or cholesterol increase with age. Men's testosterone levels also stayed high, suggesting they "may have avoided most of the male menopause," according to a statement about the study. And perhaps most surprisingly, the immune systems of regular exercisers didn't seem to age, either.

"We hope these findings prevent the danger that, as a society, we accept that old age and disease are normal bedfellows and that the third age of man is something to be endured and not enjoyed," says study co-author and University of Birmingham researcher Niharika Arora Duggal.

Longer telomeres, longer life

And in another large study from the National Cancer Institute in Bethesda, Maryland, researchers showed that those who exercised for 450 minutes per week, or a little more than an hour per day, were 39 percent less likely to die prematurely than people who never exercised.

"These telomeres shorten with time, and shorter telomeres are generally associated with illness, cancer and other disease. So it is not surprising that scientists all over the world are obsessed with trying to determine what can lengthen these telomeres," says Darshi Shah, a nutritional therapist and health coach.

Shah believes that deep meditation, of which she is an advocate, and diet also lengthen telomeres. "It is generally accepted in the health coaching industry that a specific diet high in (G.O.M.B.B.S.) greens, onions, mushrooms, beans, berries and seeds and is plant-based seems to be anti-aging, anti-disease and boost immunity."

The bottom line seems to be that shorter telomeres suggest cellular aging and shorter life spans, while exercise, especially once you're over 40, prevents those telomeres from shortening, extending your life.

When telomeres becomes too short, they fray, which stops a cell from dividing. "Scientists also identified exercise as a method of slowing telomere fraying, making physical activity one of the most important lifestyle behaviors someone 40 and older should adopt and/or continue," says Klemes.

It's time to put on your workout gear and get moving.

Editor's note: This article has been updated with new information since it was originally published in December 2015.

Exercise after 40 may be the most crucial
Proper exercise may lengthen telomeres, which are linked to longevity.