It's an invisible effect of aging, but one that can be deadly and send you to an early grave. As we grow older, our blood vessels become more constricted and less pliable in response to blood flow, which in turn leads to high blood pressure and clogged arteries.

But now comes word from the University of Colorado in Boulder that moderate exercise helps older adults' blood vessels relax, substantially reducing this effect of aging, reports Reuters Health. That is one reason why exercise lowers the risk of heart attacks and stroke.

And there is good news here. You don't have to be training for a marathon to benefit. Moderate activity, such as taking a walk five times a week, will produce the age-defying results.

The study: Twenty-eight healthy, but sedentary, men were recruited to test the benefits of a regular program of moderate exercise. Of the 28 participants, 13 were in their 20s and 15 were in their 60s. Led by Dr. Christopher A. DeSouza, the research team first conducted a test called plethysmography, which measures blood vessel function in each man's forearm. Generally speaking, the older men's blood vessels were more constricted than those of the younger men. Eight of the older men then embarked on a three-month exercise program, while the rest of the men in both age groups remained sedentary. The moderate exercise program involved walking for an hour, five days a week.

The results: At the end of the three-month study period, those who exercised showed a marked turnaround in blood vessel constriction--so much so that their plethysmography test results looked more like that of the younger men from earlier in the study than the sedentary group of men their own age, reports Reuters Health. This happened even without changes to weight, body fat, blood pressure or other more traditional indicators of heart health.

The takeaway: All the men in this study were confirmed couch potatoes, but just three months of moderate exercise made that much of a difference! Even if the exercise you do doesn't result in weight loss, there are physical improvements you can't see. "It's that old adage, 'It's never too late to start,'" DeSouza told Reuters Health.

The study findings were published in the medical journal Hypertension.