In 1991, Runner's World published a two-page questionnaire in the June issue asking readers about their running habits and medical histories–as well as their willingness to continue to report that information for years to come. More than 10,000 people filled it out, and nearly 45,000 others responded to the same questionnaire when it was mailed directly to subscribers. Thus was launched the landmark National Runners' Health Study, which would be funded by the National Institutes of Health and overseen by the Department of Energy. Administered from the beginning by Paul T. Williams, Ph.D., a staff scientist in the Life Sciences Division of the Lawrence Berkeley National Laboratory in Berkeley, California, its mission was nothing less than to identify and quantify the myriad ways running affects our health.

Reflecting the demographics of the sport at the time, the male-female split of those original 54,120 respondents was 70-30 (38,292 men, 15,828 women). But in 1999, for a second study group, Williams recruited more women at running events. This effort enlisted nearly 60,000 runners, 54 percent women. (At the same time, he enlisted 42,000 for a National Walkers' Health Study.)

This total of 113,472 runners–including 45,275 marathoners–established the National Runners' Health Study as the world's biggest and best examination of the health benefits of exercise. Williams resurveyed the original respondents in 1997 and the second group in 2007, collecting and analyzing reams of new self-reported data. Over the past two decades, he has published 65 papers that scientifically prove what all runners suspect and perhaps take for granted–that exercise makes people healthier. His work is regularly cited by mainstream media, from The New York Times to WebMD. As Amby Burfoot, the editor of RW when the study first launched, wrote in a blog about Williams: "He tells us more about ourselves than we could possibly learn anywhere else."

Here are a few highlights:

Heart Disease: Runners who exceed government recommendations for aerobic exercise (75 minutes of vigorous exercise per week, equivalent to running about 4.5 to 7.5 miles per week) have a 40 percent lower risk of heart disease and a 40 percent reduced risk of developing high blood pressure. The news is good for cholesterol, too: Those who run more than 50 miles per week have a 20 percent higher level of "good" HDL and five percent less "bad" LDL.

Arthritis: A 2013 Williams report debunked a common myth–that running wrecks your joints. According to the data, runners have about 20 percent lower risk of osteoarthritis and hip replacement than walkers have, probably because running lowers body mass index more effectively than walking. Williams also found that higher-mileage runners (15 to 23 miles per week) have a 16 percent lower risk of osteoarthritis and a 50 percent lower risk of hip replacement than those who run fewer than eight miles per week.

Eye Diseases: No one expected exercise to have an effect on these, but the study revealed that running produces a 35 percent reduced risk of developing cataracts and a 40 to 50 percent reduced risk for macular degeneration.

There are many other compelling, even surprising, conclusions about running's positive effect on the risk of stroke, diabetes, Alzheimer's, and several kinds of cancer, among other afflictions. (Find more here.) In fact, Williams now believes running actually delays the aging process. "The best prescription a doctor can give is for a running shoe," he says. "Paying for running shoes and marathon registrations could actually produce bigger stockholder dividends for insurance companies by lowering health-care costs."

Williams now wants to resurvey all 156,000 participants. Unfortunately, his funding is about to run out, and if it does, the National Runners' Health Study will shut down in the next few months. So, once again, he's asking RW readers for help. Not as respondents–but as supporters. If you're interested in seeing this research continue, send an e-mail to the Secretary of Energy, Dr. Ernest Moniz ([email protected]), Couch to 5K Plan.

Foot Locker XC Results.

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David Willey is the editor-in-chief of Runner's World. Follow him on Twitter @dwilleyRW.