It seems almost counterintuitive that running wouldn't eventually lead to some form of joint injury or degeneration. Some key recent studies however, suggest that runners are at no greater risk of knee injury than non-runners.
The conventional wisdom of running equals bad knees actually had some scientific validation in the form of a 1999 study, showing that women who actively participated in heavy physical sports as teenagers had higher-than-average risk of developing hip osteoarthritis.
The past few years of research on the subject shows a different picture. Not only is there no connection between running and joint injury, but running and other vigorous activity may even be protective of the joints.
Let's go over the literature:
A Stanford University study, published in the Archives of Internal Medicine (2008), by author James Fries, found there was no correlation between running and knee injury, and also that it didn't matter how much the runners ran, whether they averaged 200 or 2000 miles per year.
The study also highlighted that the runners experienced less physical disability, and had a 39% lower mortality rate than the non-runners.
Other studies have shown similar results, for example:
In 2007, a nine-year study of 1,279 elderly residents of Framingham, Mass., found that the most active people had the same risk of arthritis as the least active (Effect of Recreational Physical Activities on the Development of Knee Osteoarthritis in Older Adults of Different Weights:, David T. Felson et. al. Arthritis Care & Research, February 2007; (DOI: 10.1002/art.22464).
Australian researchers, writing in the journal Arthritis and Rheumatism, found that people who exercised vigorously had thicker and healthier knee cartilage compared with their sedentary peers. That suggests the exercisers may have also enjoyed a lower risk of osteoarthritis, which is caused by breakdown and loss of cartilage.
Here is a more recent study on long distance running and knee osteoarthritis. And, for a comprehensive review of the literature, read this very thorough analysis: Exercise and Knee Osteoarthritis: Benefit or Hazard?
Preventing Joint Injury: Fat Loss For the Win?
James Fries, author of the Stanford study, suggests that genetics and weight are the most prevelant risk factors when it comes to developing osteoarthritis. Overweight people are 4 times more likely to have joint issues than their lighter counterparts. Adds Fries:
A normally functioning joint can withstand and actually flourish under a lot of wear. Because cartilage -- the soft connective tissue that surrounds the bones in joints -- does not have arteries that deliver blood, it relies on the pumping action generated by movement to get its regular dose of oxygen and nutrients.
Run, But Run Sensibly
I still believe that caution must be taken when undergoing a running program. It should be added gradually, and should be an adjunct to lower impact cardio and strength training. Also, be sure to have appropriate footwear, train on softer surfaces, and pay attention to discomfort.