marathon runners

With the New York City Marathon quickly approaching on Nov. 5, we've been wondering about these grueling races, in general. How many people run one each year? What's the average finish time, or the average runner's age? The answers, culled from last year's race data, may surprise you.  
A new study in the American Journal of Kidney Disease shows that acute damage to the organ can occur in marathon runners, of which there are more than 500,000 in the United States. But how significant is this work? Let's take a look.