It’s great to see more and more people running a marathon and finishing even though it may take some of them six or more hours to finish. Many people extol the virtues of finishing a marathon such as the ability to persevere, the sense of accomplishment , finding inner strength and so on. However, very little is said about the physical or health costs of running a marathon, especially when not fully prepared for it.
For example, because the immune system is severely taxed in running a marathon, many people become susceptible to colds and other illnesses in the days or weeks following the marathon. There are visible effects such as pain, soreness and extreme fatigue and many more subtle changes that take place that are not noticeable, but yet, that may be taking a heavy toll on the body.
For example, doctors have recently recommended that you should not get a physical examination soon after doing a marathon. The reason for this is that many of the negative changes in the body duplicate the symptoms of many other serious health problems.
This includes occult (not visible) blood in the stool which can also be a symptom of colon cancer, bleeding nipples, which is also a sign of breast cancer (even in men) and muscle injury that is part and parcel to the vigors of marathoning can indicate kidney and liver dysfunction. Creatine kinase levels can become elevated and erroneously suggest damage to heart muscle. Even abnormal red blood cell counts are sometimes found in people with mild dehydration.
Most of these changes seem to be temporary without long-term harmful effects to the body, but there have not been any multi-year studies to show the effects of such changes when experienced on a continual basis. In either case, it would be wise to be physically prepared to run the marathon before you tackle one.
This means developing sufficient aerobic endurance as well as muscular strength and endurance to enable you to run the marathon in a respectable amount of time without too many negative changes. Just doing some strength training for several weeks or a month is not sufficient. Most important is coupling the strength development with your running technique. This provides the greatest benefit.
With proper preparation you experience fewer negative effects. This in turn, allows you to do marathons without any problems and ill effects as a very noticeable outcome.
For more information on this and related aspects of running see Explosive Running and Build a Better Athlete