Do Marathons Really Cause Kidney Damage?
The popularity of marathon running has grown significantly over the years. Currently more than half a million people participate in marathons each year. It is known to be one of the biggest accomplishments in a runner’s life given the grueling training involved in the preparation. There is no doubt this difficult training has an affect on different parts of the body, especially for individuals who already have a history of pre-existing conditions or disease. The heart has been studied a great deal over the years as it is the organ with the biggest role in the training and racing of a marathon. It is in charge of controlling the blood flow to and from different parts of the body, most importantly to the working skeletal muscles. Supplying the majority of the blood to the muscles and skin during running must mean there is less blood flow to the other organs.
Acute Kidney Injury
One organ that has been less frequently studied in the case of marathoners and other endurance sports is the kidneys. One would think the effects of long distance running on the kidneys would be one of the most important factors considering the high incidences of dehydration and heat stroke in sports, yet not much is known yet about the relationship between kidney disease and endurance training. A recent study evaluated the serum creatinine levels in urine samples of 22 runners before and after running a marathon and concluded that 82% of them resulted to have acute kidney injury (AKI) following the race. AKI is when there is a build-up of waste products in the blood that the kidneys are currently too weak and damaged to filter out. During this short-lived injury, the kidneys have a hard time maintaining the proper balance of fluids in the body. This condition was found in the runners shortly after the conclusion of the race and the serum creatinine levels went back to normal levels by the second day following the race.
Although this study proved that there is some kind of temporary kidney damage that occurs during running a marathon, it questions whether these effects lead to chronic kidney disease (CKD) over time. There is a large percentage of marathoners who train year round for this sport almost their entire life, so it would make sense to evaluate the effect of this type of endurance training on the kidneys. The main limitation of this study was the small sample size of 22 runners, but since it yielded a high percentage of AKI development, it is sufficient enough to encourage further studies of both AKI and CKD in relation to marathons. The other few studies regarding kidney damage in distance runners showed that the majority of cases that developed AKI following a marathon were either taking non-steroidal anti-inflammatory drugs or other medications, had a bacterial or viral infection present in the body, or other medical condition that had a negative affect on the kidneys at the time.
High Risk Factors
External and environmental factors have been shown to be associated with a higher risk of developing acute kidney injury during a marathon. As mentioned above, the majority of cases with positive results in the studies had at least one other factor present such another disease or infection, the use NSAIDs or other analgesics, or were found to be in an extreme dehydrated state. The information regarding these associated factors that lead to a higher risk of kidney damage is enough to encourage altering training plans and habits to avoid these factors as much as possible.
Rhabdomyolysis is a condition where skeletal muscle becomes severely damaged and its contents leak into the bloodstream. This eventually leads to kidney damage where the kidneys are unable to filter out these waste products. This condition has many causes including direct crush injuries such as in an automobile accident, prolonged muscle strain especially in untrained athletes who perform high impact resistance exercise, prolonged hyperthermia, and the use of certain medications, among many others. Rhabdomyolysis is more dangerous in individuals who have more muscle mass, such as in a bodybuilder. If treated promptly, the acute kidney damage is reversible.
The use of certain analgesics, such as non-steroidal anti-inflammatory drugs, increases the risk of developing acute kidney injury in marathon runners, as well. These medications decrease the blood flow to the kidneys in general, which ends up exacerbating the kidney damage since blood flow is already reduced during prolonged running due to the increase in blood flow to the working muscles and skin. This may be a concern for runners if they have a habit of taking medication before a race to limit pain of any kind.
Heat Illness and Dehydration
There is a large amount of research that has determined the detrimental affects of dehydration in runners and other endurance athletes. Participating in races where the temperatures are high and the weather is humid will increase the risk of becoming dehydrated. Dehydration is directly linked to kidney function since the kidneys are in charge of regulating the body’s fluids and electrolytes. Exercising for prolonged periods in the heat will create a large spike in core body temperature, which means blood flow will concentrate itself to the skin in an attempt to lower the temperature. This process will eventually lead to the lowering of blood pressure and decreased blood flow to the kidneys, since the kidneys are not the primary concern of the blood flow in this state.
Given the information gathered from the few studies on acute kidney injury in marathoners, it is enough to aid in altering our training programs and some daily habits to lower the risk of developing any issues with the kidneys at all. If it is a condition that is inevitable in marathon runners, then what is concluded so far is that the AKI is reversible within a day or two of racing. As far as what we can do as runners to help avoid this kidney damage, there are some measures that are simple to follow.
Maintaining our bodies in a good hydration state is a controllable factor. Easy rules to apply are to drink enough water throughout the day, arrive hydrated to races, and keep up with the proper electrolyte balance our kidneys require to limit dehydration during the race. It is also important to limit the use of pain medication as much as possible and adopt other pain management strategies. Proper training to help avoid medical problems such as rhabdomyolysis include ensuring gradual increases in mileage and resistance during strength training monitoring any symptoms of overtraining. As with any other medical condition, seek advice from a professional if you are experiencing any symptoms that arise during or after running. It is best to have a proper physical examination by a doctor to be aware of any pre-existing conditions that increase the risk of developing kidney dysfunction.