Overhydration: Is the Fear of Dehydration Causing you to Drink Too Much?
Last week we talked about sports drinks, their role in performance, and suggested guidelines for intake. Despite what I know about sports drinks and hydration, I rarely drink during training or racing. If time and location permits, I might steal a drink or two from the bubbler (a.k.a. water fountain to those who are not from Milwaukee), but I have never been able to do much with fluids during exercise other than throw them on my head.
I recall trying to drink water from a cup once, about 5 miles into the US ½ Marathon Championships and ended up choking on a small sip and getting the remainder of the water up my nose. I decided not to try again for the rest of the race. I finished 6th and set a 5+ minute PR.
An Insight On Dehydration
There was no question that I was dehydrated after the race, but could I have performed better if I had ingested more fluid? Or even more interesting of a question, could I have performed worse? Can drinking according to the recommendations of leading sports medicine organizations cause more harm than good?
That is the question addressed by Dr. Tim Noakes in his recently published book Waterlogged: The Serious Problem of Overhydration in Endurance Sports. (Affiliate link) In his book, he challenges the research and findings that have been used to develop fluid recommendations for athletes. Most notably, he points to significant findings from this research that show no ill effects or impaired performance in athletes who drank little to nothing. He argues that dehydration is simply a reduction in total body water content and the only symptom is thirst.
Dehydration has mistakenly been to blame for heat-related illness in endurance exercise but the fact is, the top elite finishers are often the most dehydrated of all runners.
Overhydration, on the other hand, is a more serious condition with life-threatening complications and it can result from an athlete simply trying too hard to prevent dehydration.
Overhydration and Hyponatremia
Hyponatremia (low blood sodium levels) is one of the most common medical complications in long-distance training and racing and is the cause of a large number of race-related fatalities.
Athletes at greatest risk are novice runners or slower runners who may take 4-5 hours or more to finish a marathon and who are drinking mainly water. These runners often have an easier time drinking while running at a slower pace and also have more time and opportunities to fill up on fluids.
As the marathon and other long-distance races become more popular, especially among newer recreational runners, more athletes are likely to be at risk for hyponatremia.
The exact mechanism behind hyponatremia is not clear, but it is known to be associated with the over-consumption of hypotonic fluids (like water). It is important to note that hyponatremia can develop from drinking too much fluid before, during, and even after the race. Furthermore, hyponatremia can also develop from over-drinking sports drinks, despite the fact that most contain sodium.
Signs and Symptoms of hyponatremia
Although the signs and symptoms of hyponatremia have been described as similar to those of dehydration. Noakes points out that the only true symptom of dehydration is thirst. Symptoms associated with hyponatremia include:
- Muscle weakness
- Nausea and vomiting
If left untreated or misdiagnosed as dehydration, hyponatremia can progress to seizure, brain swelling, pulmonary edema (fluid buildup in the air sacs of the lungs), comatose, cardiorespiratory arrest, or death.
How Much Water Is Too Much?
For many years now, the American College of Sports Medicine (ACSM) has recommended that athletes drink four to eight ounces of fluid every 15 to 20 minutes of running. Furthermore, they warn that greater than a 2% reduction in body weight due to dehydration will impair performance.
These recommendations were based on early studies (Wyndham and Strydom) suggesting that the level of dehydration determines the body temperature response to exercise and thus, the development of heat-related illnesses. Heat-related illnesses would not only be detrimental to performance, but could also be dangerous and potential fatal. Thus, guidelines for hydration during exercise stressed the importance of drinking as much as possible, whenever possible, to prevent any instance of dehydration.
Results and Recommendations
In his book, Noakes addresses several issues with these recommendations and the studies on which they are based, and explains why they are not really applicable for the majority of runners.
- The findings from the studies on which these recommendations were made involved “better-than-average” male athletes. Fitter athletes are more trained to be able to sustain the body temperature stresses of intense running, they tend to have higher sweat rates and greater sodium losses than less fit runners, and also men generally have higher sweat rates than women.
- Noakes feels that these studies fail to recognize the body’s biological controls that have evolved over time and allow the body to survive and persevere when under environmental stress.
- The maximum rate at which the intestines can absorb fluid is, on average, about 600 mL (or 20.3 fl oz.) per hour. The kidneys can only excrete fluid at a rate of about 800 mL/hr in males and closer to 600 mL/hr for smaller females. If fluid is ingested above these rates, it will be retained and may cause a number of problems associated with hyponatremia.
- Subjects participating in these studies had a difficult time drinking at the high rates that are required to prevent weight loss when running at such a high speed and intensity.
- Dehydration, or rather a reduction in body weight due to exercise, is a normal part of exercise. The only symptom of dehydration is thirst and often, this thirst becomes overwhelming that the athlete is compelled to drink when fluid is available. Furthermore, studies have disproved the claim that a reduction in body weight <2% results in impaired performance.
- There is a lack of evidence to support the theory that not drinking during exercise is dangerous.
A recent meta-analysis of laboratory-based studies examining the impact of dehydration on performance (Goulet) resulted in the following conclusions.
First, it was found that a reduction of body weight of 2.2% was not associated with a decrease in performance.
Second, it isn’t dehydration itself that is responsible for any decrease in performance, but rather not drinking in response to thirst.
Drinking enough to satisfy thirst resulted in a 90% performance advantage compared to drinking below thirst and a 63% performance advantage over drinking above the thirst response.
The results of this meta-analysis show, for the first time, that drinking according to thirst is the superior hydration protocol to maximize performance.
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- Learn how in-tune you are to your thirst mechanism. Intense focus on exercise and race can mask the thirst sensation so pay special attention to your need for fluid during training. Furthermore, be aware of the signs and symptoms of dehydration and hyponatremia.
- Many races feature a particular sports drink or beverages and marathoners often receive the message that they need to drink a lot and drink often to prevent dehydration. While you don’t need to, and shouldn’t, skip the aid stations completely, it is important to go in with a plan. If you find you are gaining weight during your runs, then you are drinking too much and should appropriately reduce your fluid intake. If you are losing weight but not feeling thirsty, it means you don’t need to worry much as long as you start adequately hydrated and replace fluids upon completion.
- Lastly, keep in mind that sports drinks are often the easiest way to get carbohydrate during exercise. Even if you use gels or blocks, you need some fluid so that sugar can penetrate your blood quickly. So if you are using a carbohydrate source during your race, don’t forget to factor those fluids into your plan.
There are clearly opposing views on proper hydration protocols for endurance exercise. Hopefully, this article brought to light the real danger of over-consuming fluids while participating in long races, but I am sure it has also left many confused on what to do about hydration. The take-away message is that it is important for each athlete to know their individual sweat rate and have an individualized hydration plan for a variety of races and seasons.
1. Noakes, T. Waterlogged: The Serious Problem of Overhydration in Endurance Sport. Champaign, IL: Human Kinetics; 2012.
2. Rosner, MH, Kirven J. Exercise-associated hyponatremia. Clinical Jounal of the American Society of Nephrology, 2007;2(151-161).
3. Goulet, ED. Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British Journal of Sports Medicine, 2012.
4. Wyndham CH, Strydom NB. The danger of an inadequate water intake during marathon running. South African Journal of Medicine, 1969; 43(893-896).