As we showed in our last post, overhydration can actually have a negative impact on athletes. Researchers at the British Medical Journal found that exercise induced dehydration of up to 2.3% of body weight significantly improved performance. In addition, overhydration may actually be more dangerous than dehydration.
The general theory behind fluid consumption is to prevent dehydration. It is widely believed that dehydration can lead to severe health problems, including muscle cramps and heat illness. However, the science does not support these theories. According to Dr. Kevin Miller, an associate professor of athletic training at Central Michigan University, “based on current evidence, it does not appear that dehydration directly contributes [to those problems].”
Professor Tim Noakes agrees, stating, “Dehydration is not a disease, and it only has one symptom, and that is thirst.” Indeed, studies have found that being dehydrated, even up to 3% of an athlete’s body weight, does not increase the likelihood to suffer from heat-related problems.
Overhydration, on the other hand, is scientifically proven to have serious, even life-threatening side effects. In an attempt to absorb extra fluids, your cells begin to swell, leading to stomach upset, dizziness, and soreness. As more fluids are consumed, the swelling worsens, which becomes increasingly problematic for your brain. Dr. Noakes writes,
“The brain swells, and because it is in a rigid skull, it cannot swell very much. The more it swells, the more pressure, and that eventually squeezes the arteries supplying blood to the brain. Ultimately, there is less oxygen getting to the brain, and certain parts become damaged. Once it affects your breathing centers, then you’re in real trouble, because it stops breathing, and that is essentially irreversible.”
In addition, overhydration is actually shown to make athletes more susceptible to muscle cramps than dehydration. In 2004, Dr. Martin Schwellnus, a professor at the University of Cape Town, performed a study on runners participating in the Two Oceans marathon. The racers were matched by body mass and finishing times, and several variables were tested. One key finding was that the athletes who cramped had lower sodium levels than the athletes who did not cramp. This means that the crampers were actually more hydrated than the non-crampers.
Ultimately, it’s not that drinking fluids is dangerous; it’s that over-drinking fluids is. Professor Noakes argues that we, as a society, have become too fearful of dehydration, and too programmed to overdrink. Water is important, but only at the appropriate levels. Athletes do not need to be told when to drink - our bodies have evolved to do just that. As long as we listen, it is nearly impossible to become dehydrated. As Noakes puts it:
“If you start to exercise, and you don’t drink, after a period of time, you will become thirsty—that’s your body’s way of telling you to drink.
The idea that you should drink ahead of thirst is absolutely nonsensical... why should humans be different from every other creature on earth to be told when and how to drink? The reality is you don’t need to be told when and how much to drink.
We have a 300 million year developed system that tells you with exquisite accuracy how much you need to drink and when you need to drink. It’s called thirst. If you rely on thirst you won’t ever become dehydrated, and you won’t also ever become overhydrated.”