However, read these same magazines and websites in June, and then they're discussing the dangers of drinking too much (scientifically called hyponatremia) and how over-hydrating can be deadly. What once seemed a pretty simple strategy to beat the heat gets a lot more confusing.
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Luckily, with a little planning, a helpful calculator—and a better understanding of hydration in general—you can easily calculate exactly how much fluid you need for optimal performance in any temperature -without being in danger of over-hydrating.
What is Hyponatremia?
Simply stated, hyponatremia is caused by a disturbance in the balance of electrolytes in your body, more specifically sodium, which is typically the result of drinking too much water.
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When the sodium level in the body's cells gets too low, water moves into the cell in an attempt to balance fluid levels. This causes the cells to swell, which isn't a problem for most cells in your body—except for those in the brain.
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Brain cells can't expand when the cells swell because of how tightly they are confined within the skull. Consequently, the brain begins to swell itself, which induces symptoms such as headache, nausea, cramps, confusion, and fatigue. In addition to being dangerous, these symptoms are also common signs of dehydration, which make diagnosing the problem difficult.
To prevent hyponatremia, it's important that runners drink only enough water to replace what they've sweated out and balance this water intake with electrolytes to maintain metabolic stability.
More: Running and Breathing 101
Why Sports Drinks May Not Be Your Friend
Electrolytes are electrically-charged ions your cells use to carry electrical impulses (such as the nerve impulses and muscle contractions critical to running) across themselves and to other cells. Electrolytes are necessary for your digestive, cardiac, muscular, and nervous systems to function well.
Electrolytes are commonly found in sports drinks, such as Gatorade? and PowerAde?. However, what many runners don't realize is that the speed of absorption of fluids into the body is largely dependent upon the composition of the fluid in terms of its carbohydrate (sugar), sodium (salt), and potassium concentrations.
As a general rule, the higher the carbohydrate content, the slower the absorption rate. Therefore, trying to maintain proper hydration and balanced electrolyte levels with sugary sports drinks is difficult. Because of the high sugar content of most sports drinks, the fluid is not readily absorbed into the blood stream.
Furthermore, the body monitors electrolyte losses during running through hormones. After a run, if electrolytes are consumed in high amounts, it neutralizes the hormonal system and disrupts the body's regulation processes. Therefore, chugging down a sports drink or electrolyte tablet after a run isn't going to lead to optimal performance during the next run and increases health risks related to electrolyte imbalances after.