The importance of staying well-hydrated during exercise can’t be underestimated. When you work out, especially in a warm environment, you lose significant amounts of water and electrolytes through sweating. This loss of fluid not only decreases exercise performance, it can lead to serious dehydration or even death. That’s why you see so many runners chugging on a bottle of water as they pound the pavement. Most people assume the more water they drink the better. Not necessarily so. Drinking too much water during exercise can lead to a life-threatening condition called hyponatremia.
What is Hyponatremia and How Does It Affect People Who Exercise?
Hyponatremia simply means low sodium levels. When a person runs or exercises for a long period of time, they lose water along with electrolytes like sodium through their sweat. If they drink water, they replace some of their water loss, but they don’t replenish the lost sodium. It usually takes a prolonged period of exercise of one to three hours to experience a significant drop in sodium. But if a runner drinks pure water without sodium, it dilutes out the already declining level of sodium in the bloodstream. This can lead to dangerously low sodium levels.
According to one study of runners in the Boston Marathon, 13% had hyponatremia during the race. The risk was higher in those that drank larger amounts of water during the race and took the longest time to finish. By taking a longer time to reach the finish line, they had time to lose more sodium and drink more water to make the situation worse.
What kind of problems can hyponatremia cause? When sodium levels fall too much, cells in the brain begin to swell. This leads to symptoms like headache, confusion, muscle weakness, vomiting, seizures, hallucinations, and, in severe cases, coma and death. More than one marathon runner has not made it to the finish line because of low sodium levels from drinking too much water.
How Can You Prevent Hyponatremia From Exercise?
The key is to drink enough water to replace the amount you lose through sweat without overhydrating. If you’re taking place in an event such as a marathon, estimate your fluid needs beforehand. The best way to do this is to measure your weight before and after exercise. If you lose more than 2% of your body weight, you’re not drinking enough, but if you gain weight, you’re drinking too much.
Another option is to replace fluids with a sports drink that contains adequate amounts of sodium and electrolytes to make up for some of the sodium lost through sweat. If you’re exercising in a warm environment for more than an hour, a sports drink is a safer alternative for hydration. Look for one that’s not sweetened with fructose since some people experience bloating, diarrhea and cramps from fructose-sweetened drinks.
The Bottom Line?
Hydration is important but so is sodium balance. Hyponatremia is a life-threatening condition that’s most likely to occur during long periods of exercise where fluids are replaced with water instead of an electrolyte-rich drink like a sports beverage. Get an idea of your fluid needs, and drink only enough to replace what you’re losing through exercise. If you’re working out for more than an hour, use a sports beverage for fluid replacement instead of water.
American College of Sports Medicine Reports. “Strategies to Prevent Hyponatremia During Prolonged Exercise”