A quick Google search on “dehydration and running” brings up countless articles, but no consensus. Some advise drinking to thirst, while others say thirst is an unreliable indicator of dehydration. Some research suggests that even 2% dehydration reduces running performance, but other data isn’t nearly so clear. With so much contradictory information, what’s a runner to do?
Understand Dehydration
Dehydration occurs when you lose more body fluids (mostly water) than you take in. When you lose fluids through sweat, your blood volume decreases. This means your heart pumps less oxygen-rich blood to your muscles per beat, so running becomes harder and your pace slows.
On hot days, your body redirects blood flow to your skin to help cool you off, making even less blood available to your muscles. Running becomes increasingly difficult and your heart has to work harder to keep you moving. Worse yet, because your overall blood volume is already reduced, less blood is available to the skin for cooling. Your body then struggles to maintain its core temperature, which can lead to heat exhaustion.
Stay Hydrated
Experienced runners may want to read up on the full dehydration debate and tweak their hydration routine accordingly. But beginning runners can start by following some basic advice.
First, because you can lose 6-12 oz. of fluid for every 20 minutes you run, it’s important to pre-hydrate. Try to drink 8-16 oz. of water or sports drink one or two hours before your run. If that’s not possible, drink 4-8 oz. in the 15-30 minutes before your run. Then continue hydrating every 20-30 minutes during your run. Experiment with water, sports drinks, and electrolyte tablets to find what works best for you. Or, try one of these natural options.
In general, pale yellow urine indicates a healthy fluid intake level, while dark yellow urine and an elevated heart rate after your run indicate dehydration. You can also estimate your sweat rate to determine if you’re drinking enough fluids while you run.
Signs of dehydration include extreme thirst, dry mouth, weakness or fatigue, muscle cramps, and irritability. You can try drinking some fluids to alleviate mild symptoms. But if that doesn’t help, or if you feel any symptoms of heat exhaustion, stop running immediately.
Avoid Hyponatremia
As if that isn’t complicated enough, it’s also possible to drink too many fluids. This condition, called hyponatremia, depletes the concentration of sodium in the blood stream and can cause severe headaches, bloated hands and feet, nausea, and confusion. In extreme cases, it can be fatal.
Symptoms of hyponatremia can take several hours to appear, so pay attention to how you’re feeling a few hours after a long run or race. If you do exhibit symptoms, don’t drink large amounts of fluid until you’re urinating normally. And again, if symptoms persist, seek medical attention.
Dehydration and hyponatremia can be scary, but summer running doesn’t have to be. Just keep these tips in mind, listen to your body, and remember that your long-term health and safety are always more important than your immediate running goal.
By Meredith Lai
KCE Bonus: KCE volunteers stock water and Gatorade along our Saturday run routes. Look for the KCE-labelled boxes/jugs every 3 miles or so. On very hot days, you may also want to carry water.
This website contains general information about running, walking, and fitness, and should not be construed as medical advice. You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider.