Dear Dr. Toshi,
"My doctor told me to stay hydrated. Should I drink water? How much should I drink?"
I used to help out at marathons as a staff member in a medical tent. As you may know if you participated in an event like that or saw a marathon on TV, there are hydration stations along the route, where athletes can get fluid along the way. There are usually water stations and sports drink stations, like Gatorade stations. (In Milwaukee, I once helped at a marathon called Oktoberfest Milwaukee Marathon, and there were actually beer stations, too, though I don't recommend drinking beer while participating in a marathon!)
People who didn't drink anything along the way tended to collapse due to dehydration and heat, and they often ended up in the hospital. There were also people who collapsed because they only drank water after sweating a lot in the heat. That's because they didn't replenish their electrolytes (mainly sodium in this case) or get any sugar for energy. People sweat out salt (sodium), and when they drink a lot of water during very strenuous exercise, the salt in their bodies gets too diluted, which makes them very sick. Dilution of your electrolytes can even be fatal. (The main electrolytes in the body are sodium, potassium, chloride, magnesium, calcium, phosphorus and bicarbonate, but the main one in sweating is sodium.)
About sixty percent of your body is water. That's more than half of your body. And muscle is about 80% water. So, water is essential for your wellbeing. Water plays many roles in your body, like keeping your body temperature normal; lubricating and cushioning joints; protecting your internal organs and tissues; getting rid of waste products through urination, bowel movements, and perspiration; maintaining the right balance of electrolytes, carrying nutrients and oxygen to all the cells in your body; helping digestion; preventing constipation; maintaining good blood pressure; stabilizing your heart rate, helping your metabolism, and many other things.
When you don't drink enough water, you get dehydrated. Dehydration not only affects all the things I just mentioned above, but also your muscles, energy level, and even your brain function! There have been studies showing that a loss of only 1-3% of your body weight in water can impair your brain function, and one study showed that loss of just 1.6% of water from your body decreases your working memory! Dehydration can also negatively affect your mood and concentration.
One of the most common symptoms of dehydration is a headache. Low water consumption is also associated with constipation. And it can make your urine look dark yellow or orangish. If you're well hydrated, your urine should be pale yellow or almost clear.
We all wonder about how much water we should drink every day. Actually, there is no set amount because it depends on your overall health and conditions, exercise level, and environment. If you have medical conditions that affect your thyroid gland, heart, or kidneys, for instance, the amount you should drink may be different from other people who don't have those conditions. So, please ask your doctor.
The National Academies of Sciences, Engineering, and Medicine determined that adequate daily fluid intake (which includes water, food, other beverages) for a healthy person is about 15.5 cups (3.7 liters) for men and 11.5 cups (2.7 liters) for women. According to Mayo Clinic, about 20 % of our fluid intake comes from food. That means fluid from sources other than food should be about 12.4 cups for men and 9.2 cups for women. Does that sound like a lot to you?
Many medical experts recommend drinking eight 8-ounce glasses of water (2 quarts, or half a gallon) of fluids per day. If you sweat heavily, you may need to drink 2-3 cups per hour. But you have to remember that if you exercise intensely for more than an hour, you should start drinking some sports drinks to replenish your electrolytes that you lose from sweating and sugar that you need for energy.
It's uncommon, but you can actually overdose on water! I've seen people become very sick after drinking too much water and no sports drinks in long, intense exercise like marathons, and also people who were sick with diarrhea and decided to hydrate themselves with just water. To prevent this, they could drink a sports drink along with water since sports drinks contain electrolytes. Some examples of drinks that contain electrolytes are Gatorade and Powerade, but they contain a lot of sugar. Pedialyte is one with less sugar. If have more questions, please ask your doctor.
Dr. Toshiko (Toshi) Luckow, MD is a Family Medicine physician at the West River Health Services hospital and clinics.