Ask the Doctors

Dear Doctor: How does someone know they're dehydrated? I'm worried because my husband swears he drinks "tons" of water, but as best I can tell, he doesn't have more than a glass or so per day, even when it's really hot. He's very active and he's always got headaches, which he blames on air quality, and he's often tired. How can I persuade him to drink more water?

Dear Reader: Hydration can be a tricky thing. Unlike hunger, which triggers physical signals that are pretty robust, the signs of thirst can be more subtle and easier to ignore. However, drinking enough water is crucial to both physical and mental well-being. The adult human body is made up of 60 percent water. It's the main component of our cells and tissues; it's the environment that makes the various transport systems within our bodies possible, and it plays an essential role in the various chemical and electrical processes that keep us alive and healthy. That means we have to continuously replace the water we lose each day through sweat, urination, breath and in various other physiological processes.

We replenish the water our bodies use through the foods we eat and the fluids we drink. According to the National Academy of Sciences, total water consumption for women should be 91 ounces daily, and for men the number is 125 ounces. Depending on your diet, up to 20 percent of that water will come from foods like fruits, vegetables and liquid dairy products like milk, kefir and yogurt. The balance of the deficit has to be made up through beverages. When it comes to hydration, not all beverages are created equal. Although sodas and fruit juices do provide water, they also deliver a hefty dose of sugar. Coffee, tea and other caffeinated beverages can have a mild diuretic effect. And sports beverages, while marketed to replenish the sodium, potassium and magnesium we lose through sweat, are pretty high in sugar as well.

We can't know for sure the cause of your husband's headaches and fatigue. However, both of those, along with dizziness, loss of appetite, constipation, heat intolerance and blood pressure fluctuations are symptoms of dehydration.

Studies show that we also pay a cognitive price for dehydration. Researchers at the Georgia Institute of Technology found that losing as little as 2 percent of your body weight in fluids -- that's 2 pounds per every 100 pounds that you weigh -- led to impaired decision-making and a lack of mental focus. Not only did motor coordination take a hit when study participants became even mildly dehydrated, they also began to flub mental tasks like reading maps, doing arithmetic in their heads and proofreading. The more dehydrated participants became, the more their performance deteriorated.

In your husband's defense, dehydration can be difficult to discern. It's a somewhat crude measurement, but keeping an eye on urine color can help him to track what's going on. A very dark gold equals dehydration. We hope that learning about the physical and mental toll of skimping on water will persuade your husband to take hydration more seriously.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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