Dr. Mitch Shulman: Facts about summer hydration

How much should you drink, what should you drink, and at what temperature?

There’s a lot of confusion as to how you should keep yourself properly hydrated as the summer heat and humidity attack. Our body consists of cells and tissues that are filled with liquid. We have to keep enough inside to meet all the various needs of circulation, metabolism, cooling and waste management. Our brain triggers thirst when it senses we’ve fallen a certain per centage point below optimum, but you don’t want to wait until then to replenish your liquids because performance is already slightly reduced.

So, how much should you drink? What should you drink? And, at what temperature?

First question: how much? Typical medical answer: it depends. Sorry not to give you a hard and fast rule but the truth is it’s a function of what you eat, how active you are and the temperature. How then to know how much to drink? You should be going to the bathroom regularly throughout the day. When you void, your urine should be almost transparent, maybe faintly yellow — except first thing when you wake up because you’ve been fasting while you were asleep and so your urine will be dark and concentrated. If it’s not almost clear during the rest of the day, you need more liquid.

What should you drink? Anything. I usually tell folks that a mix of different sources is best. Too much water only, won’t replace the natural salts and minerals that are lost in trace amounts in your sweat. I am also afraid of the high sugar content of many drinks, so I warn people to read the labels and consider diluting many electrolyte drinks and juices half and half with water. Also, many fruits and vegetables — tomatoes, cucumbers, watermelon, cherries, grapes — have a high liquid content and will supply some of your needs.

At what temperature? Here at home, when heat and humidity are both elevated, cool drinks are probably best. Often, you’ll hear that people recommend hot drinks based on the experience in certain other countries. That’s because the heat is a dry heat with low relative humidity in many of these places. Under those conditions if you drink a hot drink or eat spicy foods you will sweat more. As a result of the low humidity your sweat will function as it’s supposed to as a very effective way to lose extra heat by evaporation. However, when the humidity is high, evaporation slows down dramatically, which is why you see people covered in sweat. It can’t evaporate fast enough and that’s why when the humidity is elevated our best way of losing heat (the evaporation of sweat) is much less effective. That’s one reason why we are at a much high risk of heat stroke and heat exhaustion when both the heat and the humidity are high.

So now you know. Please be careful and respect the high heat and humidity. Even Olympic athletes give themselves weeks to acclimatize before they compete. Don’t treat yourself any differently.

Dr. Mitch Shulman is an Assistant Professor, Dept. of Surgery, McGill Medical School and an Attending Physician, Emergency Department, McGill University Health Centre. He’s also the CJAD AM 800 Medical Consultant.

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