Half of children may not be drinking enough water

June 30, 2015  |  General

Adequate hydration, getting enough water, is vital to good health. After all, we’re mostly made of water — about 60% of our bodies is water. Our bodies are quite good at hanging on to most of this water. Our skin holds nearly all of it inside, for example. But we do lose water through what we call obligatory or insensible losses. Some is lost through our skin, such as through sweating. A fair amount is lost through our breath, since the air we breathe out is fully humidified. Our kidneys also lose water through urine. Even though these organs are very, very good at conserving water, they still need to manufacture a minimal amount of urine to keep good function. So we need to take in water every day. There is some water in food, of course, more in some foods than in others. But the bulk of our daily water needs come from drinking.

How much water do we need every day? A good general rule is that an average adult male needs around 3 liters (about 3 quarts) per day and an average adult woman requires 2.2 liters. Of course that is just the baseline. If you are doing something that increases water loss, such as moderate or severe exercise, you need additional water on top of the basal amount to make up for what you are losing. What about children? On a per weight basis children generally need more. We have some simple calculations we use to determine what we call their maintenance fluid need: 100 mL/kg for the first 10 kg of body weight, 50 mL/kg for the next 10 kg body weight, and 20 mL/kg for every kg after that until the child is adult sized. That works out to about 1 liter/day for a 10 kg (22 pound) child, 1.5 liters/day for a 20 kg (44 pound) child, and 1.9 liters for a 40 kg (88 pound) child. Again, that’s just the baseline; you need to add more for activity.

Our thirst mechanism is a key way we regulate our water, but both adults and children can take in less than their requirement but not get too thirsty if the deficit is not much. Yet that water deficit can still be significant. Chronic, mild dehydration makes you feel generally unwell, something probably all of us have experienced. For example, if you’ve been out and about most of the day and feel a bit lethargic — maybe you have a mild headache as well. Then you drink a tall glass of water and within a few minutes feel much better.

An interesting recent research study asked the question if children are, on average, as hydrated as we would recommend. They used data from the National Health and Nutrition Examination Survey, which spanned the years 2009-2012, and involved over 4,000 children between the ages of 6 – 19 years. The study was a powerful one because it didn’t just ask parents how much fluid their children drank; it measured the osmolality of the urine, which indicates how concentrated the urine is. The body normally makes urine more concentrated if it is trying to conserve water because the person isn’t drinking much.

The results were interesting. The authors found that just over half of all children were not optimally hydrated. They weren’t dehydrated, that is to say sick, but their urine osmolality was higher than what we would recommend. The authors also calculated that around 8 ounces of additional water (about 350 mL) would be sufficient to bring the average school age child up to the recommended amount. That’s the size of a standard kitchen glass of water.

The take home message for me is to offer your children plenty of water at meals and make sure they take water with them when they go to various activities, especially sports.

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