No, kids are not dehydrated, and their water intake isn’t a crisis.

Austin trolled me with this story yesterday. He’s the best at it. The rest of you are just poor imitations:

Most American children and teenagers aren’t drinking enough fluids, and that’s leaving them mildly dehydrated, according to a new study. In fact, one-quarter of a broad cross-section of children ages 6 to 19 apparently don’t drink any water as part of their fluid intake.

The Harvard scientists who turned up the finding were initially looking into the consumption of sugary drinks in schools and looking for ways to steer children toward water instead — a much healthier beverage.

Here’s the study. “Prevalence of Inadequate Hydration Among US Children and Disparities by Gender and Race/Ethnicity: National Health and Nutrition Examination Survey, 2009–2012“:

Objectives. We evaluated the hydration status of US children and adolescents.

Methods. The sample included 4134 participants aged 6 to 19 years in the National Health and Nutrition Examination Survey from 2009 to 2012. We calculated mean urine osmolality and the proportion with inadequate hydration (urine osmolality > 800 mOsm/kg). We calculated multivariable regression models to estimate the associations between demographic factors, beverage intake, and hydration status.

And here’s what they found. More than half of the kids had a urine osmolality greater than 800 mOsm/kg. They also found that drinking 8 oz more of water was associated with a statistically significant chance of having your urine osmolality be  less than 800 mOsm/kg. For the record, that extra water was associated with decrease of urine osmolality of 8 mOsm/kg (which is really tiny), and sugar-sweetened beverages were associated with a decrease of 10 mOsm/kg (which is still tiny, but larger), so these are really more statistically significant results than clinically significant results. Also, MILK MADE NO DIFFERENCE.

But the take home message for the media is less about the water and more about the panic that kids are dehydrated. More than half of them! But are they?

Here’s the thing: urine osmolality is not a very good test for this. There’s no “normal” range as far as I know, as the values you’d see would be all over the map. Most sources I see call a spot urine osmolality test (which this was) of up to 1200 mOsm/kg still in the physiologic range, and up to 900 in the typical range. Kids also vary more than adults. Sources for this: here and here and here and here and here (I’m stopping now). You will have a hard time finding a source that says “be concerned above 800 mOsm/kg”. But that’s how this study defined it.

In fact, that’s how all the studies that panic about kids being dehydrated define it. Here’s a study that says that about two-thirds of kids in LA and NYC are dehydrated and not drinking enough water. Here’s a study that says about half of French children are. Here’s a study that “predicted” that boys would have an average osmolality of 598 mOsm/kg, but found that the median osmolality was 844 mOsm/kg.

At some point, maybe we should all admit that the values we’re calling “dehydration” aren’t dehydration at all. When more than half of all kids, all over the world, are defined as “sick” by your laboratory measure, and kids appear to be doing better than at any other time in the history of the world, then it’s likely your laboratory measure needs some rethinking.


P.S. Also, pure water isn’t magic, and you don’t need eight glasses of it a day. You get hydrated from lots of things. I was writing about this even in the long ago, in the BMJ.

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