For those wondering, this blog covers two main things — stuff important to instructional design, and stuff important to my statistical literacy class. Here’s something on the latter…

Somewhere, somebody, probably employed by a bottled water company, said we should all get eight glasses of water eight times a day. Coffee doesn’t count, the water in your Hamburger Helper doesn’t count. Beer doesn’t count. It must be water, or something close to it.

That’s not remarkable, that sort of thing happens all the time. 

What’s extraordinary to me is how resilient the myth has been in the face of overwhelming scientific evidence it is nonsense. The BMJ just published an article on this, but back in 2002 an article in the American Journal of Physiology completely debunked it. Snopes looked into the history of the claim in 2005 and found some of the water-as-cure-all garbage came from the self-published 1995 junk science book Your Body’s Many Cries for Water, subtitled “You are not sick, you are thirsty!”

Since 2002 I have seen this claim repeatedly debunked or at least set aside as a not-so-helpful formulation. There is disagreement, but where you look at actual experiments (see here for a summary up to 2002) it’s pretty clear that:

• People without special circumstances (such as working hot days, taking certain medications, etc) can just drink when they are thirsty and they’ll be fine.
• The amount people need is highly variable anyway.
• Caffeinated and alcoholic beverages consumed in moderation count towards your fluid intake, not against it.
• Did I mention you can just drink when thirsty and you’ll be fine?

Basically the normal person needs to worry as much they are getting enough fluids as they have to worry they are getting enough calories.

So why does the myth stick around? I mean, if we can’t get people to understand that sticking 2 liters of water down your throat no matter what your activity level or food intake is not now, and never has been a requirement for health, what chance do we have with the Global Warming debate, where there are real stakes? 

I don’t really have an answer for that, except to hope that we can get people in the habit of interrogating research without becoming cynical (It’s not all opinion, right? Here’s a case where science just tells us the 8 glasses people are wrong). The fact that the “8 glasses 8 times” was so sticky in our public consciousness shows that we crave quantitative formulations. We just have to be more discriminating about which ones we embrace…