When I wrote about exercising in the heat yesterday, I touched briefly on the issue of hydration. The June Nutrition Action Health Letter, published by the Center for Science in the Public Interest, offers much more information on how much—and what kind of—water to drink. One article is a Q&A with an expert on kidney function, discussing what science says about how much water people really need to drink. The other analyzes the ingredients in so-called water beverages like VitaminWater, Propel, and SoBe Life Water and concludes you are probably wasting money and calories if you're expecting these drinks to provide any health benefits.
The CSPI hasn't yet put up the latest issue online; check back in a week or so to see if it provides direct links to the two water articles. (The newsletter itself costs $10 a year.) In the meantime, here's a quick rundown on the water stories.
The interview with Heinz Valtin, a physician and professor emeritus and former chair of the Department of Physiology at Dartmouth Medical School, shoots down the idea that healthy people who aren't exercising heavily, working outside, or living in hot climates need to drink eight glasses of water a day. (As I noted yesterday, people who do exercise heavily out in the heat need to follow their thirst.) The notion that coffee, tea, and soft drinks dehydrate you is also a myth; in the amounts found in those beverages, caffeine isn't a diuretic. Valtin also says that there's no strong scientific evidence that drinking water helps you lose weight or that it helps prevent constipation, though if you feel better when you stay hydrated, that's fine. Also not true: If your urine is dark yellow, you're dangerously dehydrated. The bottom line for everyone is to drink when you're thirsty.
Consumers are snapping up enhanced waters, the second article says, despite the fact that the health claims they're making are shaky at best. The piece points out, for example, that there's no evidence that the vitamins in VitaminWater's B-Relaxed Jackfruit-Guava (B plus theanine) will do anything to calm you down, as the label claims. The fiber in Aquafina Alive Satisfy is not the same as the fiber found in veggies and grains (this isn't spelled out on the label), and it's not clear whether it will bring the same benefits. Moreover, the piece says, these drinks may have more calories, artificial sweeteners, and caffeine than people think.