Monday, August 6, 2012

Hydration education

As I've mentioned before, it's hot here in Skepticville and with extreme heat comes a risk of dehydration.  SkepticRD happens to work with people who are more at risk for dehydration and heat related illness—people with diabetes, people with heart conditions, frail elderly, and a low income population that will not turn on the air conditioning units until they have too (that is, if they have air conditioning at all).  SkepticRD also happens to work in home based health care, which means that my co-workers and I have to be out in that heat (and poorly air conditioned homes) educating our patients and ourselves, and with that comes…..SkepticRD getting a bad case of the cranky pants because of some of the bad information that rears its ugly head (you didn't know cranky pants was a heat related illness did you?).  The following post will hopefully clear up some of the misconceptions people have about hydration, and hopefully help you in Readerland avoid dehydration and heat related cranky pants as well.
1) Myth #1—you must have eight 8oz glasses of water per day.  If you are an origin nerd like SkepticRD, you will be fascinated to know that this myth has been around for over two hundred years.  Apparently a Dr. Christoph Wilhelm Hufeland was interested in how the King of Prussia enjoyed such vibrant health into his 80's, and since he was in the habit of drinking seven to eight glasses of water a day, Dr. Hufeland came to the conclusion that this must be the reason for his health (which, to Dr. Hufeland was a repletion of something called the "life force") and published the results in a book called Makrobiotik. (Link).   This same craze swept through New York's Lower East Side thanks to a women's association that also said it was dangerous for women to get their feet wet. (Link).  One of the other possible origins is that this came from measuring the input (IV fluids) and output (urine) of hospitalized patients in the 1950's. (Link). 
All of this history is fascinating, at least if you're me, But what it comes down to is that there is no scientific evidence to support the eight 8 oz glasses of water per day as a minimum fluid requirement for everybody.  (Link).  One of the things we need to keep in mind is that our fluid requirements vary by body size, gender, activity level, climate we live in, and other health conditions that we have (e.g. a diabetic with poorly controlled blood glucose levels is more susceptible to dehydration).  We also have to consider that many foods, such as fruits, vegetables, and tubers might have a water content of 75-95%, so not all of our fluid requirements are met only by things we think of as being fluid. 
So what do we have to go on?  Not a whole lot.  Most people are being told that they need to be producing urine the color of "weak lemonade" as opposed to "apple juice" colored" to make sure they are hydrated and to be "guided by their thirst."  These statements at least give us some individualized guidelines, which I suppose is better than a blanket statement that has no basis in science, but I'll admit that as a Skeptic I really have trouble stating "just let your body guide you."  Sometimes it seems that my body wants to eat the whole container of Coconut Bliss (my favorite dairy "ice cream" substitute) at one sitting, and if I just let my body guide me I probably wouldn't be at a healthy weight.  I know there are plenty of other health care providers out there who also like to have evidence-based numbers, but the closest we have right now are "the consensus of medical experts," which in this case comes from the Institute of Medicine.  Their review of the data indicates most people get about 80% of our fluid needs from beverages and 20% from food—so their recommendations state that the average male needs for about 13 cups of fluid per day and the average woman needs about 9 cups, and that about 75% of that should come from water.  So is the evidence pointing towards us needing MORE than eight 8oz glasses per day? Maybe.  But for now it looks like many of us will have to settle for a "don't ignore your thirst" and a "look at the urine color" for some sort of assessment of how well hydrated you are. (Link).  Keep in mind the warning signs of true dehydration as well-urinating less than usual, darker colored urine, dry mouth, decreased salivation, dizziness, sunken eyes, rapid pulse and a loss of skin elasticity (pinch your skin—if it stays tented you could be dehydrated).
2) Myth #2—Beverages like tea, coffee, and soda contain caffeine and therefore do not count toward your fluid intake.    Once again I get to bring out my favorite quote from
Paracelsus, "The dose makes the poison."  If you are consuming more than 500-600 milligrams of caffeine per day, which is the equivalent of 5-7 cups of coffee, ~11 cups of black tea, or fifteen 12oz cans of Diet Cokes, you do increase your risk of dehydration.  Now, those of us living in the United States are fond of our excesses, so I have seen people come pretty close to exceeding the limit on coffee and sometimes on tea.  But should you worry about enjoying a large glass of tea on your porch in the late afternoon or forego your cup of coffee in the morning just because it's hot?  No, and there is evidence to back that up. (Link).  Now, keep in mind that if your coffee, tea, or soda of choice is full of sugar, then you are probably going to run into problems with your weight, blood glucose control, and your relationship with your dentist as outlined here in a previous post:
3) Myth #3: If you are thirsty, you are already dehydrated.  My assumption here, is that if you still believe this particular myth, you know nothing about how our bodies evolved to ensure survival of the organism and pass on those beneficial genes to the next generation.  The ability to walk to a faucet and find water that you can safely consume is a relatively recent historical event in human history (available in the late 19th century and "common" in the mid 20th century), and is still considered a luxury throughout the developing world (Yes, I think the history of plumbing is fascinating.  When early human beings got thirsty, it was likely a warning that it was time to start digging, or walk to the nearest water source, or go looking for some fruits and/or vegetables to chew on.  If they were already dehydrated by the time they recognized the sensation of thirst, it is unlikely the human race would have been able to reach a water source fast enough to survive.  Keep in mind also that eating meal that is very salty or food that is very sweet can also trigger the sensation of thirst, but it doesn't mean that you are dehydrated.  (Link)  Now, there may be a few exceptions—sometimes a distance athlete might be so focused on her race that she "blocks out" the thirst sensation and doesn't drink when needed.  But for the rest of us, thirst is just the body's way of saying "go find a source of liquid before things eventually get out of hand.
4) Myth #4: Drinking lot of water helps you lose weight.  I admit, sometimes there really, really are myths that I want to believe, and this is one of them.  What person working so hard to lose weight wouldn't want a to drink a big glass of water or unsweetened tea and Voila: your craving for the French fries have disappeared?  Unfortunately, there is no evidence that this happens.  (Link).  Now, there is still a glimmer of hope here though; apparently if you consume foods that have a high liquid content at your meals, your satiety signals do activate sooner (i.e. you feel fuller faster) and chances are you won't eat as much at your next meal. (Link).  So those of you who like soup might be in luck, but don't expect that extra glass of water to help curb your hunger.
5) Myth #5: We are all in immediate danger of over-hydration or water intoxication. While water intoxication is a valid medical problem, it is unlikely that those of us sipping from our water bottles or iced tea are in any immediate danger.  Those who would be more at risk are:
--Endurance athletes that do not replace sodium after 3 hours of exercise.
--People who drink excessive amounts of water to curb their hunger, particularly on very low calorie diets (see Myth #4).  Sometimes people have been known to consume about 12 cups of water in a short period of time.
--People with psychogenic polydipsia, which is sometimes seen in people with schizophrenia or the developmentally disabled. 
--Babies who have not started on solid food and are given water beyond the fluid found in breast milk or formula.
--Poorly controlled diabetes.  If the blood sugars are uncontrolled, the body will try to rid itself of excess glucose through the urine, so the thirst mechanism is triggered, and people drink excess water.  Sometimes electrolytes are also "washed out" with the glucose in the urine.  Excessive urination should prompt one to seek out medical help anyway.
If you do not fall into one of the above stated categories (or do not have an infant  that falls into the above category) you danger of drinking too much is likely not imminent. (Link).
Take home message—having access to adequate fluid, preferably without added sugars, is important for normal body functions even if it doesn't "cure" anything else.    We need more studies before we can come up with more concrete recommendations on water intake.

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