I received a message from a reader the other day taking me to task for the information I posted in the post about Endurance Tips last November. More specifically, he took exception to the following suggestion that I passed along from the Cirrus pilot who had just completed a daylight hours run from Florida to California.
Hydrate heavily (to the point your urine is clear and not colored) for days before the trip
While I must admit, I am not a physician the advise seemed to make sense. This is even backed up, to a certain extent, by inforamtion passed on to media “riders” before Blue Angel flights. They encourage that the individual drink water until it hurts, and then drink some more, the day before their media flight.(Note: This inforamtion gleaned from the Airspeed Online podcast. I’ve not been blessed to take a ride with the military yet. Or at least not in a jet..)
Here is Juan’s counter-point to the statement above:
I was reading your blog on the Cirrus driver making a California to Florida trip. One of the things the pilot did was hydrate heavily on the days preceding his flight until his urine became clear. Many people (including sports coaches and athletes) believe that drinking fluids until your urine becomes clear is a good idea. This is BAD advice for pilots and athletes alike.
To explain this, I must give you a crash course on how kidneys work and tell you what they can and cannot do. Kidneys filter blood. This filtrate can do one of two things. Either it can be reabsorbed back into the blood stream, or it can be excreted as urine. When you are dehydrated, your kidney will try to reabsorb more filtrate to try to maintain blood pressure. (if all that filtrate gets to your bladder, then your dehydration status will only get worse, right?)
CONCEPT #1: Your kidneys have a limit to how much they can reabsorb. So, if you are stuck in a desert without water, your kidneys will continue to excrete urine because it just can't reabsorb all of the filtrate - it is just not efficient enough.
CONCEPT #2: Your body does not store extra water!!! If it did, you would be in the hospital with swollen legs and shortness of breath! (actually, this is a salt retainment problem but lets not go there) So, you can drink all the water you want, but anything considered excess by your body WILL get excreted! PERIOD! (and this happens constantly!)
CONCEPT #3: When you're getting really dehydrated, your kidneys respond to a hormone called ADH that allow it to absorb a bit more of filtrate. Think of it as a nitrous boost in a race car. It gives it that last umph of performance.
KEY POINT: If you drink an excess of water for a prolonged period of time, your kidneys will not be able to react to this hormone. Why? Because this hormone works by opening pores in something called the collecting duct of the kidney that allows water to flow back into the interstitium of the kidney by a process called osmosis (and hence back into your blood where you want it when you're dehydrated). However, the water will only flow back into the interstitium if there are ions there. If you drink water for several days, ions in the interstitium get depleted, and the driving force for this reabsorption disappears. Hence, you will have to drink water sooner! Don't believe me? See how many times you get up to urinate in the middle of the night if you drink water all day!
In short, one should drink water when one is thirsty! It is true that some people might have to drink a bit more water than this to be hydrated (some people are less sensitive to thirst than others). But constantly drinking water for days is not a good idea if your goal is to stay hydrated. As long as you have a good supply of water on the plane, you should be fine whether you've drank water in the preceding days or not. All you're doing by drinking water excessively for the preceeding days is making you feel the urge to pee come a little sooner and make you become dehydrated faster.
Perhaps the key differentiator is the short-term benefit of doing this the day before as opposed to doing it for days before-hand. There is no doubt at all that dehydration as a pilot is bad as it affects your performance and your decision-making skills The question seems to be about how to accomplish the goal.
Do we have any doctors (pilots or otherwise) who might like to offer up an opinion here? As always, we encourage people to use the comments section below so we can carry on this discussion in public. You can post anonymously if you prefer!
Tags: tips, endurance