Philip J. Goscienski, M.D.
Dehydration — letting your body get behind on its need for water — is one of the most common reasons for hospitalization among seniors and a leading cause of kidney stones. Persons who have a habitually low intake of water seem to be more prone to cancers of the bladder, kidney, prostate and testicle.
Physicians classify dehydration by the percentage loss of body weight. If you are 1 percent dehydrated you'll notice it. At 2 percent your friends will notice it and at 5 percent the folks in the Emergency Department will notice it. Our tolerance for water loss is very small and a substantial number of adults are mildly dehydrated much of the time, according to a study done at Johns Hopkins Hospital.
Thirst isn't always a good measure of whether or not we need water, especially as we get older. What we perceive as hunger may be a need for water, not calories. Babies show mild dehydration by acting fussy; adults develop fatigue or fuzzy thinking.
Sweating isn't a reliable gauge of water loss either. In the low humidity of the Southwest water evaporates from the skin so quickly that you might not notice. When you exercise enough to sweat you also lose more water through your lungs. A bout of diarrhea will quickly deplete your body of water and it's especially dangerous at the extremes of age. Dehydration used to be the most common cause of death in infants in the United States and it still is in undeveloped parts of the world. When seniors become dehydrated their blood becomes thicker and more likely to clot. When that occurs within a blood vessel of the brain or heart the result is a stroke or a heart attack.
Forget the usual advice for water intake. The recommendation of eight 8-ounce glasses a day for an adult makes no sense for someone who is working hard outdoors on a sunny July afternoon. Under any conditions the best indicator of water balance is the color of your urine. It should always be pale yellow. Dark urine with a not-so-subtle odor is a sign of inadequate water intake. That's no problem when it only occurs occasionally; it is not an acceptable daily pattern.
You'll need to replace more than water if you engage in more than about 45 minutes of heavy exercise. Salt depletion will make the water loss worse. It's a good idea to have a sports drink handy at those times in order to replace losses of salt and to restore energy with carbohydrate in the form of sugar.
At an altitude over about 5,000 feet, whether in an airplane or an automobile, you will experience additional but subtle fluid loss. Caffeinated and alcoholic beverages make the problem worse. Prolonged sitting in one position during air or road travel and dehydration combine to raise the chances that blood clots will form in the legs and cause local pain. When such deep vein thrombosis occurs a clot can break loose and do serious mischief elsewhere.
You might be overdoing water intake if your urine is always clear and almost odorless. Water overload can lead to serious problems in persons with inadequate kidney function and in athletes who do not keep up with salt requirements. As in most areas of living, moderation is the key.
Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at firstname.lastname@example.org.