DEAR DR. BLONZ: I have a question about water. Is it a good idea to drink more water than you normally feel like, or is it sufficient to drink only when you're thirsty? -- S.T., via email
DEAR S.T.: Let's look at all that water does. Humans require more water than any other nutrient. We can survive for weeks without food -- though I'm not sure I'd call that living -- but only a few days without water. Our dependence relates to the fact that we are a water-based form of life: It makes up 95% of our blood, 83% of our lungs, 73% of our brain and 60% of the body as a whole. Even our bones are about 30% water!
Water is vital to every cell, as it is the environment in which biochemical reactions take place. Water is the medium for dissolved substances going in all directions: nutrients, hormones, fuels, medications and biochemical components headed toward their places of action; toxins waiting in queue to be broken down; and metabolic waste products on their way to disposal. Sufficient water is also vital to maintaining our blood pressure.
The water in our tissues keeps our body temperature relatively constant. This is important because essential organs, such as the brain, are sensitive to changes in temperature. Aside from buffering the external effects of climate, water helps the body release heat produced internally from muscular work and biochemical activity. When the body needs to chill, it relies on evaporation -- a process that casts off excess heat by exhaling water vapor through the lungs, as well as the cooling effect of perspiration on the skin.
Given all this, it is no wonder that dehydration, defined as a harmful reduction in available body water, would be inconsistent with good health.
Back to your question about whether it's OK to only drink when you're thirsty. How reliable is our sense of thirst?
As fluid volumes decrease, the concentration of dissolved substances rises. The body has sensors to detect such changes; it's a critical regulatory element, as chemical reactions have concentration tolerance limits. The urine is the main way we eliminate unwanted water-soluble items, but there are limits to how much the kidneys can concentrate the urine. Severe water loss can become life-threatening, so once detected by sensors, substances get released to halt water loss and stimulate thirst.
Thirst is an initial sign you are getting dehydrated; by the time the sensation of thirst is stimulated, fluid levels are already on the wane. Another critical issue is that the precision of our thirst sensors decreases in adults over 50, which places the elderly at increased risk for dehydration if they only drink when thirsty. Given all this, I am not sure it is best to wait.
Some general rules are to drink water with meals and to pre-hydrate before being physically active, or more often if you are in a warm climate. Another general rule is to check your urine output; it's normal to urinate about six to eight times a day. Normal urine should be colorless or straw-colored, whereas more concentrated urine is darker in color.
The former view that everyone should drink eight glasses of water a day is not solid science. We all need to find the formula of food, fluids and hydration self-awareness that works best. In the scheme of things, consider a plant-based, whole foods diet to be your hydration ally; fresh foods tend to contain a bunch of their own water.
Read more on water at b.link/ug3rd8 and b.link/q84c4c.
Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.