DEAR DR. BLONZ: I have questions about caffeine and alcohol and their effects on hydration. A blog explained that caffeinated beverages are diuretics, and that when you drink 8 ounces of a caffeinated beverage such as tea, coffee or soda, your body will lose 12 ounces of water. That would mean that these beverages are dehydrating instead of hydrating. It made little sense to me, but this was written by people described as experts. Where does alcohol rank as a diuretic? -- M.S., Hayward, California
DEAR M.S.: A word about “experts” on blogs, podcasts or whatever: Have filters in place when you encounter “expert” as a descriptive. Keep the information they offer “on hold” until you are confident of their training and ability to demonstrate an objective, evidence-based foundation for their statements. There are a variety of unaccredited “pay-to-play” organizations selling what appear to be legitimate advanced degrees or proclamations of “board-certified” expertise. Some of these dubious credentials require nothing more than a hefty check, with perhaps a few online courses. Not really what you would assume from one claiming expertise. Some posers are great salespeople -- another red flag being when messages are associated with products being sold.
Diuretics are substances that increase urine output. By this definition, even water could be considered a diuretic. Caffeine is considered to have a mild diuretic effect, but caffeinated beverages such as those you cite would not draw more water out of the body than they contribute. If, however, you were to take caffeine as an over-the-counter or dietary supplement product, it makes sense to be well-hydrated before you start.
The National Academies of Science’s Health and Medicine Division has established a Daily Reference Intake (DRI) for water. The guidelines state that adequate hydration is a daily intake of 2.7 liters (91 ounces) of water for women over the age of 19, and 3.7 liters (125 ounces) for men. Those who are active or live in hot climates may need to consume more. About 80 percent of this total would come from drinking water and other beverages, including caffeinated beverages. The rest comes from food. Vegetables and fruits, for example, are mostly water by weight.
Alcohol also has a mild diuretic effect, but it works differently. One of its effects is to inhibit the release of anti-diuretic hormone (ADH), a hormone that limits the amount of urine produced in the body. When alcohol is around, less ADH is released, which translates to more urine leaving the body. The effects are present in about 20 minutes, which any beer drinker is likely to affirm.
Alcohol’s diuretic effects play an interesting role, and many of alcohol’s effects depend on the blood concentration of its metabolites. The body has a rate at which it processes alcohol, and it uses its fluids as a storage queue for metabolic byproducts awaiting processing and elimination. As such, alcohol’s diuretic effect enhances the consequences of over-consumption.
Tolerance to alcohol is said to be weight-related: The larger you are, the more you can tolerate. This is not so much because larger individuals metabolize alcohol faster, but because a larger body has a greater blood volume to begin with.
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