Last reviewed February 27, 2013
The other night I saw a commercial in which one of the men in a pickup game of football became thirsty and called time-out. “Luckily” his friend had cold beer on hand. I wondered, “Medical myth? Irresponsible advertising? Beer any good?” I'd always heard that alcoholic beverages were a bad choice if you are thirsty, but I was never sure if that was my parents' propaganda to discourage excessive drinking or whether there was more to it.
It's not intuitive — a cold beer can sure sound (and taste) good when you are hot and thirsty, and at least temporarily, it may seem like a perfect solution. Read on, though, to learn why drinking beer or any other alcoholic beverage may be unwise as a way to quench your thirst.
Imagine you are playing tennis and sweating heavily for a couple of hours in the hot sun. If you sweat enough, the fluids and salt you lose must be replaced. Otherwise, blood pressure will fall, and dizziness, muscle cramps, fatigue and poor muscle function may follow. Your tennis game may suffer, but, more important, you may faint or have other, more serious complications. It's called dehydration, and it can generally be avoided as long as there is access to appropriate fluids.
When water is lost more than salt (as is usually true with sweating), a number of responses occur without your even being aware of them. For example, the blood vessels constrict to maintain blood pressure (even though their constriction may lead to muscle cramps), and a chemical message is sent to the kidney to conserve water. The chemical is anti-diuretic hormone (ADH), which, as the name implies, acts in the opposite way that a diuretic medication works: It helps reduce or prevent water loss from the kidney. In addition, the brain's thirst center kicks in, which leads you to drink water or other fluids.
If you drink a bottle of beer instead of water in the heat of athletic battle, the cold water that makes up much of the bottle will provide some fluid replacement. So far, so good, but one effect of alcohol is that it inhibits the brain's release of ADH. As a result, the kidneys no longer hold onto water as well as they did before you drank the beer. Soon, the kidneys are putting more water into the bladder rather than keeping it in the circulation, as it should under the circumstances. At this point, the situation may go from bad to worse quickly. Alcohol may cause inebriation, a condition that may blunt the senses (so that thirst is not as acutely noticed) and the judgment (so that you may drink more alcohol than you know is good for you). There's the real possibility that your dehydration will worsen rather than improve by drinking beer. Once inebriation and/or dehydration are advanced enough, the ability to sense thirst and obtain water may be increasingly impaired.
So, back to the tennis game: You are playing well, “sweating like a pig” (as my daughter likes to say), and suddenly you're quite thirsty. If you drink a beer or two, ADH release is inhibited, which leads to the kidneys making more (rather than less) urine. Since water loss (through sweat) continues, you may end up with worse dehydration than before you drank the beer. Now you're even thirstier, so you drink another beer. This is going nowhere fast and soon the tennis game is over. Regardless of whether you won, you feel just awful. It is the ability of alcohol to wreak havoc on the body's intricate fluid maintenance system that may contribute to “hangovers” and the feeling of “cotton mouth.” And it can be particularly dangerous on a hot day when ingested as fluid replacement.
You may have other reasons to drink alcoholic beverages (in moderation of course), but don't let excessive thirst be one of them. Drink nonalcoholic beverages when you feel thirsty. Drink extra fluids even if you aren't thirsty in situations where fluid losses are excessive (as may occur with diarrhea or heavy sweating). The elderly must be especially careful because they may not tolerate even mild dehydration well and they may not feel as thirsty as they should for the amount of dehydration they are experiencing.
Entertaining though commercials may be, don't be fooled by medical inaccuracies. After all, the ads are just trying to sell beer, not educate their audience about how best to replace lost fluids.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.