The Brain and Alcohol


Alcohol is easily and quickly absorbed into the body This process begins before the drinker even swallows a sip of beer or wine because 5 to 10 percent of alcohol is transferred to the bloodstream directly through the lining of the mouth. The beverage then passes through the stomach and small intestine, where a high concentration of small blood vessels speeds absorption into the bloodstream. As alcohol moves into the bloodstream, it spreads throughout the body. However, its effect on the brain is almost immediate. There are two reasons for this: a substantial portion of the blood that the heart pumps goes directly to the brain, and the brain’s fatty material readily and easily absorbs alcohol.

People have understood for thousands of years that drinking beer, wine, and liquor makes them intoxicated, but it was not until the last two decades of the twentieth century that scientists discovered how alcohol actually does this. As late as 1974 the National Institutes of Health (NIH) issued a report saying, “No one knows how alcohol intoxicates [people].” But by 2000, in its Tenth Special Report to the U.S. Congress on Alcohol and Health, researchers for the NIH and its National Institute on Alcohol Abuse and Alcoholism (NIAAA) finally had the answer: “The changes in behavior seen soon after consumption of alcohol — as well as the euphoria and anxiety reductions seen with alcohol — all result from alcohol’s actions on the brain.”

How Blood Alcohol Levels Rise

How intoxicated people become when they drink depends on how fast their liver can process alcohol. A normal, healthy liver can break down and eliminate 0.5 ounces of pure alcohol from the bloodstream each hour, which is the equivalent of 12 ounces of beer, 5 ounces of table wine, or 1.5 ounces of 80-proof distilled spirits. When people drink more than those amounts in an hour, their blood alcohol levels (BALs) will go up; if the levels rise high enough, they will become drunk. The following is an example of how this happens, taken from Beyond the Influence: Understanding and Defeating Alcoholism.

If s a Sunday evening in Denver, the Broncos have just won the Super Bowl, and Joe is in a party mood. Around 8 p.m. he joins some friends at a local tavern, and in the next four hours he downs twelve beers and four shots of 80-proof tequila. In all the excitement, Joe, who weighs 165 pounds, forgets to eat dinner, munching on pretzels and potato chips instead. By midnight, when Joe falls into bed, his liver has burned up 2 ounces of pure alcohol (about four beers). By 6:00 a.m., when he wakes up, his liver has eliminated an additional 3 ounces (six more beers). On his way to work at 7:00 a.m., Joe still has approximately 2 ounces of pure alcohol circulating around in his bloodstream (the remaining beers and 4 ounces of tequila). Seven hours after Joe stopped drinking, he is still legally drunk. Unfortunately for Joe, there’s nothing he can do to nudge his liver along and accelerate the metabolic process. Coffee, cold showers, fruit juice, and exercise are all basically useless, for the fact remains that if you drink more than your liver can process at one time, your [BAL] will rise. If you keep drinking, you’ll get drunk. And the more you drink, the drunker you’ll get.

The brain and spinal cord make up the central nervous system, which controls physical behavior like walking as well as involuntary actions necessary for life, such as breathing and the beating of the heart. The central nervous system runs along the spinal cord and branches out into every part of the body. The brain is in continuous direct communication with all of these parts, sending messages through this system to control its actions. These directives, which are in effect commands to various muscles and parts of the body, pass between individual cells via what are called neurotransmitters.

The latest research on drinking shows that alcohol interferes with this flow of commands from the brain at the level of the neurotransmitters, and that this disruption of communication from the brain is the major change that causes intoxication. Thus, intoxication is caused by alcohol working directly on the brain to dull or hamper the way it works.

Intoxication is a gradual process; it does not occur after a person has consumed one drink but several. This is because alcohol in the bloodstream has to build to sufficient levels to start affecting how the brain operates.

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