“Officer, the Breathalyzer must be wrong. I only drank two glasses of Chardonnay,” the young woman complained. “How is that possible?” Well, it is possible.
Absent from the controversy about wines with high alcohol content–those over 14 percent–is the effect these wines have on blood alcohol level. Many winemakers and consumers don’t even consider the effect, or discount it if they do consider it. When discussing this topic with consumers, and even winemakers, I’ve often been told that an additional one or two percent is “trivial.” Hearing this, the image that pops into my mind is that of an ostrich with its head in the sand.
It’s hardly trivial! Going from drinking two glasses of wine with 12 percent alcohol to a similar amount of wine that contains 14 percent alcohol could put you from under to over the legal limit for driving. And as the wine’s alcohol content increases from 12 to 15 percent (a 25 percent jump), average blood alcohol levels can rocket up 35 percent, as shown in the table below.
Still, it’s not just what you drink or how fast you drink it that determines blood alcohol level. Gender can be a factor, along with whether you eat or not. Moreover, your age, as well as whether you’re a daily or sporadic drinker, can influence the Breathalyzer.
Although the liver breaks down most of the alcohol we consume, alcohol metabolism really starts in the stomach, where an enzyme called alcohol dehydrogenase, similar to the ones found in the liver, is located. Women have less of this stomach enzyme (or it works less well because estrogens inhibit it) than men. As a consequence, women break down less alcohol in the stomach than do men, which means, everything else being equal, they will have higher blood alcohol concentration (BAC) despite drinking an equal quantity. Some scientists believe that the amount or activity of this enzyme decreases with age, which might help explain why individuals become less tolerant of alcohol as they age.
Alcohol is distributed only in the portion of the body that is composed of water, as opposed to fat. Since men’s bodies contain a higher proportion of water than women’s, the same amount of alcohol will be dispersed in a larger volume resulting in a lower BAC for male drinkers.
The stomach pushes its contents into the small intestine, where most of the alcohol is absorbed. It empties more slowly when it’s filled with food than when empty so drinking wine while eating means the alcohol stays in the stomach longer where it can be broken down. The urban myth that eating butter before drinking “protects” the stomach against the direct irritating effect of alcohol is not true, but eating before or while drinking will certainly result in a lower BAC than when drinking on an empty stomach.
The rate at which the stomach empties might explain the additional buzz people describe from drinking Champagne or sparkling wine. Many had assumed that Champagne made people woozy faster because of the setting in which it was usually consumed—quickly, on an empty stomach. But in 2003 British researchers showed that the blood alcohol level is higher after people drink Champagne than after they drink the same amount of de-fizzed bubbly. A reasonable explanation is that the carbonation promotes gastric emptying and thereby reduces the time the alcohol remains in the stomach where it can be metabolized.
Daily or Special Occasion
The liver is the major site of alcohol metabolism, but not all livers–not even normal ones–are the same. Whether a person’s been drinking daily or sporadically determines how efficiently the liver breaks down alcohol because the enzymes responsible for metabolizing alcohol are inducible. That means that drinking one to two glasses of wine daily tells the liver to recruit more enzymes–rev-up the factory–to break down the alcohol. Consequently, someone who drinks daily is capable of metabolizing more alcohol than someone who drinks only on the weekends. Everything else being equal, the chronic imbiber will have a lower BAC than the sporadic drinker because the liver has more enzymes available and ready to break down the alcohol.
Most daily wine drinkers recognize this phenomenon without realizing it when they have a brief illness, such as a cold, and temporarily avoid alcohol. After a week of abstinence, the first glass of wine has a bigger impact on how you feel than usual. That’s because after a week of not drinking, the liver is out of practice. With that first glass of wine, it’s unprepared for the work and is overwhelmed. It can metabolize less alcohol so more pours into the blood stream.
Of course the most important factor in determining BAC is the alcoholic content of what you drink and how fast you drink it. Drinking beverages with a lower alcoholic content slowly over a longer period of time results in a lower BAC. That’s because the more slowly alcohol is presented to the enzymes–whether they are in the stomach or liver–the more efficient they are in breaking it down before it reaches the blood stream.
Obviously, drinking 80-proof (40 percent alcohol) spirits will increase BAC more than drinking wine. But what’s less apparent is that even small differences in the alcoholic content of wines can make a big difference in BAC. (See table below).
The Bottom Line
A 200-pound male who drinks wine regularly and has just consumed two glasses of wine during an elaborate meal eaten leisurely over two hours will have a BAC level that is dramatically lower than that of a 130-pound woman who drinks only occasionally and has polished off those two glasses of wine quickly.
But, as the table shows, if the young woman who was stopped by the officer was drinking white Burgundy or Riesling that contained 12 percent alcohol instead of a California Chardonnay with 14 percent alcohol she would have passed the Breathalyzer.
The following table is taken using the formula from a website called globalRPh that allows calculation of blood alcohol concentration (BAC). These calculations are only rough estimates because the formula does not account for individual differences in how the liver metabolizes alcohol. Individuals should not rely on these values or any online calculators for determining whether it is safe or legal to drive.
The table below is for an average 130 lb woman who consumes two 5 oz glasses of wine over 1.5 hours.
Note that while the alcohol content of the wine rises 25% (from 12 to 15%), the blood alcohol concentration goes up by a greater proportion, 35% (65 to 88 mg/dl). As more alcohol hits the stomach, more of it gets through into the blood.
Alcohol content Blood alcohol concentration
0.080% is the legal limit for driving in the United States.
Questions or comments? Email me at firstname.lastname@example.org
[Editor’s Note: The author is a gastroenterologist at the Beth Israel Deaconess Medical Center in Boston and as Assistant Professor of Medicine at Harvard Medical School. M.F.]
January 10, 2012