Article By: Harvey Finkel, MD
All of us must wonder sometimes what happens to the alcohol we drink. How much consumed translates to what blood alcohol concentration (BAC)? What might be the effects, good and bad, on various body organs and functions? How much might it take to get us in trouble with the law? There are no crisp single answers, but a recent piece in aim digest online (March, 2O11) set me thinking.
All I am about to reveal concerns the nonexistent ideal human subject. Be aware that a host of factors cause variance in this complex. Sex counts: the enzyme alcohol dehydrogenase, which starts the neutralization of alcohol, is only 6O percent as abundant in the stomachs of women as compared to men. This and other differences (proportionally more body fat in women, in which alcohol is poorly soluble, and less water, in which it easily disperses) mean that women absorb more of the alcohol they drink. Studies and experience have shown that, drink for drink, women suffer more damage from drinking excessively than do men. Size, medications, diseases, and whether one drinks regularly can strongly influence the effects of alcohol. One who regularly drinks heavily can sustain without apparent impairment levels of blood alcohol that would be likely to induce coma, even death, in a person previously innocent of alcohol – the miracle of adaptation. Inherited differences in detoxifying enzymes can dramatically alter alcohol tolerance. As many as half of some east Asian populations are hypersensitive to alcohol on this basis. The effects of aging on alcohol tolerance, however, have been exaggerated. Attaining seniority is no reason for abstinence.
While one can change size, sex and inheritance only with great difficulty, what can we change that might make a difference? The amount and rate of drinking are the most obvious answers. According to the Massachusetts State Police, each standard drink of whatever beverage likely raises the blood alcohol concentration by about O.O2 percent, an admittedly very rough approximation. A standard drink is 5 ounces of wine (2.8 grams of alcohol per ounce), 12 of beer, or one shot of average spirit. Adjust for stronger or bigger drinks. The legal limit for driving, if over 21, is O.O8 in all states. This means O.O8 grams of alcohol per 1OO milliliters of blood. Eating is a big influence. Normally about 2O percent of swallowed alcohol is rapidly absorbed from the stomach (less the portion neutralized there), and 8O percent even more rapidly from the small intestine. Food causes considerable delay in the emptying of the stomach into the small intestine. Also surprising, eating a balanced meal before, during or even soon after drinking boosts the rate of disappearance of alcohol from the blood. Exercise, vitamins, caffeine, and sugars other than fructose, contrary to urban legend, have no effects on alcohol metabolism.
What happens to the alcohol we do absorb? Ninety percent is broken down, eventually to carbon dioxide, water and energy, at a steady rate. The remaining ten percent is excreted unchanged in urine, expired air and sweat. The first step in the breakdown, catalyzed by alcohol dehydrogenase, leads to very toxic acetaldehyde, which most of us are able to rapidly convert to harmless products by the action of another enzyme, acetaldehyde dehydrogenase. Here is where the Asians with defects in this enzyme system get into trouble. Unable to easily get rid of acetaldehyde, they quickly accumulate the nasty stuff, which makes them sick: flushed, drowsy, pounding heart, or worse. Data originating more than 9O years ago indicates that the blood alcohol elimination rate for concentrations of O.15 percent or greater is O.O2 per hour. For lower BACs it’s O.O15 per hour. These are averages. For safety’s sake, O.O1 per hour has been recommended as the rule of thumb, which means that each drink consumed takes nearly two hours to be cleared.
The main site of breakdown of absorbed alcohol is the first stop after gastrointestinal absorption – the liver – an awesome chemical factory. Other tissues participate to a limited degree. Drinking itself or certain drugs, e.g., phenobarbital, tend to induce the enzymes to work harder, but a liver damaged by alcohol abuse would be less able to cope, and phenobarbital would add to alcohol’s sedating effect. There’s always a catch. The liver is the canary of alcohol consumption, the first organ to show the damage of excess. Liver mavens estimate that a daily dose short of about 42 grams of alcohol (15 ounces of table wine) can be tolerated by men without lasting liver damage, half that for women.
Prevalent recommended medically safe limits are no more than two or three drinks per day for men, half that for non-pregnant women, preferably with food. This presupposes no relevant medical conditions and that you’re not about to pilot a plane, cut a large diamond or perform brain surgery. No binge drinking! Saving up your weekly allowance for Saturday night is especially dangerous. I remind you also that moderate drinking is healthful; abstinence may be a health risk.