If you drink, you most likely want to drink reasonably and responsibly. But what are the factors that can help you keep a confident check on your blood-alcohol content—and your mental faculties—so you don't embarrass yourself or, worse, hurt yourself or others?
According to the CDC and the National Institute on Alcohol Abuse and Alcoholism, a number of variables go into the answer: your body weight; amount of muscle or fat you have; your gender; your age; the other chemicals in your drinks; how fast you are drinking; the amount of food in your stomach; your drinking history; your tolerance to alcohol; other drugs in your system; your general health; and your emotional state.
Alcohol usually is absorbed from the gastrointestinal tract within 30 to 60 minutes after you drink it. Your stomach absorbs about 20 percent, and the remainder is absorbed in the small intestine. About 10 percent of alcohol is eliminated from your body by the kidneys and lungs. The amount of alcohol exhaled through the lungs is used to accurately estimate blood alcohol concentration. Inexpensive electronic devices that measure exhaled alcohol to estimate blood levels are available from stores.
For most people, getting your blood alcohol level to the point of being legally intoxicated occurs after approximately two drinks for an average size woman and three drinks for an average size man. An average drink is 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proof liquor and contains approximately 15 grams (one half ounce) of pure alcohol. Your body metabolism processes about one average drink an hour.
Alcohol is absorbed into the bloodstream and dissolves in the body's water. It is a depressant that inhibits responses of the central nervous system. In small quantities, it can impair coordination and thinking. In large quantities in a short period of time, it can be fatal. Excessive amounts over a long period can cause liver damage.
The extent of alcohol's effect on the central nervous system depends upon how much is in your blood and how much blood you have. Two of the main determinants for that are body weight and the amount of water in your body. Women have less body water than men of similar body weight, so a woman will tend to have a higher blood alcohol level than a man of the same weight after drinking the same amount of alcohol. As a person ages, body water usually decreases and body fat increases, so blood alcohol levels will be higher in older people.
Because your body size determines the volume of blood and amount of water in your body, smaller people usually will have higher blood alcohol levels if they drink the same amount of alcohol as a heavier person.
Men and women
Due to the way a man can metabolize alcohol, men generally can drink more alcohol than women of the same size.
A woman's body also absorbs and metabolizes alcohol differently from a man's, according to the National Institutes of Health. Women have higher blood alcohol levels than men do after consuming the same amount of alcohol. Women also are more susceptible to alcoholic liver disease, heart muscle damage and brain damage. Women are affected more because of their lower levels of body water and because the stomach enzyme ADH, which metabolizes alcohol, is not as active as in men.
Because people lose muscle mass and it is replaced by fat tissue as they get older, they will have higher blood alcohol levels when they drink alcohol compared to younger people of the same weight.
Other chemicals in the drink
The carbon dioxide in champagne increases the rate of absorption of alcohol causing a more rapid effect.
Speed of drinking
The body can generally metabolize about one average drink (15 grams or one half-ounce of pure alcohol) every hour. If you chose to have more than one drink per hour, your blood alcohol level will continue to rise. One beer or one shot of alcohol or one glass of wine is equal to about a half ounce of pure alcohol. The metabolic rate is not affected by physical activity, drinking coffee, or drinking more nonalcoholic beverages.
Food in stomach
If you eat an average meal before drinking, the absorption of the alcohol will be slowed considerably—by up to an hour or more initially. But this effect is temporary.
The type of food consumed also is a factor in slowing the absorption of alcohol. The more fat in the meal, the longer it will take the stomach to process the food and the slower the absorption of alcohol.
Drinking history, tolerance
Tolerance means that it takes more alcohol to produce the same effect or achieve the same blood alcohol level. This sometimes occurs in people who drink heavily and often. Their bodies metabolize alcohol slightly faster than moderate drinkers. On top of that, the chronic users' organs sometimes develop less sensitivity to alcohol, so the actual effects of the same alcohol blood level for them would be less than for the casual drinker. But the destructive effects of alcohol on the liver and other parts of the chronic user's body can be devastating over time.
Alcohol reacts negatively with more than 150 medications, according to the National Institute on Aging and National Institute on Alcohol Abuse and Alcoholism. Common examples include most sedatives, antianxiety pills, sleeping pills, antidepressants, antibiotics, blood thinners, and anticonvulsants (seizure medications). Check with your doctor before drinking alcohol with any medication.
Physical and emotional health
People who are fatigued or highly stressed out usually will have a noticeably stronger reaction to alcohol, possibly feeling greater depression or some other exaggerated response to normal levels of alcohol.
Because the effects of alcohol usually are subtle at first, you may not recognize that your awareness and responses are compromised.
Examples of drink equivalence
The NIAAA has developed information on standard drink equivalents and the number of standard drinks in different container sizes..