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TP 1535 E

The ABCs of Alcohol

How much is to much? When have you crossed the line? While alcohol affects everyone a bit differently, there are factors that apply to everyone. Understanding the principles will help you to make informed and intelligent decisions about alcohol.

• How Breathalysers Work
• Alcohol and Your Body
  • What Goes In ...
  • ... Must Come Out
  • The Black Coffee Myth (and Other Acts of Futility)
  • Size Does Matter
• How Much Can I Drink and Still Be Safe to Drive?

How Breathalysers Work

The term blood alcohol concentration, or BAC, refers to the amount of alcohol in a person’s blood. In Canada, BAC is usually expressed as the weight of alcohol in a given volume of blood.  Canadian law specifies that the maximum allowable amount of alcohol in the bloodstream of a driver is 80 milligrams in 100 millilitres of blood — 80 mg% or .08. 

BAC can easily be measured in a person’s breath by using a breathalyser.  As blood flows naturally through the lungs, the alcohol molecules pass into the air in the lungs.  When a person blows into a breathalyser, these alcohol molecules are expelled with the air and the concentration of alcohol in the blood can be measured.  This is as accurate as a blood test. 

The more you drink, the higher your BAC.  The higher your BAC, the more physically and mentally impaired you become.  The more impaired you are, the higher your risk of a crash.  If you drive with a BAC over .08, you are impaired and you are breaking the law.

Alcohol and Your Body

Many of us enjoy having a drink, whether as part of a meal, at a social gathering, or simply to relax. However socially acceptable this is, we should keep in mind that alcohol is to be used with understanding and care, and only under suitable circumstances.  Knowing alcohol’s effects is just as important as reading the instructions and warnings on a bottle of pills.  It is basic preventive medicine to know how your body handles alcohol. 

Spirits, wine and beer differ in their concentration of alcohol.  For example, most beers contain 5% alcohol, wines 11-12% and spirits 40%.  Even though a bottle of beer is generally larger than a glass of wine or a shot of liquor, standard servings of these various types of beverages contain the same amount of alcohol — about 13.5 grams. 

It is important to recognize, though, that some beers contain more than 5% alcohol, while some contain less.  And if you don’t use a shot glass to measure your liquor, you could be drinking more alcohol than you think.

What Goes In ...

When you have a drink, the alcohol is absorbed directly into your bloodstream through the stomach and small intestine.  The more you drink, the more alcohol will be absorbed, and the higher your BAC will rise. Given enough time — typically 30 to 90 minutes or longer — alcohol is distributed evenly throughout your body.

... Must Come Out

Like most things we eat or drink, alcohol must be broken down and eliminated.  It takes much longer to eliminate alcohol from your body than it does to drink it.  Most alcohol is destroyed by a process called oxidation, which breaks alcohol down into carbon dioxide and water.  More than 90% of the alcohol is oxidized in the liver.  The rest is eliminated, unchanged, through the lungs and kidneys.  The liver’s capacity to break down and dispose of alcohol is limited — it takes just under two hours for a standard serving of alcohol.  

As you drink, alcohol is absorbed into your bloodstream and your BAC rises quickly to a peak.  If you stop drinking, your BAC levels off.  It can remain the same for as long as an hour or two because alcohol is entering your bloodstream at the same rate as it is eliminated.  Your BAC will then decline steadily by approximately .015 per hour.  It is important to remember that your BAC can rise much more quickly than it falls.

The Black Coffee Myth  (and Other Acts of Futility)

You can’t dance, jog, sing, cry or urinate away alcohol.  Contrary to popular opinion, drinking black coffee or taking a cold shower will have no effect on your BAC.  Only a very small amount of alcohol is eliminated through tears, saliva and perspiration.  

If you have a BAC of .09, it will take you about six hours to return to a BAC of 0.  You can’t do anything to speed up the elimination of alcohol.  The experienced drinker takes almost as long to eliminate alcohol as does the inexperienced drinker.  Only time can lower your BAC.

Size Does Matter

Your peak BAC will depend on your weight, because blood volumes (or more precisely, body water) differ according to body weight and size.  If two people consume the same amount of alcohol, the individual with the greater blood volume will have a lower concentration of alcohol.  Blood volume varies according to two basic factors: body weight and the type of body tissue that makes up that weight.  Larger persons generally have a greater volume of blood in which alcohol can be distributed.  After drinking the same amount of alcohol, a person weighing 68 kg (150 lb.) will generally have a higher peak BAC than a person of the same sex weighing 80 kg (175 lb.).  

Muscle tissue contains larger amounts of blood than fatty tissue.  The more muscular or lean your body is, the greater volume of body water there is in which to distribute the alcohol you drink.  After drinking the same amount of alcohol, a person who weights 80 kg (175 lb.) but has a lot of body fat will reach a higher BAC than a lean 80-kg person of the same sex.  

Women tend to have a higher proportion of fatty tissue than men and, as a result, a lower volume of body water.  Equal amounts of alcohol will, therefore, result in a higher BAC for a 60-kg (130-lb.) woman than for a 60-kg man.  When you also consider that women are generally smaller than men, the differences in BAC between men and women can be profound.  Women should not assume that they have a lower BAC than a man simply because they have had fewer drinks.

How much can I drink and still be safe to drive?

Some people suggest you limit your alcohol intake to one standard drink per hour.  Unfortunately, this rule works only for the first few hours and generally only for men.  When you drink, you begin to lose your ability to recognize signs of intoxication.  Most people can’t judge how impaired they are after drinking and can’t accurately estimate their own BAC without the aid of a breath-testing instrument.  Therefore, when you have any doubt about your level of impairment or your BAC, you shouldn’t drive.

Impairment begins soon after you start drinking.  You can reduce the risk of being involved in an accident, however, by drinking moderately.  A good rule is to restrict your consumption to no more than two drinks an evening.  The more you drink, the greater your level of impairment and the higher your risk of death or injury.

You are safest if you completely separate driving from drinking.