Alcohol and the Human Body
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Alcohol's Properties
Alcohol is a general term denoting a family of organic chemicals with common properties. Members of this family
include ethanol, methanol, isopropanol, and others. This introduction discusses the physical, chemical, and
physiological aspects of the most commonly ingested of these - ethanol.
Alcohol (ethanol) is a clear, volatile liquid that burns (oxidises) easily. It has a slight, characteristic odour and is very
soluble in water. Alcohol is an organic compound composed of carbon, oxygen, and hydrogen; its chemical formula
is C2H5OH.
Alcohol is a central nervous system depressant and it is the central nervous system which is the bodily system that
is most severely affected by alcohol (see chart below). The degree to which the central nervous system function is
impaired is directly proportional to the concentration of alcohol in the blood.
When ingested, alcohol passes from the stomach into the small intestine, where it is rapidly absorbed into the blood
and distributed throughout the body. Because it is distributed so quickly and thoroughly, the alcohol can affect the
central nervous system even in small concentrations. In low concentrations, alcohol reduces inhibitions. As blood
alcohol concentration increases, a person's response to stimuli decreases markedly, speech becomes slurred, and
he or she becomes unsteady and has trouble walking. With very high concentrations - greater than 0.35 grams/100
millilitres of blood (equivalent to 0.35 grams/210 litres of breath ) - a person can become comatose and die. The
American Medical Association has defined the blood alcohol concentration level of impairment for all people to be
0.04 grams/100 millilitres of blood (equivalent to .04 grams/210 litres of breath). The following is a generally
accepted guide to the effects of alcohol.
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Stages of alcohol intoxication
BAC
(g/100 ml of blood
or g/210 l of breath) Stage Clinical symptoms
0.01 - 0.05 Subclinical Behaviour nearly normal by ordinary observation
0.03 - 0.12 Euphoria Mild euphoria, sociability, talkativeness
Increased self-confidence; decreased inhibitions
Diminution of attention, judgement and control
Beginning of sensory-motor impairment
Loss of efficiency in finer performance tests
0.09 - 0.25 Excitement Emotional instability; loss of critical judgement
Impairment of perception, memory and comprehension
Decreased sensory response; increased reaction time
Reduced visual acuity; peripheral vision and glare recovery
Sensory-motor incoordination; impaired balance
Drowsiness
0.18 - 0.30 Confusion Disorientation, mental confusion; dizziness
Exaggerated emotional states
Disturbances of vision and of perception of colour, form, motion and dimensions
Increased pain threshold
Increased muscular incoordination; staggering gait; slurred speech
Apathy, lethargy
0.25 - 0.40 Stupor General inertia; approaching loss of motor functions
Markedly decreased response to stimuli
Marked muscular incoordination; inability to stand or walk
Vomiting; incontinence
Impaired consciousness; sleep or stupor
0.35 - 0.50 Coma Complete unconsciousness
Depressed or abolished reflexes
Subnormal body temperature
Incontinence
Impairment of circulation and respiration
Possible death
0.45 + Death from respiratory arrest
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Absorption
Alcohol is absorbed from all parts of the gastrointestinal tract largely by simple diffusion into the blood. However
the small intestine is by far the most efficient region of the gastrointestinal tract for alcohol absorption because of
its very large surface area. In a fasting individual, it is generally agreed that 20% to 25% of a dose of alcohol is
absorbed from the stomach and 75% to 80% is absorbed from the small intestine. Because of this peak blood
alcohol concentrations are achieved in fasting people within 0.5 to 2.0 hours, (average 0.75 - 1.35 hours depending
upon dose and time of last meal) while non-fasting people exhibit peak alcohol concentrations within 1.0, and in
extreme cases up to as much as 6.0 hours (average 1.06 - 2.12 hours).
Distribution
Alcohol has a high affinity for water and is therefore found in body tissues and fluids inasmuch as they contain
water. Absorbed alcohol is rapidly carried throughout the body in the blood and once absorption of alcohol is
complete an equilibrium occurs such that blood at all points in the system contains approximately the same
concentration of alcohol.
Elimination
The liver is responsible for the elimination - through metabolism - of 95% of ingested alcohol from the body. The
remainder of the alcohol is eliminated through excretion of alcohol in breath, urine, sweat, faeces, milk and saliva.
The body uses several different metabolic pathways in its oxidation of alcohol to acetaldehyde to acetic acid to
carbon dioxide and water.
Healthy people metabolise alcohol at a fairly consistent rate. As a rule of thumb, a person will eliminate one
average drink or .5 oz (15 ml) of alcohol per hour. Several factors influence this rate. The rate of elimination tends
to be higher when the blood alcohol concentration in the body is very high or very low. Also chronic alcoholics may
(depending on liver health) metabolise alcohol at a significantly higher rate than average. Finally, the body's ability
to metabolise alcohol quickly tend to diminish with age.
Body Weight and Body Type
In general, the less you weigh the more you will be affected by a given amount of alcohol. As detailed above,
alcohol has a high affinity for water. Basically one's blood alcohol concentration is a function of the total amount of
alcohol in one's system divided by total body water. So for two individuals with similar body compositions and
different weights, the larger individual will achieve lower alcohol concentrations than the smaller one if ingesting
the same amount of alcohol.
However, for people of the same weight, a well muscled individual will be less affected than someone with a higher
percentage of fat since fatty tissue does not contain very much water and will not absorb very much alcohol.
Rate Of Consumption
Blood alcohol concentration depends on the amount of alcohol consumed and the rate at which the user's body
metabolises alcohol. Because the body metabolises alcohol at a fairly constant rate (somewhat more quickly at
higher and lower alcohol concentrations), ingesting alcohol at a rate higher than the rate of elimination results in a
cumulative effect and an increasing blood alcohol concentration.
Alcohol Content
It's not how many drinks that you have, but how much alcohol that you consume. As you can see from the chart
below some drinks are more potent than others.
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Alcohol Content of Some Typical Drinks
Drink Alcohol Content
Manhattan 1.15 oz. (34 ml)
Dry Martini 1.00 oz. (30 ml)
Malt liquor -12 oz. (355 ml) 0.71 oz. (21 ml)
Airline miniature 0.70 oz. (21 ml)
Whiskey Sour/Highball 0.60 oz. (18 ml)
Table Wine - 5 oz. (148 ml) 0.55 oz. (16 ml)
Beer - 12 oz. (355 ml) 0.54 oz. (16 ml)
Reduced Alcohol Beer 0.28 oz. (8 ml)
Mixed drinks are based on typical drink recipes using 80 proof liquor.
The amount of alcohol in actual mixed drinks may vary.
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Alcohol Content (in Percent) of Selected Beverages
Beverage Alcohol Content (%)
Beers (lager) 3.2 - 4.0
Ales 4.5
Porter 6.0
Stout 6.0 - 8.0
Malt Liquor 3.2 - 7.0
Sake 14.0 - 16.0
Table wines 7.1 - 14.0
Sparkling wines 8.0 - 14.0
Fortified wines 14.0 - 24.0
Aromatized wines 15.5 - 20.0
Brandies 40.0 - 43.0
Whiskies 40.0 - 75.0
Vodkas 40.0 - 50.0
Gin 40.0 - 48.5
Rum 40.0 - 95.0
Aquavit 35.0 - 45.0
Okolehao 40.0
Tequila 45.0 - 50.5
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The concentration of the drinks that one ingest can have a slight effect on the peak alcohol concentration due to
the differences in absorption rate of different concentrations of alcohol. Alcohol is most rapidly absorbed when the
concentration of the drink is between 10% and 30%. Below 10% the concentration gradient in the gastrointestinal
tract is low and slows absorption and the added volumes of liquid involved slow gastric emptying. On the other
hand concentrations higher than 30% tend to irritate the mucous membranes of the gastrointestinal tract and the
pyloric sphincter, causing increased secretion of mucous and delayed gastric emptying.
Food
Food taken along with alcohol results in a lower, delayed blood alcohol concentration peak (the point of greatest
intoxication). There are two major factors involved in this phenomenon.
First, because alcohol is absorbed most efficiently in the small intestine, the ingestion of food can slow down the
absorption of alcohol into one's system. The pyloric valve at the bottom of the stomach will close in order to hold
food in the stomach for digestion and thus keep the alcohol from reaching the small intestine. While alcohol will be
absorbed from the stomach it is a slower and less efficient transition.
Second and equally important is the fact that alcohol elimination rates are inversely proportional to alcohol
concentration in the blood. Therefore the suppressed levels of alcohol due to food ingestion cause the body to
eliminate the alcohol that is absorbed at a faster rate.
The type of food ingested (carbohydrate, fat, protein) has not been shown to have a measurable influence on this
affect but the larger the meal and closer in time between eating and drinking, the greater the diminution of peak
alcohol concentration. Studies have shown reductions in peak alcohol concentration (as opposed to those of a
fasting individual under otherwise similar circumstances) of 9% to 23%.
Medication
If you are taking any medication, it could increase the effects of alcohol. You should always consult your physician
or the medical information that accompanies the medication when drinking alcohol in conjunction with any
medication.
Fatigue
Fatigue causes many of the same symptoms that are caused by alcohol intoxication. These and other symptoms
will be amplified if alcohol intoxication is concurrent with fatigue.
Tolerance
Tolerance is the diminution of the effectiveness of a drug after a period of prolonged or heavy use of that drug or a
related drug (cross-tolerance). There are two types of tolerance at work with alcohol. The first is metabolic
tolerance in which the alcohol is metabolised at a higher rate (up to 72% more quickly) in chronic users. Because of
the higher metabolic rate for alcohol lower peak blood alcohol concentrations are achieved by chronic alcohol users
than the average drinker when the same amount of alcohol is ingested. The second is functional tolerance in which
there is an actual change in the organ or system's sensitivity to the drug. Studies have shown that chronic alcohol
users can have twice the tolerance for alcohol as an average person. It is important to note however that even in
light of these tolerance factors, it has been shown conclusively that even in heavy alcohol users functional
impairment is clearly measurable at the blood alcohol concentration levels that are currently used for traffic law
enforcement and safety sensitive job performance.
Gender Differences
As outlined above in the section on Body Weight and Body Type different body types coincide with different body
water percentages. In general, but by no means in all cases, women tend to have a higher percentage of body fat
and thus a lower percentage of body water. Therefore, in general, if a man and a woman of the same weight ingest
the same amount of alcohol the woman will tend to achieve a higher alcohol concentration. This, of course, would
not be true if the woman was very fit and the man was somewhat obese, but on average, this is the case.
Furthermore, total body water tends to decrease with age, so an older person will also be more affected by the
same amount of alcohol. According to the table below the differences in alcohol concentration due to average body
composition differences based on gender would be between 16% and 10% depending on age.
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Average Total Body Water
as a function of Sex and Age
Age Male Female
18 to 40 61% 52%
over 60 51% 46%
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Another gender based difference is in the elimination of alcohol. Although not explained, studies appear to show
that women eliminate alcohol from their bodies at a rate 10% greater than that of men.
