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The information presented here relates to the properties of alcohol, its consumption, and the effects that it may have on the bodies of individuals. This section is intended for a broad audience and can be used and adapted to provide basic guidance for the public regarding drinking. It can also be used to educate the general public or particular groups about alcohol consumption—for example, by incorporating it into health information provided through school curricula.
What is "alcohol"?
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The word "alcohol" derives from Arabic al-kuhul and is applied to the many members of the family of alcohols. The one found in beer, wine, and spirits is called ethanol or ethyl alcohol. It is a simple molecule with the chemical formula C2H5OH, often abbreviated as EtOH. It is the presence of the –OH combination (the hydroxyl group) attached to a carbon atom that makes a molecule a member of the alcohol family.
The simplest form of alcohol is methanol (methyl alcohol, CH3OH), sometimes also called "wood alcohol" because it can be produced by fermentation of wood. Other members of this family include glycol (found in anti-freeze for cars), propanol or propyl acohol (rubbing alcohol), and cholesterol, a complicated molecule vital for many bodily functions and which, in excess, can cause serious illnesses such as heart disease.
Effects of alcohol
Ethanol is the most famous member of the alcohol family, consumed by humans throughout recorded history. Alcohol is enjoyed by many people around the world because of its relaxing properties, as an enhancer of sociability, and as a complement to meals.
For all its positive effects, ethanol can also create problems for individuals who drink it irresponsibly and in excess. Much of this has to do with the intoxicating properties of alcohol, but too much alcohol can also harm the body in other ways.
Alcohol has intoxicating effects. Ethanol is best known for producing drunkenness. However, drinking methanol, for example, also leads to intoxication and has dangerous consequences. Methanol is broken down by an enzyme that converts it into formaldehyde, a chemical used to preserve biological specimens. Since this enzyme is present in the human eye, the formaldehyde "fixes" the eye tissue, causing permanent blindness. Drinking even small amounts of methanol is extremely dangerous and can kill you.
Methanol is sometimes found in beverages that are not carefully controlled for quality. Such beverages may be produced by those who are outside the legal market, or accidentally by "home producers." Methanol contamination has been known to poison and kill several hundred people in a single incident.
The chemistry of ethanol
An interesting characteristic of ethanol is its very small size in comparison with the other molecules with which it interacts in the human body. However, each one of these tiny molecules has the power to affect the body’s biochemistry.
Another characteristic of the ethanol molecule is that it carries a small electrical charge, which is crucial to its behavior in the body. Its slightly negative charge allows ethanol to react with the slightly positive charge on a water molecule, allowing it to dissolve. Since ethanol mixes well with water, it can easily penetrate our water-filled human bodies and pass into the blood stream.
Ethanol is also soluble in oils. This means that ethanol can easily pass through the membranes of cells, which are made largely of fat molecules.
Thus, ethanol can roam freely throughout the body. Because it dissolves easily in water, it is rapidly absorbed from the digestive tract and mixes easily with blood; because it also dissolves in fats, it can pass easily through cell membranes. Together, this means that ethanol moves and works quickly in the body.
The breakdown of ethanol
The body contains powerful enzymes that are responsible for breaking down ethanol and for eliminating its by-products. As ethanol enters the stomach, it stimulates increased secretion of acid and also the enzyme alcohol dehydrogenase, which is the first line of attack in the breakdown process. This enzyme converts ethanol into an inactive form called acetaldehyde. While this molecule does not have the effects of ethanol, it can damage cells.
Therefore, to make sure that acetaldehyde is also eliminated from the body, a second enzyme takes over—aldehyde dehydrogenase—and turns acetaldehyde into an inactive and innocuous molecule called acetic acid.
Only some of the ethanol ingested is broken down in the stomach. Most of it passes into the small intestine and from there into the blood stream, which sends it on to the liver. The liver is the organ that breaks down most of the ethanol consumed. It is therefore also the organ that will take the largest toll from alcohol, especially from the toxic effects of acetaldehyde. This is the reason why people who drink heavily and over long periods of time often develop liver damage called cirrhosis.
Not all people have the same amounts of the two enzymes that break down ethanol. Women generally have less alcohol dehydrogenase in their stomachs, which, as it will be discussed later, makes them more susceptible to the effects of alcohol. Since it cannot be broken down as quickly, more ethanol passes into the blood and body, where it lingers longer than in men.
Some people, in particular Asians, often have a genetically different form of aldehyde dehydrogenase that is not active. This leads to the so-called "flushing reaction," where the person becomes hot and sweaty, dizzy, nauseous, and turns red in the face. In addition, many Asians also have an inactive form of alcohol dehydrogenase, the enzyme that produces the toxic breakdown product acetaldehyde. This makes such individuals much less able to eliminate the molecule from their bodies.
Ethanol (or ethyl alcohol) has the chemical ability to enter the bloodstream and various organs in the body very quickly. In fact, in the four or five seconds it takes for a mouthful of beer to reach the stomach, ethanol is already being absorbed by the gastro-intestinal tract (stomach and small intestine). From there, alcohol passes to the brain, where it acts on the neurochemical pathways that control many of your functions. The ethanol contained in beer, wine, and spirits has the same effect on the body.
The general effects of alcohol
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Alcohol (this term will be used to refer specifically to ethanol) acts on the brain as an anesthetic, sedative, and stimulant, depending on how much of it is consumed. The effects of alcohol change the more one drinks. Many people drink alcohol for these effects. However, it is important to know that drinking in excess can also be extremely harmful.
In relatively small amounts alcohol can:
- make one feel light-headed;
- produce sensations of dizziness;
- lower inhibitions and alter behavior;
- produce mood changes;
- increase the speed of the heart;
- dilate blood vessels in the skin, making the skin look red and flushed as more blood rises to the surface of the body;
- increase sweating, also related to the dilation of blood vessels;
- interfere with the ability of the brain to control body temperature;
- irritate the lining of the stomach;
- impair coordination and slur speech;
- increase the need to urinate.
Of course, there are also other consequences of these effects. For example, perhaps the most obvious primary effect of lowering inhibitions and altering behavior also makes people more friendly and extroverted. This (generally beneficial) effect of alcohol is why it is sometimes described as "a social lubricant."
There are also potentially negative effects, such as, for some people, increased bravado and a greater willingness to be sexually active. Some people who drink—even at relatively low levels—may become aggressive and even violent.
Drinking more heavily increases the sense of irritability, euphoria, and also makes control of movements and speech increasingly difficult. People who drink very heavily are likely to eventually pass out. If they have been drinking up to and beyond a certain point, they may fall into a coma. At extreme levels of drinking, people may even die of what is called acute alcohol poisoning.
Effects on men and women
It is important to understand that alcohol’s effects are different for men and women (see also MODULE 9: Women and Alcohol). In general, men are able to drink more alcohol before they feel its effects. This has to do with their larger body size, as well as with the fact that more of a woman’s body is made up of fat. As a result, since alcohol dissolves in fat, it reaches higher concentrations more quickly in the bodies of women than in those of men. It also has to do, as we have seen earlier, with the difference in enzymes that break down ethanol in the body and help eliminate it from the system.
This means that women may feel the primary effects of alcohol more quickly. For example, they may become tipsy sooner. It also means that it takes less alcohol for women who drink to harm their bodies than it takes men to do the same amount of harm.
There are also other factors that influence what effect alcohol will have on the body. Age makes a difference. Older people become more susceptible to the effects of alcohol because of their decreased ability to break it down. In addition, they are more likely to be in poor health and taking medications than their younger counterparts, making older individuals more sensitive to the effects of alcohol.
Young people are also more sensitive to alcohol, especially when it comes to harm (see MODULE 11: Young People and Alcohol). There are a number of reasons for this. For example, young people are generally inexperienced drinkers and are prone to taking more risks than adults. The physiology of young people and the developmental changes taking place within their brains and other organs also increase their risk for harm. Young people may not be fully aware of the effect that alcohol has on them and are generally less sensitive to the symptoms of intoxication. At the same time, alcohol and its by-products may have a greater harmful effect on their bodies.
How quickly alcohol acts also depends on whether an individual is eating while drinking or is drinking on an empty stomach. Food slows down the absorption of alcohol from the "gut" into the blood stream, slowing down its effects and slowing down intoxication. For that reason, it is generally recommended that drinking be accompanied with food.
Alcohol may interact with some medications. In some cases, such as with certain antibiotics, it may make them less effective. In other instances, alcohol may dangerously change the effects of certain medications, especially those that act on the central nervous system.
Alcohol is likely to have quite different effects on different individuals, and, for some people, not drinking at all may be advisable (see MODULE 8: "At-risk" Populations). This includes individuals who are unable to metabolize alcohol easily, people with a family history of alcohol dependence (or alcoholism), and individuals who have trouble controlling the amount they drink (see MODULE 17: Alcohol Dependence and Treatment). Pregnant women may also be at risk from drinking due to potential damage to the fetus, although the exact levels of drinking at which such damage begins to occur are not known (see MODULE 10: Drinking and Pregnancy).
What is "a drink"?
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In order to determine how much alcohol an individual has consumed, two pieces of information are needed: the volume contained in the glass or container used and information on how much of that volume is ethanol.
It is then possible to calculate the total amount of alcohol in each drink. It is useful to remember that the following contain approximately the same amount of alcohol:
1 small beer = 1 small glass of wine = 1 nip of spirits = 1 UNIT of ALCOHOL
In some countries, there is an official "standard" size for drinks (see MODULE 20: Standard Drinks). This standard is used to:
- allow servers in bars and restaurants to measure how much they are serving;
- allow customers to know what they are being served; and
- give advice to people on how much they are drinking and what the potential effects are likely to be on their health.
In most countries where the standard is defined, 10g of ethanol is considered to be a drink or unit. However, in the United States, for example, a standard drink contains 14g, while a U.K. standard unit contains 8g of ethanol.
Using these standard drinks as guides, some countries have issued official advice and guidelines regarding how much alcohol adult individuals can drink with little or no risk for harm to their health (see MODULE 19: Drinking Guidelines). We have already discussed the difference between men and women in how alcohol is metabolized in the body. Official drinking guidelines take these differences into account and most of them suggest that women drink less than men. Such recommendations are based on the best available scientific evidence about drinking levels and their effects on the human body. Where the exact recommendations are set varies between different countries.
It is generally accepted that the effect of alcohol, in both the long-and short-term, has more to do with how much alcohol is consumed and the way in which it is consumed, than whether it is in the form of beer, wine, or spirits.
The short-term effects of alcohol
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When alcohol is consumed, it quickly spreads through the body, where it has a range of short-term effects. These effects, in turn, have consequences for health, mental and physical functioning, and behavior. Such short-term effects are also caller the acute effects of alcohol.
Blood alcohol concentration
The first facet of short-term effects of alcohol is related to its immediate action within the body and how it is metabolized.
How much alcohol is in the blood stream is a good indicator of how much alcohol an individual has drunk. It is also often used for legal reasons as a measure of intoxication, for example, with regard to drinking and driving (MODULE 15: Drinking and Driving and MODULE 16: Blood Alcohol Concentration Limits).
How quickly blood alcohol concentration (BAC) levels increase differs from one person to another, depending on weight, gender, and on whether or not food accompanies drinking.
Alcohol in blood is measured in terms of weight per volume. The most commonly used measurements are grams of ethanol per deciliter of blood (g/dl=g/100ml), used in the United States, and milligrams of ethanol per milliliter of blood (mg/ml), used in much of Europe. For example, 0.05 g/dl = 0.5 mg/ml. Other metrics frequently used in policy and research are mg/dl (e.g., 50 mg/dl) or g/l (e.g., 0.5 g/l).
Table 1 below illustrates the acute effects of alcohol on a "typical" person. However, it must be recognized that different people react to alcohol differently, depending on their gender, size, weight, genetic makeup, state of health, and/or amount of food they have had to eat.
Table 1. BAC Levels and Their Effects for a Typical Person
BAC level (mg/ml)
0.2 – 0.9
mood changes, acting inappropriately, impaired coordination, slowed reaction time, diminished response to pain
1.0 – 1.9
lack of coordination, inability to correctly interpret what is happening, impaired judgment, difficulty in walking and standing steadily
2.0 – 2.9
3.0 – 3.9
serious intoxication, lowered body temperature, partial amnesia ("blackout") likely
alcohol poisoning, coma, risk of death (about 50% of people who have a BAC ≥ 4.00 will die of alcohol poisoning)
In very broad terms, one standard drink of wine, beer, or spirits raises BAC to approximately 0.2 mg/ml. While the metabolism of alcohol is different for men and women and depends on several other factors, this is a useful rule of thumb to gauge drinking. Of course, alcohol is being metabolized in the body almost as soon as it is consumed. However, this is not a very fast process. The speed at which the liver processes alcohol will vary from individual to individual. In general terms, a healthy liver will reduce BAC by about 0.15 mg/ml per hour.
Most countries have legislation around drinking and driving and the BAC levels above which driving becomes an offence (see MODULE 16: Blood Alcohol Concentration Limits). In some countries, no amount of alcohol in the blood is permissible, while in others, the limit is 0.2 mg/ml, or one drink. However, there are countries in which the levels are higher: 0.5 mg/ml or even 0.8–1.0 mg/ml.
Short-term effects of alcohol include the positive aspects of increased sociability and wellbeing. However, other possible harms may be associated with over-consumption: Accidents and injuries, including road traffic crashes, are frequently related to drinking.
Hangovers are a common short-term effect of drinking too much alcohol. Headaches, nausea, dry mouth, lethargy, and an increased sensitivity to light and sound are typical symptoms.
Much of the unpleasant sensation associated with hangovers is due to dehydration. Alcohol is a potent diuretic. It blocks the release of a hormone responsible for recycling water in the blood stream through the kidneys. This hormone is called anti-diuretic hormone (ADH). Water usually reabsorbed into the blood stream is now channeled out of the body to flush out the alcohol and its metabolites. The body needs water to break down alcohol, and it is important that water be replenished.
Dry mouth and headaches are a direct result of dehydration and changes in pressure within blood vessels. Fatigue, lethargy, and weakness that also accompany hangovers are the result of a build-up of lactic acid, which is normally cleared from the body through the liver. Lactic acid is familiar to all those who have had sore muscles from exercising. When high levels of alcohol are present in the body, the liver’s first priority is to eliminate it from the system, allowing other toxins (including lactic acid) to build up.
Alcohol also stimulates acid to be released into the stomach, as discussed earlier. The increased acid results in queasiness.
It is possible to prevent the symptoms of the hangover by drinking plenty of water and other non-alcoholic fluids after drinking. This will allow the body to regain its balance and more efficiently clear alcohol and its breakdown products from the system.
It is important to bear in mind that beer, wine, and distilled spirits all produce hangovers when too much of any of them is consumed.
The long-term effects of alcohol
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In addition to its short-term effects on the body and behavior, alcohol also has a number of long-term consequences. Such chronic effects of alcohol consumption can be both beneficial and harmful. In general, the benefits are related to moderate drinking over long periods of time, while the harms are mostly due to excessive or irresponsible consumption.
Research studies have documented that drinking moderately may have a protective effect on the heart and circulatory system. Especially for middle-aged men, alcohol may help with circulation and reduce the build-up of cholesterol along blood vessel walls, reducing the risk of heart attacks and certain types of stroke.
For women, especially older women, moderate drinking may help prevent the onset of osteoporosis, the weakening of the bones that often sets in at old age (see MODULE 9: Women and Alcohol). It has also been shown that moderate drinking can benefit some individuals with certain types of diabetes.
Due to its relaxing properties, alcohol contributes to general wellbeing and quality of life. Especially in older people, moderate drinking may make a difference in how they feel and enhance their awareness and sociability.
However, it is important to bear in mind that the effects of alcohol may be different from one individual to another.
The negative long-term effects of alcohol are mostly associated with heavy drinking over long periods of time. People who drink excessively have an increased risk of becoming alcohol-dependent. Heavy drinking may also result in brain damage and harm to the liver, as discussed above.
Despite the possible benefit to the heart from moderate drinking, heavy drinking—especially long-term heavy drinking—may actually damage the heart or increase blood pressure. Some people who drink heavily also develop certain types of cancers, in particular of the mouth and throat.
There is evidence that women who drink heavily during pregnancy are likely to cause serious damage to their unborn children, including mental retardation and physical defects (see MODULE 10: Drinking and Pregnancy). This damage is likely to persist throughout these children’s lives. Some official guidelines recommend that women refrain from drinking during pregnancy, except possibly negligible amounts
Young people’s drinking is another important area (MODULE 11: Young People and Alcohol). Due to changes in their physiology due to the process of maturation, young people are uniquely susceptible to alcohol-related harm. Heavy and irresponsible drinking may result in long-term effects on the brain, on bone maturation, and on the reproductive system.
While it is unclear whether those who start drinking early are more likely to have alcohol problems and become dependent later in life, there is evidence that heavy drinking among young people does make them more likely to suffer later harm.
Amount of alcohol consumed or drinking pattern?
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Traditional views about the effects of alcohol—especially the dangers of alcohol abuse—concentrate on the total amount of alcohol a person consumes. Conventionally, the total amounts consumed by all the people within a particular population (for example, in a single country) are added together and then divided by the number of people in that population. This gives an average amount of alcohol consumed per person, or average per capita consumption.
As we all know, not all of us drink in the same way. Some of us drink little and rarely, some drink every day, others may drink a lot, and still others nothing at all. It is therefore unlikely that we will all have the same effects as a result of our drinking. It is just as unrealistic to suggest that we should all change our drinking behavior in the same way.
It would be more useful, therefore to look at the way in which individuals drink—or their drinking patterns. Drinking patterns describe a range of facets of drinking behavior. Patterns of drinking are at least as important as levels of alcohol consumption in predicting whether people will experience problems with their drinking.
What do we mean by "patterns" of drinking? Patterns refer to several different aspects of drinking behavior. These include:
- when a person drinks (e.g., during meals, at special occasions or events, at the end of the work day);
- how often an individual drinks heavily and under what circumstances (e.g., to relieve stress, at parties or sporting events, on a daily basis);
- with whom people drink (e.g., with family around the dinner table, with friends in a restaurant or a bar, alone at home);
- what individuals are drinking (e.g., beer, wine, or spirits made according to safety and quality standards or "moonshine" that may be contaminated, see MODULE 21: Noncommercial Alcohol);
- the drinking culture (e.g., is drinking seen as acceptable behavior or something that is frowned upon, is there peer pressure to drink heavily?).
Some people drink heavily within a short period of time on certain occasions. This is typically called "binge" drinking (see MODULE 6: "Binge" Drinking). All in all, this is a negative drinking pattern, often associated with adverse health and social consequences.