Alcohol is a potent drug with a range of side effects. The amount and circumstances of consumption play a large part in determining the extent of intoxication, e.g. consuming alcohol after a heavy meal is less likely to produce visible signs of intoxication than consumption on an empty stomach. Hydration also plays a role, especially in determining the extent of hangovers.
Alcohol has a biphasic effect on the body, which is to say that its effects change over time. Initially, alcohol generally produces feelings of relaxation and cheerfulness, but further consumption can lead to blurred vision and coordination problems. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every tissue of the body. After excessive drinking, unconsciousness can occur and extreme levels of consumption (when the concentration of alcohol in the bloodstream is over 0.5 percent) can lead to alcohol poisoning and death. Death can also be caused by asphyxiation if vomit, a frequent result of overconsumption, blocks the trachea and the individual is too inebriated to help themselves. An appropriate first aid response to an unconscious, drunken person is to place them in the recovery position.
Intoxication frequently leads to a lowering of one's inhibitions, and intoxicated people will do things they would not do while sober, ranging from the mildly socially awkward to the downright embarrassing to the actually illegal. The term intoxication is typically used in legal proceedings when some crime has been committed during a state of inebriation.
Contents
- 1 Intoxication
- 2 Action on the brain
- 3 Carcinogenic effects
- 4 Metabolism of alcohol and action on the liver
- 5 Dehydration
- 6 Hangover
- 7 Beneficial effects of alcohol
- 8 Effects by dose
- 8.1 Moderate doses
- 8.2 Excessive doses
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Intoxication
In small amounts, ethanol causes a mild euphoria and removes inhibitions. In large doses, ethanol acts as a central nervous system depressant and causes drunkenness, generally at a blood ethanol content of about 0.1%. At higher contents, alcohol causes intoxication, coma and death. A blood ethanol content above 0.4% can be fatal, although regular heavy drinkers can tolerate somewhat higher levels than non-drinkers. Eight to ten drinks per hour is considered a fatal dosage for the average 54 kg (119 lb.) person. One drink is equivalent to one shot of 40% abv (80 proof) liquor, one 12 US fl oz (355 ml) beer, or one 4–5 US fl oz (120–150 ml) glass of wine.
In the UK, a "unit" of alcohol is 10 ml pure ethanol; so examples of drinks containing one unit of alcohol include one 25 ml measure of spirits (40% ABV), one 125 ml glass of wine (8% ABV), one half-pint (284 ml) of weak (3.5% ABV) beer, or just over one third of a pint (about 200 ml) of "premium" (5% ABV) lager. (Note that in fact many wines are about 12% ABV, so would contain 1.5 units per 125 ml glass, and that many establishmens serve wine by the 175 ml glass. A 175ml glass of 12% wine contains 2.1 units of alcohol).
To determine how many units an alcoholic drink contains a simple formula may be used:
(ABV*ml)/1000
Thus a "shot" of 40% ABV liquor in the US (which is ~44ml or 1.5 US fl oz) is actually 1.76 units of alcohol. ((40*44)/1000) Unfortunately, in the US, most still have the misconception that one US shot is 1 unit when in fact it is almost double that; which can lead to health problems and more drunken driving.
Highest recorded non-lethal level of blood alcohol is 0.914 mg/dl.
Alcoholism, the dependency on alcohol, is a major public health problem. Alcoholics develop a number of health problems, with cirrhosis of the liver among the most significant. Unlike withdrawal from other drug/intoxicants, withdrawal from heavy alcohol consumption can be fatal and is known as delirium tremens.
Excessive alcohol consumption during pregnancy carries a heavy risk of causing a series of permanent mental and physical defects in the child, known as fetal alcohol syndrome.
Action on the brain
Ethanol is quickly absorbed into the bloodstream and reaches the brain. As a small molecule, it is able to cross the blood-brain barrier. The euphoric effects of ethanol are probably due to its causing the release of endorphins, the body's natural response to pleasurable activity.
The CNS depressant effect likely is due to ethanol's acting on the BK channels.[1] A BK channel is a calcium dependent potassium channel. It has been known to act on GABA receptors, but this is probably just a secondary effect from activation of the BK channels. Its effect on GABA receptors is probably similar to the action of benzodiazepines such as diazepam. GABA is an inhibitory neurotransmitter, meaning it acts to slow down or inhibit nerve impulses. Ethanol increases the effectiveness of GABA acting through GABAA receptors. When used over a long time, ethanol changes the number and type of GABA receptors, and this is thought to be the cause of the violent withdrawal effects of alcoholics.
Ethanol also interferes with synaptic firing and causes the death of brain cells. This cell death is caused by an increased concentration of intracellular calcium which has several effects. It weakens the electrochemical gradient across the cell membranes. It is this gradient which is the motive force of membrane pumps and channels (cells, especially neurons, quickly die without proper membrane pump and channel function). Calcium also activates proteases that cause degradation of cell proteins.
There is also direct damage to cell membranes from free-radicals that are produced from alcohol metabolism.
Carcinogenic effects
Small amounts of alcohol do not act as a carcinogen. However, many studies have shown that large amounts of alcohol greatly increase the risk of developing a cancer. The strongest link between alcohol and cancer involves cancers of the upper digestive tract, including the esophagus, the mouth, the pharynx, and the larynx. Less consistent data link alcohol consumption and cancers of the liver, breast, and colon.
Upper digestive tract. Chronic heavy drinkers have a higher incidence of esophageal cancer than does the general population. The risk appears to increase as alcohol consumption increases. An estimated 75 percent of esophageal cancers in the United States are attributable to chronic, excessive alcohol consumption.
Nearly 50 percent of cancers of the mouth, pharynx, and larynx are associated with heavy drinking. According to mid-1980s U.S. case-control study, people who consumed an average of more than four drinks per day incurred a nine-fold increase in risk of oral and pharyngeal cancer, while there was about a four-fold increase in risk associated with smoking two or more packs of cigarettes per day. Heavy drinkers who also were heavy smokers experienced a greater than 36-fold excess compared to abstainers from both products.
Liver. Prolonged, heavy drinking has been associated in many cases with primary liver cancer. However, it is liver cirrhosis, whether caused by alcohol or another factor, that is thought to induce the cancer. In areas of Africa and Asia, liver cancer afflicts 50 or more people per 100,000 per year, usually associated with cirrhosis caused by hepatitis viruses. In the United States, liver cancer is relatively uncommon, afflicting approximately 2 people per 100,000, but excessive alcohol consumption is linked to as many as 36 percent of these cases by some investigators.
For further information, see Alcohol and cancer
Metabolism of alcohol and action on the liver
The liver contains a special enzyme (alcohol dehydrogenase) that breaks down alcohols into acetaldehyde, which is turned into acetic acid by the enzyme acetaldehyde dehydrogenase, and then yet another enzyme converts the acetate into fats or carbon dioxide and water. The fats are mostly deposited locally which leads to the characteristic "beer belly". Chronic drinkers, however, so tax this metabolic pathway that things go awry: fatty acids build up as plaques in the capillaries around liver cells and those cells begin to die, which leads to the liver disease cirrhosis. The liver is part of the body's filtration system and if it is damaged then certain toxins build up thus leading to symptoms of jaundice.
The alcohol dehydrogenase of women is less effective than that of men. Combined with the lower amount of water in women's bodies, this means that women typically become drunk earlier than men.
Some people, especially those of East Asian descent, have a genetic mutation in their acetaldehyde dehydrogenase gene, resulting in less potent acetaldehyde dehydrogenase. This leads to a buildup of acetaldehyde after alcohol consumption, causing hangover-like symptoms such as flushing, nausea, and dizziness. These people are unable to drink much alcohol before feeling sick, and are therefore less susceptible to alcoholism. [2], [3] This adverse reaction can be artificially reproduced by drugs such as disulfiram, which are used to treat chronic alcoholism by inducing an acute sensitivity to alcohol.
Dehydration
Consumption of ethanol has a rapid diuretic effect, meaning that more urine than usual is produced, since ethanol inhibits the production of antidiuretic hormone.
Overconsumption can therefore lead to dehydration (the loss of water). It is difficult to replenish the body's fluids using only alcoholic beverages. As large amounts of alcohol are consumed, the diuretic effect causes the body to lose more water than is contained in the beverage.
Hangover
- Main article: Hangover
A common after-effect of ethanol intoxication is the unpleasant sensation known as hangover, which is partly due to the dehydrating effect of ethanol. Hangover symptoms include dry mouth, headache, nausea, and sensitivity to light and noise. These symptoms are partly due to the toxic acetaldehyde produced from alcohol by alcohol dehydrogenase, and partly due to general dehydration. The dehydration portion of the hangover effect can be mitigated by drinking plenty of water between and after alcoholic drinks. Other components of the hangover are thought to come from the various other chemicals in an alcoholic drink, such as the tannins in red wine, and the results of various metabolic processes of alcohol in the body, but few scientific studies have attempted to verify this. Consuming a large amount of water is the best way to overcome a hangover.
Beneficial effects of alcohol
Several studies have shown that regular consumption of moderate amounts of alcohol lowers the incidence of coronary heart disease and raises the level of high density lipoprotein cholesterol ("good cholesterol"). See Alcohol consumption and health.
Effects by dose
Moderate doses
Although alcohol is commonly thought of purely as a depressant, at low concentrations it can actually stimulate certain areas of the brain. Alcohol sensitises the N-methyl-D-aspartate (NMDA) system of the brain, making it more receptive to the neurotransmitter glutamate. Stimulated areas include the cortex, hippocampus and nucleus accumbens, which are responsible for thinking and pleasure seeking. Another one of alcohol's agreeable effects is body relaxation, possibly caused by heightened alpha brain waves surging across the brain. Alpha waves are observed (with the aid of EEGs) when the body is relaxed. Heightened pulses are thought to correspond to higher levels of enjoyment.
A well-known side effect of alcohol is lowering inhibitions. Areas of the brain responsible for planning and motor learning are dulled. A related effect, caused by even low levels of alcohol, is the tendency for people to become more animated in speech and movement. This is due to increased metabolism in areas of the brain associated with movement, such as the nigrostriatal pathway. This causes reward systems in the brain to become more active, and combined with released inhibition can induce people to behave in an uncharacteristically loud and cheerful manner.
Behavioural changes associated with drunkenness are, to some degree, contextual. A scientific study found that people drinking in a social setting significantly and dramatically altered their behaviour immediately after the first sip of alcohol, well before the chemical itself could have filtered through to the nervous system. Likewise, people consuming non-alcoholic drinks often exhibit drunk-like behavior on a par with their alcohol-drinking companions even though their own drinks contained no alcohol whatsoever.
Excessive doses
The effect alcohol has on the NMDA receptors, earlier responsible for pleasurable stimulation, turns from a blessing to a curse if too much alcohol is consumed. NMDA receptors start to become unresponsive, slowing thought in the areas of the brain they are responsible for. Contributing to this effect is the activity which alcohol induces in the gamma-aminobutyric acid system (GABA). The GABA system is known to inhibit activity in the brain. GABA could also be responsible for the memory impairment that many people experience. It has been asserted that GABA signals interfere with the registration and consolidation stages of memory formation. As the GABA system is found in the hippocampus, (among other areas in the CNS), which is thought to play a large role in memory formation, this is thought to be possible.
Blurred vision is another common symptom of drunkenness. Alcohol seems to suppress the metabolism of glucose in the brain. The occipital lobe, the part of the brain responsible for receiving visual inputs, has been found to become especially impaired, consuming 29 percent less glucose than it should. With less glucose metabolism, it is thought that the cells aren't able to process images properly.
Often, after much alcohol has been consumed, it is possible to experience vertigo, the sense that the room is spinning. This is associated with abnormal eye movements called nystagmus, specificially positional alcohol nystagmus. In this case, alcohol has affected the organs responsible for balance (vestibular system), present in the ears. Balance in the body is monitored principally by two systems: the semicircular canals, and the utricle and saccule pair. Inside both of these is a flexible blob called a cupula, which moves when the body moves. This brushes against hairs in the ear, creating nerve impulses that travel through the vestibulocochlear nerve (Cranial nerve VIII) in to the brain. However, when alcohol gets in to the bloodstream it distorts the shape of the cupola, causing it to keep pressing on to the hairs. The abnormal nerve impulses tell the brain that the body is rotating, causing disorientation and making the eyes spin round to compensate. When this wears off (usually taking until the following morning) the brain has adjusted to the spinning, and interprets not spinning as spinning in the opposite direction causing further disorientation. This is often a common symptom of the hangover.
Another classic finding of alcohol intoxication is ataxia, in its appendicular, gait, and truncal forms. Appendicular ataxia results in jerky, uncoordinated movements of the limbs, as though each muscle were working independently from the others. Truncal ataxia results in postural instability; gait instability is manifested as a disorderly, wide-based gait with inconsistent foot positioning. Ataxia is responsible for the observation that drunk people are clumsy, sway back and forth, and often fall down. It is probably due to alcohol's effect on the cerebellum.
Extreme over-indulgence can lead to alcohol poisoning and death due to respiratory depression.
A rare complication of acute alcohol ingestion is Wernicke encephalopathy, a disorder of thiamine metabolism. If not treated with thiamine, Wernicke encephalopathy can progress to Korsakoff psychosis, which is irreversible.
Chronic alcohol ingestion over many years can produce atrophy of the vermis, which is the part of the cerebellum responsible for coordinating gait; vermian atrophy produces the classic gait findings of alcohol intoxication even when its victim is not inebriated.
Severe drunkenness and diabetic coma can be mistaken for each other on casual inspection, with potentially serious medical consequences for diabetics. The major physical finding they share is the sickly-sweet odor of ketosis on the breath; alcoholic ketosis and diabetic ketosis are both marked by the presence of acetone and other ketones in the bloodstream, although the ketones are produced by different metabolic pathways in each disorder. Measurement of the serum glucose and ethanol concentrations in comatose individuals is routinely performed in the emergency department and easily distinguishes the two conditions.
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