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Effects of Alcohol on the Body
Alcohol, specifically ethanol, is a potent psychoactive 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. The concentration of alcohol in blood is usually given by BAC.
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 can lead to alcohol poisoning and death (a concentration in the blood stream of 0.55% will kill half the population). Death can also be caused by asphyxiation of vomit, a frequent result of overconsumption, blocks the trachea and the individual is too inebriated to respond. 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, often ignoring social, moral, and legal considerations. The term intoxication is typically used in legal proceedings when some crime has been committed during a state of inebriation.
Ethanol acts as a central nervous system depressant. In small amounts, ethanol causes a mild euphoria and removes inhibitions, and in large doses it causes drunkenness, generally at a blood ethanol content of about 0.1%. At higher concentrations, 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 establishments 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 (approximately 44ml vs. 1.5 US fl oz) is actually 1.76 units of alcohol. ((40*44)/1000) As a result, one U.S. "shot" of alcohol is almost double the amount experienced by the international community. As a result, "shot-takers" in the United States should be aware of the differences between the two standards and adjust accordingly to prevent alcohol overconsumption. The highest recorded non-lethal level of blood alcohol is 0.914 mg/dl.
Alcoholism, addiction to 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 some other drugs/intoxicants such as the opioids, withdrawal from heavy alcohol consumption can produce delirium tremens that can be fatal.
Excessive alcohol consumption during pregnancy carries a heavy risk 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. For reasons that are still being studied, it then triggers the release of dopamine and endorphins into the bloodstream, which cause euphoria.
The CNS depressant effect likely is due to ethanol's acting on the BK channels. A BK channel is a calcium dependent potassium channel. Ethanol potentiates the activity of BK channels, which reduces the excitability of the neuron.  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 the alcohol metabolism.
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 % of esophageal cancers in the United States are attributable to chronic, excessive alcohol consumption.
Nearly 50 % 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.
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 % of these cases by some investigators.
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. 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.
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.
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. Dehydration causes the brain to shrink away from the skull slightly. This triggers pain sensors on the outer surface of the brain which causes the headache. 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 prevent and lessen the effects of a hangover.
Beneficial Effects of Alcohol
Several studies have shown that regular consumption of moderate amounts of alcohol (ie below recommended daily limits from US or UK sources) can lower the incidence of coronary heart disease and raise the level of high density lipoprotein cholesterol ("good cholesterol").
Moderate drinkers tend to have better health and live longer than those who are either abstainers or heavy drinkers. In addition to having fewer heart attacks and strokes, moderate consumers of alcoholic beverages (beer, wine or distilled spirits or liquor) are generally less likely to suffer hypertension or high blood pressure, peripheral artery disease, Alzheimer's disease and the common cold. Sensible drinking also appears to be beneficial in reducing or preventing diabetes, rheumatoid arthritis, bone fractures and osteoporosis, kidney stones, digestive ailments, stress and depression, poor cognition and memory, Parkinson's disease, hepatitis A, pancreatic cancer, macular degeneration (a major cause of blindness), angina pectoris, duodenal ulcer, erectile dysfunction, hearing loss, gallstones, liver disease and poor physical condition in elderly.
Alcohol Consumption and Health
The relationship between alcohol consumption and health has been the subject of formal scientific research since at least 1926, when Dr. Raymond Pearl published his book, Alcohol and Longevity asserting that drinking alcohol in moderation is associated with greater longevity than either abstaining or drinking heavily. Subsequently, various studies have examined the health effects of different degrees of alcoholic beverage consumption; while it is widely recognized that heavy or abusive drinking has health hazards, including cell and organ damage in the brain, liver, and kidneys, and the immune system, "moderate consumption," frequently defined as the consumption of 1-3 alcoholic drinks daily (depending on the age and gender of the subjects) has been hypothesized to have a positive effect on longevity.
A large number of independent peer-reviewed studies in modern medical literature support the hypothesis that moderate alcohol consumption can be associated with benefits in longevity and reductions in coronary heart disease, stroke, and other diseases. Proposed mechanisms of these benefits include the effect of alcohol on cholesterol levels, insulin activity, blood pressure, and the chemistry of blood clotting. Frequently, such studies qualify these findings with admonitions against heavy alcohol consumption or abuse, due to the negative health effects known to be associated with this behavior.
Alcohol Consumption and Longevity
Doll et al. (2005) published the results of a 23-year prospective study of 12,000 male British physicians aged 48-78, finding that overall mortality was significantly lower in the group consuming an average of 2-3 "units" (standard alcoholic drinks) per day than in the non-alcohol-drinking group (relative risk 0.81, confidence interval 0.76-0.87, P = 0.001). The authors noted that the causes of death that are already known to be augmentable by alcohol accounted for only 5% of the deaths (1% liver disease, 2% cancer of the mouth, pharynx, larynx, or oesophagus, and 2% external causes of death) and were significantly elevated only among men consuming >2 units/day.
In a 1996 American Heart Association scientific statement, Thomas A. Pearson, MD, Ph.D noted, "A large number of observational studies have consistently demonstrated a J-shaped relation between alcohol consumption and total mortality. This relation appears to hold in men and women who are middle aged or older. The lowest mortality occurs in those who consume one or two drinks per day.10 In teetotalers or occasional drinkers, the rates are higher than in those consuming one or two drinks per day. In persons who consume three or more drinks per day, total mortality climbs rapidly with increasing numbers of drinks per day."
Alcohol Consumption and Heart Disease
In the above-noted AHA statment, Pearson reviewed the evidence supporting the effect of alcohol consumption on coronary heart disease (CHD): "More than a dozen prospective studies have demonstrated a consistent, strong, dose-response relation between increasing alcohol consumption and decreasing incidence of CHD. The data are similar in men and women in a number of different geographic and ethnic groups. Consumption of one or two drinks per day is associated with a reduction in risk of approximately 30% to 50%. Studies of coronary narrowings defined by cardiac catheterization or autopsy show a reduction in atherosclerosis in persons who consume moderate amounts of alcohol. In general, the inverse association is independent of potential confounders, such as diet and cigarette smoking. Concerns that the association could be an artifact due to cessation of alcohol consumption in persons who already have CHD have largely been disproved."
Alcohol Consumption and Stroke
Berger et al.,(1999) in a study of over 22,000 male physicians aged 40-84 years old over an average of 12 years, found that "light-to-moderate alcohol consumption" reduces the overall risk of stroke and the risk of ischemic stroke in men, with a benefit apparent with as little as one drink per week, and no greater effect seen at greater consumption of up to to one drink per day.
A 2003 meta-analysis by Reynolds et al. of 35 previous studies of the effect of alcohol consumption on stroke risk found that "compared with abstainers, consumption of more than 60 g of alcohol per day was associated with an increased relative risk of total stroke, 1.64 (95% confidence interval [CI], 1.39-1.93); ischemic stroke, 1.69 (95% CI, 1.34-2.15); and hemorrhagic stroke, 2.18 (95% CI, 1.48-3.20), while consumption of less than 12 g/d was associated with a reduced relative risk of total stroke, 0.83 (95%, CI, 0.75-0.91) and ischemic stroke, 0.80 (95% CI, 0.67-0.96), and consumption of 12 to 24 g/d was associated with a reduced relative risk of ischemic stroke, 0.72 (95%, CI, 0.57-0.91). The meta-regression analysis revealed a significant nonlinear relationship between alcohol consumption and total and ischemic stroke and a linear relationship between alcohol consumption and hemorrhagic stroke." (emphasis added)
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Health Effect and Type of Alcohol Consumed
In "Review of moderate alcohol consumption and reduced risk of coronary heart disease: is the effect due to beer, wine, or spirits?" (BMJ 1996;312:731-736 (23 March)) Eric B. Rimm et al. concluded that "results from observational studies where alcohol consumption can be linked directly to an individual's risk of coronary heart disease, provide strong evidence that all alcoholic drinks are linked with lower risk. Thus, a substantial portion of the benefit is from alcohol rather than other components of each type of drink."
The Director of the National Institute on Alcohol Abuse and Alcoholism has written that "numerous well-designed studies have concluded that moderate drinking is associated with improved cardiovascular health,"  and the Nutrition Committee of the American Heart Association reports that "the lowest mortality occurs in those who consume one or two drinks per day." 
The World Health Organization Technical Committee on Cardiovascular Disease asserted that the relationship between moderate alcohol consumption and reduced death from heart disease could no longer be doubted. (Wilkie, S. Global overview of drinking recommendations and guidelines. AIM Digest, Supplement, June 1997, 2-4, p. 4)
The U.S. National Institute on Alcohol Abuse and Alcoholism (NIAAA) has completed an extensive review of current scientific knowledge about the health effects of moderate alcohol consumption. It found that the lowest death rate from all causes occurs at the level of one to two drinks per day. That is, moderate drinkers have the greatest longevity.
The medical studies establishing this relationship are large (some include over 200,000 people), cross-cultural (have been conducted in countries around the world), and are sometimes long-term (the longest beginning in 1948 and continuing to this day).
To test the hypothesis that the results may reflect the poor health of alcoholics who now abstain, some studies have restricted the abstainers studied to lifelong teetotalers. Others have controlled for lifestyle factors, income levels, educational levels and other factors. The results have remained the same: Moderate drinkers tend to live longer than abstainers or heavy drinkers.
Source: Wikipedia - Effects of Alcohol on the Body & Alcohol Consumption and Health
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