Short-term effects of alcohol

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The short-term effects of alcohol on the human body can take several forms.

Alcohol, specifically ethanol, is a potent central nervous system depressant, with a range of side effects. The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, consuming alcohol after a heavy meal causes alcohol to absorb more slowly.^[1] Hydration also plays a role, especially in determining the extent of hangovers.^[2] The concentration of alcohol in blood is usually measured in terms of the blood alcohol content.

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 biological 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 0.40% will kill half of those affected^[3][4]). Death can also occur through asphyxiation by vomit. An appropriate first aid response to an unconscious, drunken person is to place them in the recovery position.

Signs and symptoms

Alcohol is a highly-abused substance that greatly exacerbates sleep problems. During abstinence, residual disruptions in sleep maintenance and sleep architecture are the greatest predictors of relapse. ^[5]

Moderate alcohol consumption and sleep disruptions

Moderate alcohol consumption 30-60 minutes before bedtime catalyzes disruptions in sleep maintenance and sleep architecture that are mediated by blood alcohol levels ^[6]. Disruptions in sleep maintenance are most marked once alcohol has been completely metabolized from the body. Under conditions of moderate alcohol consumption where blood alcohol levels average 0.06-0.08 percent and decrease 0.01-0.02 percent per hour, an alcohol clearance rate of 4-5 hours would coincide with disruptions in sleep maintenance in the second half of an 8 hr sleep episode ^[7]. In terms of sleep architecture, moderate doses of alcohol facilitate "rebounds" in rapid eye movement (REM) and stage 1 sleep; following suppression in REM and stage 1 sleep in the first half of an 8 hr sleep episode, REM and stage 1 sleep increase well beyond baseline in the second half. Moderate doses of alcohol also increase slow wave sleep (SWS) in the first half of an 8 hr sleep episode ^[8]. Enhancements in REM sleep and SWS following moderate alcohol consumption are mediated by reductions in glutamatergic activity by adenosine in the central nervous system ^[9]. In addition, tolerance to changes in sleep maintenance and sleep architecture develops within 3 days of alcohol consumption before bedtime ^[10].

Alcohol consumption and sleep improvements

Low doses of alcohol (one 12 oz. beer) are sleep-promoting by increasing total sleep time and reducing awakenings during the night. The sleep-promoting benefits of alcohol dissipate at moderate and higher doses of alcohol (two 12 oz beers and three 12 oz. beers, respectively) ^[11] . Previous experience with alcohol also determines whether or not alcohol is a "sleep promoter" or "sleep disrupter." Under free-choice conditions, in which subjects chose between drinking alcohol or water, inexperienced drinkers were sedated while experienced drinkers were stimulated following alcohol consumption ^[12]. In insomniacs, moderate doses of alcohol improve sleep maintenance ^[13].

Alcohol consumption and fatigue

Sleepiness influences the severity of alcohol consumption. Conditions of sleep deprivation encourage more episodes of alcohol consumption ^[14]. Increased alcohol consumption during the winter months for Northern climate residents is attributed to escalations in fatigue ^[15].

Alcohol abstinence and sleep disruptions

Sleep and hormonal disruptions following withdrawal from chronic alcohol consumption are the greatest predictors of relapse ^[16]. During abstinence, recovering alcoholics have attenuated melatonin secretion in the beginning of a sleep episode, resulting in prolonged sleep latencies ^[17]. Escalations in cortisol and core body temperatures during the sleep period contribute to poor sleep maintenance ^[18][19].

Effect by dosage

Different concentrations of alcohol in the human body have different effects on the subject.

The following lists the effects of alcohol on the body, depending on the blood alcohol concentration or BAC. Remember that tolerance varies considerably between individuals.

Please note: the BAC percentages provided below are just estimates and used for illustrative purposes only. They are not meant to be an exhaustive reference; please refer to a healthcare professional if more information is needed.

Euphoria (BAC = 0.03 to 0.12%).

• Subject may experience an overall improvement in mood and possible euphoria.
• They may become more self-confident or daring; they may become more friendly or talkative, and/or social.
• Their attention span shortens. They may look flushed.
• Their judgment is not as good—they may express the first thought that comes to mind, rather than an appropriate comment for the given situation. See: in vino veritas
• They may have trouble with fine movements, such as writing or signing their name.

Lethargy (BAC = 0.09 to 0.25%)

• Subject may become sleepy.
• They have trouble understanding or remembering things, even recent events. They do not react to situations as quickly.
• Their body movements are uncoordinated; they begin to lose their balance easily, stumbling; walking is not stable.
• Their vision becomes blurry. They may have trouble sensing things (hearing, tasting, feeling, etc.).

Confusion (BAC = 0.18 to 0.30%)

• Profound confusion—uncertain where they are or what they are doing. Dizziness and staggering occur.
• Heightened emotional state—aggressive, withdrawn, or overly affectionate. Vision, speech, and awareness are impaired.
• Poor coordination and pain response. Nausea and vomiting sometimes occurs.

Stupor (BAC = 0.25 to 0.40%)

• Movement severely impaired; lapses in and out of consciousness.
• Subjects can slip into a coma; will become completely unaware of surroundings, time passage, and actions.
• Risk of death is very high due to alcohol poisoning and/or pulmonary aspiration of vomit while unconscious.
• Loss of bodily functions can begin, including bladder control, breathing, heart rate.

Coma (BAC = 0.35 to 0.50%)

• Unconsciousness sets in.
• Reflexes are depressed (i.e., pupils do not respond appropriately to changes in light).
• Breathing is slower and more shallow. Heart rate drops. Death usually occurs at levels in this range.

Moderate doses

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French wines.

Ethanol inhibits the ability of glutamate to open the cation channel associated with the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. Alcohol sensitizes the N-methyl-D-aspartate (NMDAi) system of the brain, making it more receptive to the neurotransmitter glutamate^{[citation needed]}. 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 neurons transmitting electrical signals in an alpha waves-pattern; Alpha waves are observed (with the aid of EEGs) when the body is relaxed.

Alcohol has also been linked with lowered inhibitions, though it is unclear to what degree this is chemical versus psychological as studies with placebos can often duplicate the social effects of alcohol at low to moderate doses. Some studies have suggested that intoxicated people have much greater control over their behavior than is generally recognized, though they have a reduced ability to evaluate the consequences of their behavior.^[20] Behavioral changes associated with drunkenness are, to some degree, contextual^{[citation needed]}. A scientific study found that people drinking in a social setting significantly and dramatically altered their behavior immediately after the first sip of alcohol^{[citation needed]}, well before the chemical itself could have filtered through to the nervous system.

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 reduced understanding of the consequences of their behavior, can induce people to behave in an uncharacteristically loud and cheerful manner.

Alcohol has been known to mitigate the production of ADH (antidiuretic hormone), which is a hormone that acts on the kidney, favoring water reabsorption in the kidneys during filtration. This occurs because alcohol confuses osmoreceptors in the hypothalamus, which relay osmotic pressure information to the posterior pituitary, the site of ADH release. Alcohol makes the osmoreceptors signal as if there was a too low osmotic pressure in the blood, which triggers an inhibition of ADH. Consequently, one's kidneys are no longer able to reabsorb as much water as they should be absorbing, leading to creation of excessive volumes of urine and subsequently overall dehydration.

Excessive doses

Excessive doses are generally volumes that cause short- or long-term health effects.

NMDA receptors start to become unresponsive, slowing 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.

Anterograde amnesia, colloquially referred to as "blacking out", is another symptom of heavy drinking. This is the loss of memory since the episode of drinking.

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.

Pathophysiology

At low or moderate doses, alcohol primarily acts as a positive allosteric modulator of GABA_A. Alcohol binds to several different subtypes of GABA_A, but not to others. The main subtypes responsible for the subjective effects of alcohol are the α1β3γ2, α5β3γ2, α4β3δ and α6β3δ subtypes, although other subtypes such as α2β3γ2 and α3β3γ2 are also affected. Activation of these receptors causes most of the effects of alcohol such as relaxation and relief from anxiety, sedation, ataxia and increase in appetite and lowering of inhibitions which can cause a tendency towards violence in some people.^{[21][22][23][24][25][26][27]}

At higher dose ranges, other targets also become important. Alcohol at high doses acts as an antagonist of the NMDA receptor, and since the NMDA receptor is involved in learning and memory, this action is thought to be responsible for the "memory blanks" that can occur at extremely high doses of alcohol. People with a family history of alcoholism may exhibit genetic differences in the response of their NMDA glutamate receptors as well as the ratios of GABA-A subtypes in their brain. Alteration of NMDA receptor numbers in chronic alcoholics is likely to be responsible for some of the symptoms seen in delirium tremens during severe alcohol withdrawal, such as delirium and hallucinations. Other targets such as sodium channels can also be affected by high doses of alcohol, and alteration in the numbers of these channels in chronic alcoholics is likely to be responsible for the convulsions that can occur in acute alcohol withdrawal, as well as other effects such as cardiac arrhythmia. Also chronic NMDA receptor blockade may produce apoptosis in neurons which is likely to be one of the factors involved in producing the brain damage seen in long-term alcoholic patients. Other targets that are affected by alcohol include cannabinoid, opioid and dopamine receptors, although it is unclear whether alcohol affects these directly or if they are affected by downstream consequences of the GABA/NMDA effects.^{[28][29][30][31][32][33][34][35]}

Epidemiology

Disability-adjusted life year for alcohol use disorders per 100,000 inhabitants in 2002.

     no data      less than 50      50-150      150-250      250-350      350-450      450-550      550-650      650-750      750-850      850-950      950-1050      more than 1050

Research

Animal models using mammals and invertebrates have been informative in studying the effects of ethanol on not only pharmacokinetics of alcohol, but also in pharmacodynamics, particularly in the nervous system. Ethanol-induced intoxication is not uncommon in the animal kingdom, as noted here:

More recently, studies using animal models have begun to elucidate the effects of ethanol on the nervous system. Traditionally, many studies have been performed in mammals, such as mice, rats, and non-human primates. However, non-mammalian animal models have also been employed; in particular, Ulrike Heberlein group at UC San Francisco has used the fruit fly, Drosophila melanogaster, taking advantage of its facile genetics to dissect the neural circuits and molecular pathways, upon which ethanol acts. The series of studies carried in the Heberlein lab has identified insulin and its related signaling pathways as well as biogenic amines in the invertebrate nervous system as being important in alcohol tolerance. ^[37][38][39] The value of antabuse (disulfiram) as a treatment for alcoholism has been tested using another invertebrate animal model, the honey bees.^[40] Importantly, some of the analogous biochemical pathways and neural systems have been known to be important in alcohol's effects on humans, while the possibility that others may also be important remains unknown. Research of alcohol's effects on the nervous system remains a hot topic of research, as scientists inch toward understanding the problem of alcohol addiction.

In addition to the studies carried out in invertebrates, researchers have also used vertebrate animal models to study various effects of ethanol on behaviors. Of note are studies carried out by the Myers group in University of Minnesota, who used the zebrafish model to study ethanol-induced teratogenesis and gametogenesis.^[41]

See also

• Blackout (alcohol-related amnesia)
• The spins, a state of dizziness and disorientation due to intoxication
• Acute alcohol intoxication

References

External links

• Global Status Report on Alcohol 2004 by the World Health Organization.
• Molecular Genetic Analysis of Ethanol Intoxication in Drosophila melanogaster, Ulrike Heberlein, Fred W. Wolf, Adrian Rothenfluh and Douglas J. Guarnieri, Integrative and Comparative Biology 2004 44(4):269-
• Jane behaving badly (New Scientist article on short-term effects of alcohol)

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