Factors of Intoxication: What Influences Your BAC, Ability To Drive
Alcohol effects everyone differently, and often times effects individuals differently depending on the conditions of their drinking. Clearly, many factors play a role in how drunk one gets, and what their BAC may be after a round of drinks. This article will attempt to explain many of the factors, and hopefully help you understand why things are the way they are.
Alcohol Absorption Into The Body
Alcohol is a complex substance, absorbed from all parts of the GI tract by simple diffusion into the blood. If food is present in the stomach, the alcohol will be absorbed primarily by the intestines rather than the stomache, resulting in a lower and delayed BAC peak. The larger the meal and the closer in time between eating and drinking, the lower the peak BAC - studies have shown that anywhere from a 9% to 23% reduction over drinking alone. The type of food has not been shown to have any measurable influence.
Drink strength has also been shown to affect absorption, with drinks below 10% and 30% being absorbed most rapidly. Drinks less than 10% are less concentrated and more difficult to absorb due to literal volume of alcohol, while drinks over 30% tend to irritate the GI tract linings, causing increased mucous and delayed absorption. As was the case with food, the delayed absorption will cause a later peak, though in this scenario, the increased drink strength will not cause a small peak BAC, but will just push it back in time.
Distribution Throughout The Body
Alcohol is carried through the body in the blood, with an equilibrium eventually being reached such that all points in the system contain an approximately equal concentration of alcohol. The concentration differs, though based on a number of factors. Because alcohol has a high affinity for water, it tends to accumulate in body tissues and fluids in proportions related to the amount of water they contain. In the human body, this is generally proportional to body fat. In general, a person with low percentage of body fat will have a lower BAC than a person with a higher percentage body fat.
In general, women tend to have a higher percentage of body fat and, consequently, will have higher BAC for the same number of drinks. This is a generalization, and does not hold true for a woman who may be very fit, or a man who is somewhat obese. Similarly, for people of the same weight, a person with higher muscle mass will be less effected than a person with more body fat.
The issue of body fat is generally secondary to issues of total body weight. One’s BAC is generally based on total concentration - the total amount of alcohol divided by the total body water. A larger person will generally have more body water, which will cause a lower concentration, and a lower BAC.
Removing Alcohol From The Body
The liver is the primary organ for removing alcohol from the blood, removing over 95% with the rest leaving through breath, urine, sweat, feces, and saliva. Healthy people metabolize alcohol at a fairly consistent rate - generally about one drink per hour. Several other factors can influence this rate, and this rate tends to increase as the BAC is either very high or very low.
Two types of tolerance also come into play with alcohol - metabolic tolerance and functional tolerance. In metabolic tolerance, the liver reacts to greater consumption by producing more alcohol dehydrogenase - the enzyme that metabolizes alcohol - which can result in significantly faster metabolization. Metabolic tolerance is responsible for up to 72% more alcohol being eliminated from the system of a habitual drinker than an average drinker, but also contributes to the destruction of the liver. Functional tolerance allows a body to seem less intoxicated than a person with lower tolerance, causing a heavy drinker with a high BAC to seem less intoxicated than an average drinker with a much lower BAC. However, laws in most states consider the BAC as the primary evidence in DUI and DWI charges, causing a seemingly functional person to be guilty of a DUI for violating the legal limit even when the body seems to handle the alcohol.
Finally, while unexplained to date, studies have shown that women eliminate alcohol from their bodies at a rate nearly 10% higher than average men. However, this faster elimination rate is secondary to the higher general BAC women are likely to experience due to factors above.
Other Factors: Drugs, Fatigue, Health
Because alcohol is a depressant, any depressant drug will increase the effects of alcohol by as much as 10 times, and other drugs may cause unpredictable interactions (such as damage to the stomach lining and decreased blood clotting when alcohol is mixed with aspirin and liver damage when alcohol is mixed with acetaminophen).
Fatigue causes many of the same effects as intoxication, causing symptoms to be amplified or confused. Additionally, your liver is less efficient when overly tired, so drinking the same amount of alcohol will result in a higher BAC than when you’re rested.
When ill, most people suffer from some level of dehydration. Dehydration has a number of side-effects that cause a higher BAC - primarily, less water in the body causes the same amount of alcohol to create a higher concentration, causing a greater intoxication, and higher measurable BAC. Also, dehydration can decrease the efficiency of your liver, causing a higher and longer BAC peak than if you were not ill.
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