Blood Alcohol Content - What is it? What Factors Affect it?

By Evan Levow
 on 0101/2929/15151515
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Blood cells abstract

Those who drink know the basics of what blood alcohol content (BAC) is. The police are familiar with the implications of effects of the measurements, but may not know the science behind it. Perhaps the most informed on the subject of BAC is the bartender, who makes a living serving alcohol to tipsy or just plain intoxicated customers on the weekend.

The Science & Biology Of Blood Alcohol Content (BAC)

Blood Alcohol Content is the measure of the amount of alcohol in a person's body. With a BAC of more than 0.08 (equivalent to 80mg/dL or 17mmol/L) a person is considered legally intoxicated in most states. Alcohol affects each person differently depending on personal tolerance, how much food is consumed while drinking, and body weight, as well as other factors like health issues, medications taken and sometimes whether the drinker is a male or female. With a BAC as low as 0.05 a person can begin to experience a sedative effect from the alcohol. His/Her reaction time slows and he/she doesn't think clearly. When the BAC reaches .08%, a drinker loses even more reaction time, reflexes, peripheral vision, depth perception and reasoning skills, which are all necessary functions to drive a car safely.

Certain drinks, foods and medications interact with the alcohol that is being consumed and can intensify or diminish the effects. For example, carbonated drinks like Coca-Cola or Sprite can speed up the absorption of alcohol in the blood stream, which would serve to make a person feel the effects of the alcohol more quickly. Certain medicines taken for asthma, including albuterol, salmeterol and budesonide, can create a false positive BAC even though no alcohol was consumed. The Healthy Drinker about carbonated drinks and alcohol absorption.

Many factors affect a person's BAC. Two people ordering the exact same drink might see very different effects. What can cause one to become chatty and easy-going might do nothing for the other. Here are some of the major things that affect BAC:

Various Factors Affecting BAC

Tolerance for alcohol:

How often a person drinks, how much they typically drink, and how long they have been drinking can affect BAC as the time taken to metabolize the alcohol may be faster or slower.


As mentioned, soda can increase a BAC. Any carbonated drinks can also increase the blood alcohol content, including champagne or soda water. The carbonation causes alcohol to pass through the stomach faster.


Drinking on an empty stomach usually leads to a higher BAC level than someone who has eaten. Having food in the stomach slows absorption into the bloodstream by keeping it in the digestive system longer.


For those who drink after a long day of work, it takes longer to get to a "happy" place. This isn't just because a stressful day seems to make it harder to be happy, but because stress steals blood from the stomach and small intestines and sends it to the muscles; therefore, alcohol doesn't absorb into the bloodstream very quickly.


It takes more to make a young person drunk than it does an older person. The intoxicating effects of alcohol hit more strongly for older people.


Men are blessed with a higher alcohol tolerance in general because they have a higher water content in their bodies than women. In addition, women are lacking in the enzyme dehydrogenase, which breaks alcohol down in the stomach, which also increases the BAC. Read more about gender affecting alcohol consumption here.


Everybody has a different rate of metabolism, which is the rate at which alcohol (or anything really), is processed in the system. In addition, the fluctuation of estrogen in women can lead to intoxication at a lower BAC than normal.

Rate of Consumption:

This is common sense, but the more a person drinks over a period of time, the higher their blood alcohol content will reach.

Fat/muscle content:

Those who are overweight are more likely to reach a higher BAC than those who work out regularly. This is because fatty tissue has a difficult time absorbing alcohol than muscles do, which means more alcohol is left in the bloodstream until it can be metabolized by the liver.

Final Factors & DUI Penalties

Body Type:

This isn't as much about weight as it is about general body type. A person who is tall and skinny may reach a higher BAC than his bodybuilding friend who drank the same mixer, simply because those who weigh more typically have more water in their body, which dilutes the alcohol.

Alcohol content of the drinks:

Some drinks are made stronger than others. Someone who drinks two wine coolers isn't going to have the same BAC as someone who consumes two Long Islands, since wine coolers typically only contain 5-6% alcohol by volume where a Long Island Ice Tea has an alcohol concentration of about 22%


Just as some medications can create a fall positive on the breathalyzer, some medications can increase a person's BAC by affecting how the alcohol is absorbed by the body. Cold and allergy pills are known to intensify the effects of alcohol.

As you can see, alcohol affects everyone differently, but no one is immune to the consequences of being arrested if caught driving under the influence. Understanding BAC is very important when strategizing a defense to a DWI charge.

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Evan Levow - instructor of field sobrietyState V. Chun Button
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Evan Levow
Date Published: January 29, 2015
Evan Levow is the managing partner of Levow DWI Law, P.C., which is a Tier 1 DUI/DWI Best Law Firm. Evan Levow has argued before the New Jersey Supreme Court on landmark DWI breath testing cases such as State vs. Chun. He is also the President Emeritus of the 600 member DUI Defense Lawyers Association.
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