UT University Health Services

Blood Alcohol Concentration

Understanding Blood Alcohol Concentration (BAC) and Setting your Limits

BAC refers to the percent of alcohol in a person's bloodstream. A BAC of 0.10% means that an individual's blood supply contains one part alcohol for every 1000 parts blood. In Texas, a person is legally intoxicated if they have a BAC of 0.08% or higher. Understanding the factors that impact your BAC is an effective way to make informed decisions about your drinking limits and can help you reduce your risk for potential harm while drinking. To learn more about actions you can take to have fun and play it safe, visit this page.

Tolerance and BAC

Tolerance occurs when the body acclimates to the effects of alcohol, due to habitual use. Tolerance does not impact BAC, but rather makes an individual’s BAC feel lower than it actually is. This means that an individual will feel less affected by alcohol, and it will take more alcohol to reach the same physiological response. The development of tolerance doesn’t mean someone can process alcohol more efficiently and BAC levels will still remain the same. This response is an early sign of developing an alcohol dependency.

Factors that impact BAC

Number of standard drinks and rate of consumption

  • BAC will rise relative to the number of drinks consumed and how quickly they are consumed.

Body size and composition

  • Body size determines the amount of space that alcohol has to diffuse throughout the body. In general, a person with a larger build who drinks the same as a person with a smaller build will have a lower BAC due to the amount of space alcohol has to distribute through.
  • Alcohol diffuses more into muscle than fat because muscle tissue has a large amount of blood that flows through it. This means that an individual’s muscle to body fat ratio will impact their BAC, as it correlates to the amount of blood available for alcohol to enter. For example, someone with a higher percentage of body fat will experience a more rapid increase in BAC, as alcohol will become more concentrated in the blood of their muscle tissue.

Testosterone and estrogen levels

  • People with higher levels of testosterone generally have more muscle mass and less body fat than people with higher levels of estrogen. Muscle contains more blood than body fat. The larger volume of blood in those with greater muscle mass allows alcohol to dilute more through the bloodstream and BAC to remain lower.
  • People with higher levels of testosterone are composed of approximately 55-65% water, whereas people with higher levels of estrogen are composed of about 45-55% water. Alcohol becomes more diluted in bodies with greater volumes of water, resulting in lower BAC levels for people with higher levels of testosterone as compared to those with higher levels of estrogen.
  • Individuals with higher levels of testosterone have higher levels of alcohol dehydrogenase, an enzyme that helps break down alcohol. This means that individuals with higher levels of testosterone can more efficiently break down alcohol as compared to individuals with higher levels of estrogen, who have more alcohol enter their bloodstream, resulting in higher BAC levels.
  • Research has found that due to changes in hormone levels, individuals who have periods experience slower alcohol metabolism and higher levels of intoxication in the week leading up to their period. Oral contraceptives and other medications with estrogen also slow the rate at which individuals process alcohol.

Additional drugs or medications

  • Other drugs and medications, even those prescribed to you, can have adverse effects and unpredictable interactions with alcohol. It is important to ask your doctor if any medications you might be taking have harmful effects when taken with alcohol.

Amount of food consumed

  • Food present in the stomach causes the alcohol to move down into the small intestine slower than it would on an empty stomach. While it’s a common myth that food absorbs alcohol like a sponge, it actually causes a “traffic jam” in the body, making the processing of alcohol take longer. This reduces the risk of a rapidly rising BAC level.

Emotional state, mood and level of fatigue

  • Alcohol has a more pronounced effect on those who may be fatigued or under stress. Since alcohol is a depressant, someone who is depressed may experience heightened signs of depression upon drinking.

Menstrual cycle

  • Research has found that due to changes in hormone levels, individuals who have periods experience slower alcohol metabolism and higher levels of intoxication in the week leading up to their period.

Type of beverage or mixer

  • Fruit juices slow down the processing of alcohol because the sugar requires digestion, resulting in a slower rise in BAC. On the other hand, carbonated mixers or drinks can cause BAC to rise more rapidly because the carbonation speeds up absorption.

It is important to note that common strategies used to “sober up,” such as taking a cold shower, sleeping, drinking water and consuming caffeine, do not work to lower BAC. The only thing that can help alcohol leave your bloodstream is time.

Online Calculators

BAC Calculator: Use this calculator to get an approximate BAC level.

Drink Size Calculator: Learn how many standard drinks are in various beverages and sizes of containers.

The Virtual Bar: See how alcohol consumption affects BAC over time.

Sources

Cornell Health. (2019, October 18). Why Biology Matters When It Comes to Drinking Alcohol. Retrieved from https://health.cornell.edu/sites/health/files/pdf-library/Why-Biology-Matters-Drinking.pdf

Office of Substance Use Programs Education & Resources. (n.d.). Tolerance. Retrieved from https://super.stanford.edu/learn/alcohol-drug-info/alcohol-info

Rev. James E. McDonald, C.S.C., Center for Student Well-Being. (2021). Absorption Rate Factors. Retrieved from https://mcwell.nd.edu/your-well-being/physical-well-being/alcohol/absorption-rate-factors/

UCSB Prevention and Wellness Services. (2003, November 13). Alcohol 101: Gender Differences. Retrieved from https://adp.sa.ucsb.edu/sites/default/files/2021-05/alcohol_-_genderdifferences.pdf

Helpful Links

Alcohol and Drugs
Bruce the Bat
Alcohol Overdose and the Bacchus Maneuver
Prescription Drug Misuse
Prescription Stimulant Misuse
Having Fun and Playing Safe
Naloxone / Narcan

Programs and Classes

Individual Consultations
AlcoholEdu and SAPU
Brief Alcohol Screening Intervention for College Students (BASICS)
Center for Students in Recovery
Student Amnesty for Alcohol Emergencies
SHIFT




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