Understanding Blood Alcohol Content (BAC levels)

Contributing co-author: Andrew Chen

Blood Alcohol Content (BAC) is a measure of alcohol concentration in a person’s bloodstream. The more a person drinks, the higher their BAC and the more they experience alcohol-related impairments. The following table shows the behavioral, physical, and mental changes brought on by alcohol at various BAC levels:

Progressive Effects of Alcohol with rising BAC levels

Blood Alcohol
Concentration
Changes in Feelings
and Personality
Physical and Mental
Impairments
0.01 — 0.06 Relaxation
Sense of Well-being
Loss of Inhibition
Lowered Alertness
Joyous
Thought
Judgment
Coordination
Concentration
0.06 — 0.10 Blunted Feelings
Disinhibition
Extroversion
Impaired Sexual Pleasure
Reflexes Impaired
Reasoning
Depth Perception
Distance Acuity
Peripheral Vision
Glare Recovery
0.11 — 0.20 Over-Expression
Emotional Swings
Angry or Sad
Boisterous
Reaction Time
Gross Motor Control
Staggering
Slurred Speech
0.21 — 0.29 Stupor
Lose Understanding
Impaired Sensations
Severe Motor Impairment
Loss of Consciousness
Memory Blackout
0.30 — 0.39 Severe Depression
Unconsciousness
Death Possible
Bladder Function
Breathing
Heart Rate
=> 0.40 Unconsciousness
Death
Breathing
Heart Rate

BAC levels can be accurately measured through blood, breath, or urine tests. Currently, the legal limit to drive in the U.S. is .08 for individuals over the age of 21. That limit is similar to those used in other states, but there is some variation.

How many drinks for a BAC of .08?

The answer to this question is a little more complicated than it seems. Alcohol affects everyone differently. In general, smaller individuals reach higher BAC levels more quickly than larger individuals, fatter individuals reach higher levels more quickly than muscular individuals, and women reach higher levels more quickly than men. These factors are all related to the amount of water present in the body. The more water a person has in their body, the more diluted the alcohol will be in their blood. (smaller individuals have less water than bigger people, fatty tissue has less water than muscle, and women typically have a higher % of body fat than men).

Chronic drinkers can develop a tolerance to alcohol, allowing them to metabolize alcohol more quickly and giving them added resistance to the functional impairments of alcohol.

Furthermore, alcohol can affect the same person differently under different circumstances. Eating before drinking can delay alcohol absorption and reduce a person’s peak BAC levels by as much as 40%. Exhaustion, illness, and dehydration impair a person’s ability to metabolize alcohol, promoting higher BAC. Depressed mood and stress can also magnify the effects of alcohol. Finally, medications can react with alcohol, potentially causing serious health complications.

You’ve had too many – can you lower BAC?

Contrary to popular belief, there is no magic food or drink that can lower your BAC levels. Exercising and taking a cold shower will also do nothing to lower BAC. BAC levels will only decrease with time. On average, a person metabolizes alcohol at a rate of one drink (0.5 oz alcohol) per hour. Spacing out drinks is a good way to manage BAC levels as it gives your body time to metabolize alcohol while delaying further increases in BAC.

Understanding your body is the first step towards preventing dangerous BAC levels. Plan ahead make sure you don’t ruin your night or someone else’s by drinking more than you can handle.

Additional Resources:

BAC table for men

BAC table for women

Check out the Virtual Bar at www.b4udrink.org for a really fun way to learn about your own limits!

2 Replies to “Understanding Blood Alcohol Content (BAC levels)”

  1. I feel that this is very useful and if more people knew about this, they would be more cautious of how much they drank especially if they are going to be driving. I think its interesting that no food or drink can lower your BAC level, I thought that the more you ate it absorbed the alcohol and helped, little did I know. Another helpful website that I found was http://www.ou.edu/oupd/bac.htm. This site has multiple charts that show BAC and levels of impairment due to number of drinks during a certain time as well as to body weight. It also lists some myths and true facts of drinking that can be helpful as well.
    There is a lot of great facts on this blog! I learned a lot of new information!

    Thanks

  2. Can an alcoholic who may not wake up and have a drink, but was drinking the previous evening (approximately eight hours prior) wake up and blow a .22 on a breathalyzer. I guess my main question really is whether an alcoholic maintains a blood alcohol level at all times due to their chronic drinking?

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