BLOOD ALCOHOL CONTENT (aka BAC)

We learned as children that tiny and hopefully nutritious parts of the things we eat and drink are passed directly into our bloodstream.  It happens when we drink an alcoholic beverage, too.  Molecules of alcohol pass through the stomach lining and mix in with our blood.  This mixture of alcohol in the blood can be accurately measured.  BAC stands for Blood Alcohol Content and this is a direct measurement of actual alcohol flowing with your blood through your body.

Around the world, BAC is recognized as the standard tool for setting a legal limit for intoxication while driving.  Although the math behind determining BAC differs in some countries, the numeric result is the same.  Blood may be thicker than water, but its mass is about the same.  A gallon of water and a gallon of blood weigh about the same.  If you have .05 grams of alcohol in 100mL of blood, it is the same as saying .05% of your blood is alcohol. They use milligrams in Europe instead of grams, so a BAC of .05 in America is the same as a BAC of .50 in Great Britain. What matters to YOU is how the law treats all of this when you drive.

Extensive scientific study has determined the typical effects of alcohol depending on varying BAC levels.  In other words, by obtaining your BAC, law enforcement can tell how drunk you are with fair accuracy.  How fair?  It doesn't matter.  It's the law.  Studies of BAC levels have determined a magic number which identifies one as too intoxicated to drive safely.  In all 50 states of America, the magic number is .08.  .08 is the highest BAC recognized as a legal limit in many parts of the world.  Most countries set lower legal limits than America including Canada which lowered their legal limit from .08 to .05 in 2010.

The level of .08 is chosen because by the time you reach a .08 BAC, your coordination is notably affected.  But at a .05, sedation and slowed reaction time are the key effects on your body.  These alone are enough to impact your driving.

It is important to remember that the effects of any amount of drinking are dependent on more than just the alcohol itself.  If you were a guy like me around my shape and size, and we both consumed the same drinks, you may not outwardly show any signs of being drunk.  Meanwhile, I may be looking up at you from the floor as I try to feel my legs.  You have a higher tolerance than I do.  Does this mean that it's OK for you to drive?  No.  Not if your BAC is .08 or over.  Because of my low tolerance to alcohol, let's say I drank only half as much as you and achieved a mere BAC of .04.  I may still be too drunk to drive safely.  My reaction time may be slow, my level of alertness low, or maybe I'll just.. get… really tired… and zzz... Er, yeah.  So remember that although 08 is the magic number, you really need to reconsider driving ANY time you've been drinking.  My tolerance may have been affected if I was on medication, fasting, fatigued, or lying and drinking more than I said I did.  Your tolerance could be much higher than mine if you were a chronic drinker.

.08 is considered the legal threshold for adult drivers.   If you are under 21 years old, you can expect that being caught with ANY alcohol in your blood while driving will result in arrest.  It's called Zero Tolerance and it's Nation-wide.  We suggest you check out our If You are Under 21 lesson.

So what are the factors that determine how much alcohol winds up in your blood?  How do you get to a .08 and what happens to you along the way?  How long does it take for your BAC to go back down?  Reputable sources for this type of information include David J. Hanson’s Alcohol Abuse Prevention website ,  and the NHTSA's ABC's of BAC.  What follows is information gleaned from these sources along with our usual DrinkingAndDriving.Org slant on the topic.

The Basics

Standard BAC charts come in two flavors – male and female.  This is because the amount of body fat one has for a given weight affects how much alcohol makes it to the bloodstream.  Alcohol is not absorbed by fatty tissue.  In "normal healthy" people, women have more body fat than men.  The alcohol has less body to work on and is more concentrated.  In these charts, one drink is equal to 1 1/4 oz. of 80-proof liquor, 12 oz. of beer, or 4 oz. of wine.  Drinks are consumed within one hour.  Hover your mouse over a BAC result to see the physical effects on your body.

FYI,  while not represented in our charts, a .50 typically results in death.  You can see that an 11^th drink may be fatal.  Stronger drinks will put you at higher BAC rates quicker.  1 ½ oz. shots of 100-proof liquor will lower the fatal dose by a couple of drinks.

Again, these tables are very general, but very good guides.  There are a number of other factors which will alter the rate at which alcohol enters your blood and the rate at which it dissipates.  In other words, you can slow down or speed up alcohol's effects, but you can't stop them.  To understand the impact of these variables requires an understanding of how you get drunk in the first place.  So let’s take a tour of your Gastrointestinal System …

The Factory

Three key organs, the stomach, intestines, and liver dictate how quickly your BAC rises and lowers once you begin drinking.

First stop, the stomach.  The stomach absorbs alcohol into the blood through diffusion.  But it does so more slowly than the intestines.  The stomach has a valve at the end called the pyloric valve.  When we eat food, this valve closes so the food can stay in the stomach for digesting.  Therefore, eating food can slow down the rise of your BAC level.

Your intestines are far more efficient at diffusing alcohol into your blood than your stomach.  If you drink on an empty stomach, your pyloric valve is open and more of the alcohol reaches the intestine quicker.  The intestine can then diffuse more of it into your bloodstream quicker, thus raising your BAC more quickly.

The liver's role is to eliminate the alcohol.  It does so by producing an enzyme called alcohol dehydrogenase which metabolizes the alcohol.  In chronic drinkers, the constant higher production of this enzyme tends to metabolize alcohol more quickly, thus lowering their BAC more quickly.  However, the proliferation of these same enzymes eventually begins to damage the liver.  95% of the alcohol you drink leaves your body this way.  The rest is released in your sweat, breath, milk, saliva, and urine.  For the average person, an average drink will take about an hour to leave your body.  In BAC numbers, this would be lowering your BAC by .01 every 45 minutes or so.

Other Considerations

Medications

Alcohol is a depressant. If you take any other depressant drugs, the effects of alcohol can be multiplied up to 10 times.  Understand, your BAC will be the same.  But the EFFECTS will be far stronger.  It is very important to always follow instructions for all medications, not just prescribed medicine.  Even aspirin or acetomyophin can be harmful when mixed with alcohol.  Always use caution.

Health

If you are tired, or fatigued, you will achieve a higher BAC than if you are well-rested.  Your liver will work more slowly when you are tired, and process your alcohol more slowly.  Illness can lead to increased BAC levels because when we are sick, we are frequently dehydrated.  With less water in our body, more of the alcohol can enter the blood quicker.

Conclusions

When you drink alcohol, it enters your bloodstream.  There is no way to stop it.  Once in your blood, physiological effects are felt.  These physiological affects rise and ebb over time corresponding to the amount of alcohol in your blood.  BAC is a measurement of how much alcohol there is in your blood.  Only TIME can reduce your BAC.  The higher your BAC, the longer it takes to return to safe driving levels.

Overwhelming evidence shows what happens to our bodies at different BAC levels.  This makes BAC a direct and simple tool in determining when a person is unfit to drive.  This explains why BAC is used around the world for this purpose.