A simplified explanation of why the law says you are drunk if you have a BAC (blood alcohol concentration) of .08 or higher, and why the law is wrong..

Since 2004, every state has stated through legislation that if your blood alcohol content is over .08, than you are legally intoxicated and cannot operate a motor vehicle.  But how did they reach this magic number to say that every person is drunk when it is reached?  One would imagine that it is a series of scientific studies that were peer-reviewed, widely accepted as scientific proof.  However, one would be incorrect in making these assumptions because the science behind the .08 number does not hold up.

To better understand why the .08 number is scientifically dubious, one must first consider the basics of the physiology of alcoholconsumption.  Alcohol is a very light liquid.  As it is consumed it is diffuses quickly into parts of the body that have some type of water content; the more water in that particular part of the body, the more rapidly alcohol is absorbed into it. For instance, blood is mostly water, so alcohol dissipates very quickly into it.  Organs, (read: the brain) have much less water and therefore absorb alcohol at a much slower rate.  As the alcohol is absorbed through the lining of the stomach and small intestines, it gets in the bloodstream via the portal vein.  From here, the alcohol moves to the liver, then to the right side of the heart, and then the lungs.  From the lungs, it then moves into the left side of the heart where it is finally pumped into the general circulatory system.  Once in the general circulatory system, it can then finally move into the brain, the part of the body that actually becomes intoxicated.

One can already see where the basic problem lies.  No law enforcement agency in the country tests the fluids in the brain (nor should they!) yet that is where the intoxicating level of alcohol must be absorbed to reach any type of inebriated state.  The tests performed instead measure the level of alcohol in the blood, urine, or breath, all places where the alcohol travels in a much higher concentration before it gets to the brain.  So why then, do we continue to permit shoddy science to fill our jails?

There are several answers to this question.  First, it is hardly a popular political position to come out in any way in favor of driving while intoxicated.  Legislators appearing "soft on crime" face a tough reelection battle.  Secondly, groups  such as MADD have huge lobbying budgets which go to fund these very candidates and ballot initiatives.  But where is the science behind their claims that .08 is the magic number?

The answer comes from the 1930's, when a Sweedish scientist named Erik Matteo Prochet Widmark published a study identifying the average absorption and elimination rates of alcohol.  He found that there was an average number which can be put into mathematical calculations that can show what someone's likely overall body alcohol content is (including the brain) by measuring the amount of alcohol in the blood.  This number (the Widmark Factor R) is the ratio between the alcohol in the whole body divided by the alcohol in the blood. It must be noted here however, that this is only an average, as Widmark's own study showed a range of .46 to .86 in men, with an average number of .67.  This number was different for women because of physiological differences between the sexes.  Furthermore, the study only consisted of 20 men and 10 women, which is hardly the representative sample necessary to derive legislation supposedly based on science in all 50 states. Finally, the test was only conducted on these 30 people with empty stomachs and by consuming the alcohol all at once, which does not account for the variety of real-world differences in the consumption of alcohol.

The methodology to come up with the brain/blood/urine/breath number of .08 based on averages is obviously flawed.  But more importantly, its conclusions are pointless if applied to individuals.  Why have an average number, when individuals vary so greatly?  An individual's alcohol tolerance can vary greatly to the next persons.  Some people might have had a large meal before drinking, others on an empty stomach.  There are numerous differences between men and women as well.  .  Compared to men, women do not have as much of the enzyme in the stomach lining (gastric alcohol dehydrogenase) that breaks down alcohol which results in different BAC readings.  Even the menstrual cycle and medications that affect the menstrual cycle have an effect on alcohol absorption.

The bottom line is, when deciding whether or not to send someone to jail or take away their driver's license, the "average" is not good enough.  We should demand more scientifically rigorous methods of determining when someone is intoxicated or not.