While drinking the same amount of alcohol, each person’s blood alcohol concentration may be different.
Meaning of alcohol concentration
Even very small amounts of alcohol can affect your concentration, judgment, and performance. You may feel fine, but your reflexes will be slower than normal and your ability to concentrate will be reduced.
This makes it difficult to perform activities that require the skill, concentration, or safety of others. That’s when you drive, play sports, or use complex machinery.
Blood alcohol concentration can be measured using a breath alcohol meter or analyzing blood, saliva, and urine samples.
There are many different factors that affect each person’s blood alcohol concentration. Illustration photo: Shutterstock
Factors affecting alcohol concentration
The body usually takes at least 1 hour to digest 1 unit of alcohol. According to the Ministry of Health’s instructions, one unit of alcohol is equivalent to: 3/4 bottle or 3/4 can of 330ml beer (5%); 1 cup of draft beer 330ml (4%); a 100 ml glass of wine (13.5%); a small glass/shot glass of 40ml (30%) brandy.
However, two people can drink the same amount of alcohol but have different blood alcohol concentrations. According to the Australian Alcohol and Drug Association, there are many individual factors that influence how the body breaks down and absorbs alcohol:
Body size
Normally, the alcohol concentration in small people will be higher when drinking the same amount of alcohol.
Hungry stomach
If you drink alcohol on an empty stomach, the alcohol will penetrate your blood quickly, making you drunk sooner. However, eating a meal before drinking does not mean you will not be drunk and can drive safely.
Body fat
Our fat cells hold much less water than our muscles. This means the alcohol is not absorbed and remains in your blood until it is broken down by the liver. People with higher body fat will have higher alcohol levels.
Liver health
The liver does most of the alcohol breakdown. People with liver disease or liver damage will not be able to process alcohol as quickly as people with healthier livers.
Age
As you get older, the speed at which your body processes alcohol decreases because your liver may be smaller. This means alcohol can stay in the blood longer and increase alcohol levels.
Sex
Women typically have a higher body fat percentage, lower body water, and less alcohol-degrading enzymes than men. Therefore, in women, alcohol is processed more slowly and will remain in the blood longer.
Alcohol tolerance
If you haven’t drank much alcohol, your tolerance will be lower. Your body is not used to it and the result is a higher blood alcohol concentration.
Medicine
Many drugs need to be broken down by the liver, just like alcohol. If you drink alcohol while taking these medications (e.g. birth control pills), your liver will process the alcohol more slowly, leading to higher blood alcohol levels. If you are taking any medications, talk to your doctor or pharmacist about whether you can drink alcohol.
Alcohol content of wine
Not all drinks have the same amount of alcohol. The higher the amount of alcohol in wine, the higher your blood alcohol concentration.