So here are some of the basics about alcohol that will enable you to really think about what you (or others who may affect you) are doing.
Levels of Alcohol Impairment
Alcohol is a depressant. It depresses our central nervous system (our brain and spinal cord) so that our functioning is impaired. The more we drink, the more impaired our functioning becomes until we ultimately we die.
There are four levels of alcohol impairment based on how much alcohol we have had to drink and so, in turn, how much alcohol we have in our blood stream. If you look at the table below you will see that at each level our functioning becomes significantly worse.
Level 1: Mild Impairment – 0.0 - 0.05% (i.e. 0 - 50mg of alcohol per 100ml of blood)
(Note: 0.05% is the South African, Australian & New Zealand legal limit for safe driving)
- Mild speech, memory, attention, coordination, balance impairments
- Perceived beneficial effects, such as relaxation
- Sleepiness can begin
Level 2: Increased Impairment – 0.06 - 0.15% (i.e. 60mg – 150mg of alcohol per 100ml of blood)
(Note: 0.08% is the UK legal limit & the USA legal limit for drivers over 21 years of age)
- Perceived beneficial effects of alcohol, such as relaxation, give way to increasing intoxication
- Increased risk of aggression in some people
- Speech, memory, attention, coordination, balance further impaired
- Significant impairments in all driving skills
- Increased risk of injury to self and others
- Moderate memory impairments
Level 3: Severe Impairment – 0.16 - 0.30% (i.e. 160mg – 300mg of alcohol per 100ml of blood)
- Speech, memory, coordination, attention, reaction time, balance significantly impaired
- All driving-related skills dangerously impaired
- Judgement and decision making dangerously impaired
- Blackouts (amnesia)
- Vomiting and other signs of alcohol poisoning common
- Loss of consciousness
Level 4: Life Threatening – 0.31 - 0.45% (i.e. 310mg – 450mg of alcohol per 100ml of blood)
- Loss of consciousness
- Danger of life-threatening alcohol poisoning
- Significant risk of death in most drinkers due to suppression of vital life functions
Testing for Alcohol
When you drink alcohol, it goes into your stomach and small intestine. It then gets absorbed into your blood, which carries it through your body and into your brain and lungs. You exhale it when you breathe.
When it comes to testing for alcohol there are different types of tests which measure your breath, saliva, blood or urine.
Each of these tests has the same goal: to check how much alcohol is in your body. Usually, you get a result called the blood alcohol concentration (BAC). It’s a small number, like 0.05.
The blood alcohol test measures how much alcohol is in your blood. It measures levels of alcohol per 100ml of blood.
A breath alcohol test measures how much alcohol is in the air you breathe out. It looks at how much alcohol there is per 1000ml of breath. The device (known as a breathalyser) uses that measurement to estimate how much alcohol is in your blood.
It’s important to keep in mind that the more your drink the more impaired your cognitive functioning becomes – so if you are over the limit you may think that you are quite capable of driving safely, when in fact you just can’t. Unfortunately, if you are over the limit you won’t be thinking rationally anyway, so you won’t be keeping this in mind! Make arrangements to get home safely before you start drinking.
What Does “Over the Limit” Mean?
Sure it means driving when you have had too much alcohol to drink, but in real terms what is too much?
The limits for driving safely are different for different countries around the world.
In South Africa, the legal blood alcohol limit is less than 0.05 mg per 100 ml and the legal breath alcohol limit is less than 0.24 micrograms in 1000 ml of breath.
In the UK, the legal blood alcohol limit is less than 0.08 g per 100 ml and legal breath alcohol limit is less than 0.35 micrograms of alcohol per 1000 millilitres of breath.
The limits are usually written as a percentage, e.g.
- SA = 0.05% (50mg of alcohol per 100ml of blood)
- UK = 0.08% (80mg of alcohol per 100 ml of blood.
Anything over the limit is considered to be too much alcohol and it is illegal to drive.
How Much Alcohol can I Drink and Still be Under the Limit?
The rule of thumb is a maximum of one unit of alcohol per hour, which constitutes 10ml of pure alcohol, based on an adult weighing 68kg. (If you weigh less than 68kg your body will need more time to process the same amount of alcohol).
One unit is equal to 0.02g blood alcohol. Our bodies can process only one unit of alcohol each hour, which means that 2 drinks within the space of one hour will put you over the limit.
It doesn’t matter what you’re drinking, the important thing to know is how strong your drink is, and how much you’re having. For example, a single (25ml) shot/shooter is only ½ unit in most instances, but one pint of 5% lager contains nearly 3 units.
Always check the label - checking your drink’s ABV (alcohol by volume) will give you a guide to how strong it us. The ABV tells you what percentage of the drink is made up of alcohol. Spirits like gin and whiskey have a higher Alcohol by Volume (ABV) than most other alcoholic drinks and are often around 40%. In comparison, lager sits around 5% ABV and wine at 12% ABV. The higher the percentage, the more alcohol there is.
Once the alcohol is in your system your liver is going to need time to process it, and restricting yourself to only one unit per hour will give your body the time it needs to stay sober in the eyes of the law. There are no quick-fix solutions. Nothing can lower BAC except time. Drinkingcoffee to get sober is a myth, as is taking a cold shower or drinking a litre of water.
But how much is a unit of alcohol? This is where many people go horribly wrong, assuming for example that one unit of wine is a full glass of wine or a full bottle of beer. But actually one unit of wine (with an alcohol content of 12% to 14%) is only two mouthfuls! And one unit of beer or spirit cooler (with 5% alcohol content) is equal to only two thirds of a bottle.
Let’s take a look at different drinks and how much of it makes up a unit.
Units of Alcohol per Drink Type
1 unit is equal to 0.02g blood alcohol. (Source: Drunk Driving Laws in South Africa)
|Drink||Alcohol by Volume (ABV)||Units|
|Small glass (125ml) of wine||13%||1.6|
|Medium glass (175ml) of wine||13%||2.3|
|Large glass (250ml) of wine||13%||3.2|
|Large glass (250ml) of wine||14%||3.3|
|Bottle (750ml) of wine||13%||9.7|
|Single shot/shooter (25ml)||40%||½ unit in most instances|
|Spirit cooler (300ml)||5%||1.25|
|Bottle beer (330ml)||5%||1.5 (possibly more)|
|Bottle cider (330ml)||5%||2|
|Pint Cider (About 500ml)||5%||2.8|
|1 x cocktail||varies||Between 2 and 4 units|
Remember it takes your body approximately 1 hour to process 1 unit of alcohol (if you weigh more than 68kgs), so you can use the information above as a guide to work out how long it takes for the alcohol to leave your system. (For people under 68kgs, add extra time).
Factors That Affect Blood Alcohol Content (BAC)
Your blood alcohol content (BAC) may go up as soon as 15 minutes after drinking and it is usually highest about an hour after you drink, but how fast your BAC rises and how long it stays that way will depend on several things:
Your weight. The heavier you are, the more water is in your body. The more water, the more the alcohol gets diluted.
Your sex. Alcohol doesn’t affect men and women the same. Men have higher levels of a stomach enzyme that helps break down alcohol, so they process it faster. Women typically have less water and more fat. Hormonal changes in women also can affect the BAC.
How many drinks you had, how strong they were, and how fast you drank them. The more alcohol you drink each hour, the faster your BAC rises.
How much you ate. A full belly, especially high-protein foods, will slow the processing of alcohol.
Drinking and Driving: What are Your Chances of Having an Accident?
You have already seen in the table above that alcohol causes significant impairments in all driving skills. Slower reaction time and distorted vision are two examples of the impairment alcohol causes. There are many more.
The reality is that after only one unit of alcohol, your chances of being in an accident are doubled, and even if you are still in the legal limit of 0.24mg of alcohol per 100ml of blood (level 1), you are four times more likely to be in an accident.
In South Africa 40% of drivers who die on the road have alcohol levels in excess of 0.08 mgs / 100 ml (level 2).
The effects of a heavy night of drinking could well affect your driving ability the next morning. You could still even be over the legal limit. This is the reason why pilots, scuba divers and operators of heavy machinery have to stop consuming alcohol a minimum of 24-hours before undertaking such activities.
How Much Alcohol is it Safe to Drink per day?
If we are talking in terms of units of alcohol, men and women are advised not to drink more than 14 units a week on a regular basis.
Remember, one pint of 5% ABV cider contains 2.8 units. So drinking just 5 pints of 5% ABV cider in a week will take you to the limit of the low-risk guidelines of 14 units. And drinking just six pints of 4% ABV lager, in a week, will take you to the limit of the low-risk guidelines of 14 units. When it comes to wine, it should be under one and a half bottles of wine per week.
Spread your drinking over 3 or more days if you regularly drink as much as 14 units a week.
If we are talking in terms of numbers of drinks, the dietary guidelines for Americans define moderate drinking as up to one drink per day for women and up to two drinks per day for men under the age of 68 years (over 68 years is 1 drink per day).
But most adults don’t drink every day, so it’s important to focus on the amount people drink on the days that they do drink. Even if women consume an average of 1 drink per day, per week, or men consume an average of 2 drinks per day, per week, binge drinking increases the risk of experiencing alcohol-related harm in the short and the long-term. (Binge drinking is defined as consuming 5 or more drinks on one occasion for men or 4 or more drinks on one occasion for women).
Drinking at levels above the moderate drinking guidelines significantly increases the risk of short-term harms, such as injuries, as well as the risk of long-term chronic health problems, such as some types of cancer.
Another issue to bear in mind is that alcohol is a diuretic (makes you urinate) and as such it is a huge dehydrator. You should try to limit your intake of alcohol, but if you are going to drink alcohol aim for at least a one-to-one ratio with water.
Of course some people should not drink alcohol at all, such as those who:
- Are pregnant or trying to fall pregnant.
- Have certain medical conditions or are taking certain medications that can interact with alcohol.
- Are recovering from an alcohol use disorder or if they are unable to control the amount they drink.
Comparison: Alcohol vs Lack of Sleep
Although the focus of this article is alcohol, it is interesting and useful to compare the effects of lack of sleep with the effects of drinking alcohol.
If you go 12 consecutive nights on six hours’ sleep, it’s equivalent to a blood alcohol of 0.1%, (level 2) which is marked by slurred speech, poor balance, and impaired memory. In other words, you’re functioning as if you are drunk.
The performance of someone who has been awake for 24 hours is equivalent to that associated with a blood alcohol level 25% more than the current UK legal limit of 0.8% (level 2). This makes them seven times more likely to have an accident.
The message here is that getting enough sleep is really important if you want to live a happy, healthy lifestyle! As is staying under the limits when it comes to drinking alcohol.
You can read about how to ensure that you get good quality sleep in my article “Insomnia”.
So Cheers! Here’s to your health!