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Cases of caffeine overdose are relatively common and result from the lack of understanding of the effects of caffeine on the body and of how much caffeine one can handle.
Everyone is affected by caffeine differently. It depends on various factors including: (1)
- Caffeine allergy;
- Sensitivity level – genetic factor;
- Body weight;
- General health;
- Level of tolerance;
- Dose of caffeine in one sitting. To see a list of caffeinated products, click here;
- The daily amount consumed;
- Any contraindication taken at the same time (e.g. other drugs).
Effects of caffeine intake depend on your sensitivity level
For the majority of the population, studies have shown that a safe daily caffeine intake is about 400mg (about 4 cups of coffee).
This amount not only doesn’t cause negative effects, but rather a range of positive health benefits.
A small percentage of the population, however, presents signs of caffeine sensitivity to these amounts. For those people the safe caffeine daily intake is lower and varies between individuals. For some, even only one cup of coffee may contain too much caffeine.
Our sensitivity to caffeine is determined by our genetic makeup.
The sensitivity level depends on a combination of various genes, making a categorization very complex.
For most of the population, it can be simplified into three caffeine sensitivity groups.
- Group 1: Caffeine sensitive people
For this group, a very small amount of caffeine (e.g. a few sips of coffee) can trigger caffeine overdose symptoms (see below).
Usually one coffee, coke, Red Bull, or even black tea is enough to set off a range of unpleasant side-effects of caffeine overdose.
Other products such as chocolate, tea or decaf coffee may be acceptable, depending on the extent of the sensitivity (subject to self-testing).
This group of highly caffeine-sensitive people are usually not included in caffeine studies, since they most likely don’t drink caffeinated drinks, and if they did, the overwhelming caffeine side effects would completely distort the results, preventing them from taking part in these studies.
Reasons for caffeine sensitivity
The reason for such a strong reaction to the caffeine intake is the individual’s genetic makeup. These individuals belong to the so-called slow caffeine metabolizers group.
Various genes are responsible for how much of the caffeine-metabolizing enzymes are being produced in the body.
In the case of highly caffeine sensitive individuals, the combination of these genes produces a low amount of these enzymes, prolonging the time caffeine takes to be broken down and excreted from the body.
What happens is that caffeine continues to circulate in the body exerting its powerful effects for much longer.
The consequences can be quite serious. If you are a slow metabolizer (or caffeine sensitive), the risk of a heart attack increases if you drink 2-3 cups of coffee per day. The risk increases the more coffee that you drink.
If one cup of coffee causes caffeine overdose symptoms, it most likely means that you belong to this group and, therefore, should reduce or eliminate caffeinated drinks and foods from your diet.
If you like the taste of coffee, try decaffeinated coffee. The amounts of caffeine in decaf coffee are very small (see the table below).
REMEMBER: the health benefits of caffeine (especially amounts such as 400mg) apply to those that don’t have a problem breaking it down.
- Group 2: People with normal sensitivity to caffeine (moderate to high caffeine users)
This group includes the majority of the population that can have about 400mg of caffeine per day, without experiencing any negative health consequences.
It has been shown through many studies that this amount of caffeine daily, which is equivalent to about 4 cups of coffee, is associated with many health benefits such as the greatest reduction in the all-cause mortality risk, and 300mg per day (about 3 cups of coffee) the highest decrease in the mortality risk due to cardiovascular diseases. (2)
Some people in this group may experience a number of mild caffeine overdose symptoms after drinking more than 2-3 standard coffees per day or double/triple coffee shots.
A common symptom is difficulty sleeping, especially when caffeinated drinks are consumed in the afternoon.
People in this subgroup are usually the morning coffee drinkers.
You can establish your limit by trial and error through monitoring the amount of caffeine you consume per day, the single doses and the time of the day that you are drinking it.
If you experience any symptoms of caffeine overdose you can:
- reduce caffeine intake the next day by one unit (e.g. 50-100mg or one coffee less);
- avoid taking caffeine before going to sleep or in the afternoon;
- change the caffeinated drink or food to another with lower caffeine contents (e.g. swap coffee for decaf coffee, tea or a piece of dark chocolate).
Adjusting the amounts of caffeinated products and observing your body’s reaction should take you a few days to one week.
- Group 3: People with low sensitivity to caffeine
This group includes “heavy” (4-6 cups of coffee per day) to “very heavy” (more than 6 cups of coffee per day) coffee drinkers.
These individuals can handle more than 600mg of caffeine per day and drink coffee just before going to sleep, with no effects on the sleep quality and no caffeine overdose symptoms.
This group mainly experiences desirable effects from having caffeine. (3)
This group is called fast caffeine metabolizers. In these individuals, the combination of genes responsible for the production of caffeine metabolizing enzymes works at its best.
Fast metabolizers are able to quickly break down and remove from their bodies, caffeine and other drugs.
However, the negative side is that this group often increases the caffeine intake to extremely high levels, between 10 and 18 cups of coffee per day, simply because they don’t experience overdose symptoms (at least for a while).
Prolonged overconsumption of caffeine has its consequences: it leads to caffeinism – a combination of dependency and high and frequent caffeine intake.
Caffeinism is accompanied by caffeine overconsumption symptoms and, in the long term, leads to more serious conditions such as peptic ulcers or Gastroesophageal Reflux Disease (GERD).
If you belong to this group and although you feel that you can build your caffeine tolerance to over 6 coffees per day without experiencing any negative symptoms, try to stay in the range of 3-5 coffees or equivalent caffeinated drinks.
How much is too much caffeine?
The following images show how much caffeine is consumed per age group and which caffeinated drinks are most popular in the U.S. (4)
Are these amounts safe?
If you have caffeine allergy, no amount of caffeine is safe. Caffeine allergy, also called caffeine hypersensitivity, is very rare and the affected individuals should avoid caffeine altogether due to a potentially life-threating reaction. (5, 6, 7, 8)
Otherwise, although there are some general recommendations available, there are currently no official guidelines for the safe daily intake of caffeine, such as the “upper limits” for vitamins or minerals.
Information on the negative health effects have been published from the analysis of the effects of caffeine intake.
- Children – 3mg of caffeine per kg of body weight per day;
- Children ages 5-12 – total of 95mg per day (approximately 2 cans of cola);
- Adults – 210mg per day (approximately 3 cups of instant coffee).
Studies conducted on people that are not sensitive to caffeine, (moderate to high caffeine users), show that about 400mg of caffeine per day is considered the safe limit.
More sensitive consumers however, can handle only up to 210mg of caffeine per day (1-3 cups of coffee).
NOTE: these limits don’t apply to everybody, since they also depend on the level of the individual’s sensitivity to caffeine.
In summary, how much caffeine is safe depends on the individual’s ability to handle caffeine.
When unpleasant caffeine overdose symptoms are detectable, it means that the limit has been crossed.
Based on the scientific data from various studies, these are the average safe limits above which negative effects are observed:
- Pregnant women, individuals with caffeine allergy and those who are highly sensitive to caffeine should avoid caffeine intake altogether;
- Although it may be not a good idea for children to have any caffeine at all, children should not consume amounts of 3mg or more per kg of body weight per day, due to the onset of anxiety symptoms;
- Children who are 5-12 years of age, should not consume more than 95mg of caffeine per day;
- Adults with a small degree of caffeine sensitivity should limit their consumption to about 210mg of caffeine per day (1-3 coffees).
Since the sensitivity levels vary between individuals, establishing your own limit is subject to experimentation;
- For adults that are least sensitive to caffeine (moderate, heavy and very heavy caffeine users) about 400mg of caffeine (about 4 cups of coffee-equivalent) is not only a safe amount but also the most optimal daily amount for the widest range of health benefits caffeine can offer.
This optimal amount of caffeine also applies to very heavy users, who are those that can handle 600mg or more (6 coffees or more) without experiencing any symptoms.
While 400mg per day is related to the optimal health and is safe, larger amounts (600mg or more) may lead to caffeinism and generally are associated with decline of health benefits.
Common caffeine overdose symptoms
The most common caffeine overdose symptoms vary in intensity and duration between individuals.
They may occur in any of the above groups depending on the dosage.
Even very heavy caffeine consumers can experience these symptoms if having 4 coffees in one sitting.
Caffeine overdose cases are quite common in the United States. (13)
The common caffeine symptoms are:
- Bad mood
- Changes in alertness
- Difficulty sleeping
- Discomfort in abdomen
- Increased thirst
- Increased urination – applies to supplements rather than coffee or tea which don’t have a diuretic effect. (read more..)
- Headaches or migraines
- Increased heart rate
- Increased blood pressure
- Lack of concentration
- Muscle twitching
Severe caffeine overdose symptoms
- Trouble breathing
- Insomnia (17)
- Cardiac arrest (especially in young people) (18)
- Possible death (read below).
Rhabdomyolysis describes the destruction of muscle tissue, where muscle fibers break down and release their contents to blood which may result in kidney failure. (19)
Rhabdomyolysis associated with excessive intake of caffeine is rare, but worth considering. (20)
Fatal dose of caffeine
A fatal acute dose of caffeine is estimated by the US Food and Drug Administration (FDA) at above 170mg per kg of body weight.
For example, if an average coffee contains 100mg of caffeine, a 70kg person would need to consume over 119 coffees to reach that limit.
Although rare, caffeine related deaths do occur.
How to prevent overdose of caffeine
- Establish which sensitivity group you think that you belong to;
- Experiment to find what amounts of caffeine don’t trigger common, mild overdose symptoms. Test for various caffeine doses, daily caffeine amount and the time of the day you are having caffeinated products.
- Stick to that symptom-free dose or daily amount, or less;
- Get familiar with the caffeine overdose symptoms and once any of these symptoms occur, stop caffeine intake immediately. Reduce caffeine intake the next day;
- If more severe symptoms occur, seek medical help.
Caffeine overdose treatment
Common caffeine overdose symptoms are not necessarily a medical emergency. If you feel a little anxious or irritated after one too many coffees or energy drinks, just wait for these symptoms to wear-off.
When you experience more severe symptoms, it might be a sign of caffeine poisoning. You should seek medical help immediately.
Caffeine poisoning should be treated seriously and the treatment approach by the medical professional is similar to other types of poisoning.
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