“It takes an average of five hours for the caffeine level to drop by half. After ten to fifteen hours there is not enough left to have any effect,” says Professor Olav Spigset. (Photo: Peter Bernik / Shutterstock / NTB scanpix)

How long are you affected by caffeine?

Some claim they have trouble sleeping if they have had any coffee later than noon. Can caffeine really have that long an effect on the body, or is it all in the mind?

Norwegians are said to be second only to Finns in world coffee consumption per capita. Many Norwegians wouldn’t think of letting a day pass without getting their jolt of java. Some seem to be able to drink cup after cup, even right before going to bed, with no problems. Others say they spin like a top on the mattress if any less than half a day as passed since their last latte.

There are big differences in how alert we become from caffeine, as our tolerances for the drug are individual. But does caffeine decompose in the body at different rates, making this stimulant last longer in some than others?

We asked Olav Spigset, a researcher and professor at the Norwegian University of Science and Technology’s (NTNU)’s Department of Laboratory Medicine, Children’s and Women’s Health. He explained that caffeine can disturb a night of sleep in intricate ways.

Five-hour half-life

A common term in chemistry and pharmacology is half-life. In the coffee context it is the time it takes for a concentration of a substance to be converted an digested or released from the body by 50 percent.

Olav Spigset says that the half-life of caffeine varies.

“The time it takes for the caffeine level to drop by half is an average of five hours. After ten to 15 hours there is no longer enough left to have an impact.”

Spigset explains that the effect of caffeine as a stimulant is still there after it is halved. And among some the half-life is of course shorter or longer than average.

“A half-life of five hours is the average for the population. But for some it can be as little as a half hour. Amongst those whose bodies are slower in this respect it can take up to ten hours. For them, a cup of coffee at noon could cause problems falling asleep at 10 or 11 in the evening. They have so much caffeine left in their bodies they are still being stimulated by it.”

Contraceptive pills and smoking

Enzymes in the liver are what determine how fast the caffeine breaks down. Enzymes are proteins which are found in multiple variations throughout the body and are involved in the chemical reactions going on inside us.

“The caffeine is metabolized in the liver by special enzymes. Concentrations of these enzymes vary between individuals. Certain medications can also have an impact on this decomposition,” says Spigset.

“Some medications speed up the decomposition so more coffee is needed to keep up the stimulating effects, whereas others its break down.”

The professor says that women who are pregnant or use contraceptive pills experience a much slower metabolization of caffeine. This contributes to higher concentrations of it and side-effects such as agitation, the jitters and heart palpitations.

“Another thing is that smokers metabolize caffeine more rapidly than non-smokers. So a smoker needs more coffee to get the same stimulating effect from caffeine. When a person quits the nicotine habit, this decomposition starts going slower again. Many then find they have a lower tolerance of coffee and they have to reduce their intake of it to avoid getting too high a dose.”

Individual differences

Olav Spigset asserts there are also individual caffeine tolerances.

“Caffeine works on receptors in the brain. These are like small locks into which the caffeine fits, like a key, and thus stimulating the brain. If these receptors are stimulated much and often they eventually become less sensitive to caffeine, and then a person gets a higher tolerance. The same amount of coffee gives less of a jolt.”

“If you don’t get the quantity of caffeine you are used to, you can experience abstinence. This can happen for example if you tend to drink loads of coffee at work and then much less at home on weekends. These abstinence symptoms are usually pretty mild, like perhaps a headache. But in principle, this caffeine abstinence is the same mechanism at work as what happens when heavy users of alcohol or drugs suffer abstinence.”


Spigset points out that the quantity of caffeine you consume will of course impact how much is affecting you, even if it doesn’t change the half-life. ScienceNordic’s Norwegian partner forskning.no has previously written that a litre of strong coffee contains about three times as much caffeine as a litre of energy drink and ten times the caffeine as a litre of cola.

“Cola and tea contain less caffeine than normal-strength coffee per decilitre. Energy drinks have lower concentrations of caffeine than coffee, but we often consume larger amounts of energy drink than coffee. This can have unfortunate effects, especially on children and adolescents, who usually have a lower tolerance regarding caffeine.”

This means that your officemate could be right in declining a cup of coffee at two in the afternoon, claiming it can lead to sleep problems. Caffeine’s stimulating effect can indeed make it hard for them to fall asleep many hours later.

“Of course there is always a placebo element in subjective perceptions of conditions, like not being able to fall asleep. But there is definitely a real physiological effect of caffeine on sleep,” says Spigset.


Read the Norwegian version of this article at forskning.no

Translated by: Glenn Ostling

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