By Aristos Georgiou
Science and Health Reporter
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Are you the type of person who can have a coffee before bed and still sleep easily? Or does a single espresso in the morning give you the jitters?
Well, according to a new report, coffee drinkers fall into three main groups, depending on their sensitivity to caffeine.
The study—produced by the Institute for Scientific Information on Coffee—examines existing research to explain how the body metabolizes caffeine, and why some people are affected by it more than others.
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Two main genetic factors dictate how an individual responds to caffeine, determining the speed at which the liver metabolizes the compound and how the central nervous system reacts to its stimulating effects.
In light of this, the report outlines three different levels of caffeine sensitivity:
- High sensitivity to caffeine: Slow metabolism in the liver and strong binding in the central nervous system. Even small amounts of caffeine will cause a stimulating effect and higher doses may cause sleep problems, as seen in a minority of people.
- Regular sensitivity to caffeine: The balance between caffeine inactivation in the liver and binding in the central nervous system means that the individual can typically drink two to five cups of coffee during the day without adverse reactions or sleep disturbances. Caffeine is normally not recommended in the evening, but individual differences prevail, as seen in most people.
- Low sensitivity to caffeine: Fast metabolizers of caffeine. Higher intakes can be consumed. Coffee drinking before bedtime does not typically disturb sleep.
"It's common for people to ask their doctor questions such as why they are kept awake by one cup of coffee, while their partner easily falls asleep after five cups," J. W. Langer, a clinical pharmacology lecturer at Copenhagen University's Medical School and lead author of the report, said in a statement. "The answer is that we are all unique coffee drinkers. Our genetic makeup programs our reaction to caffeine, just as it programs our hair color and eye color."
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Those who have a low sensitivity to caffeine will likely not experience many of the desired effects of coffee, such as wakefulness, increased concentration and alertness. However, Langer notes that people who metabolize caffeine quickly should still not exceed the recommended daily caffeine intake to try to experience these effects. The upper limit that appears to be safe for most healthy adults is 400 milligrams of caffeine a day, equivalent to around four to five cups of brewed coffee.
The report also advises that healthcare professionals should take into account the differing responses of people when advising on caffeine intake.
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