How can some people drink five cups of coffee a day without ascending to another plane while others just need a whiff of espresso to send their bodies into a buzz? Genetics play a huge role, according to a new report by Dr. JW Langer, which breaks caffeine imbibers into three sensitivity groups.
The report, published last week, explains the role one enzyme, called "CYP1A2", plays in how our bodies handle caffeine:
[One enzyme] is responsible for inactivating 95% of all ingested caffeine. The ability to produce this enzyme is coded for by the CYP1A2-gene. Different people have different versions of the CYP1A2-gene, and these genetic variations determine how active the CYP1A2-enzyme is in each person.
Essentially, you can have a "very active" (where caffeine is metabolised quickly) or "less active" (more slower) version, or something in between, which means most of us can be separated into three groups: high, regular and low sensitivity.
If you're on the high end, you can have five or more cups of coffee (a cup in this case holding a 100mL of caffeine) without being overly stimulated, to the point where a cappuccino nightcap won't "typically disturb sleep".
Regular drinks can handle between two to five, though bedtime coffees aren't recommended.
Finally, for the low sensitivity group, where caffeine is metabolised slowly... well, best take a sip of someone else's brew (or stick to a splash of cold water):
Slow-metabolism in the liver and high 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.
You can definitely build a tolerance to caffeine, but if you find it difficult to get started on a single cup — or can communicate with aliens by licking the inside of a portafilter — you might just have to blame it on genetics.
Genetics, metabolism and individual responses to caffeine [Coffee & Health, via Live Science]