According to a report by physician, author, and media commentator J.W. Langer, sensitivity to caffeine is a result of the genetic variability in liver metabolism and central nervous system sensitivity. He breaks up overall caffeine sensitivity into three major groups.
High
High sensitivity to caffeine is due to slow-metabolism in the liver and high binding in the central nervous system. This means that even a small amount of caffeine will be effective in causing stimulation. In some cases, higher doses of caffeine may cause sleep problems
Regular
In this instance, the individual has a balance between caffeine inactivation in the liver and binding in the central nervous system. They can typically drink 2–5 cups of coffee during the day but without adverse reactions or sleep disturbances.
Low
These individuals are fast-metabolizers of caffeine. They are able to intake higher amounts of caffeine – although to maintain a healthy lifestyle, consider staying within the EFSA guidelines of no more than 5 cups of coffee per day.
Each individual is different in how they manage their own caffeine intake to suit their personal lifestyle. At the same time, "It is likely that people who are more sensitive to caffeine will self-moderate their intake based on what they know they can tolerate," said Langer in his report.
