Caffeine sensitivity refers to how the body processes caffeine, due, in large part, to genetics.
Caffeine tolerance describes how the body responds to caffeine over time. A tolerance develops when the desired effects of caffeine eventually decrease with regular consumption.
Your sensitivity can be determined by:
Liver Metabolism Caffeine is metabolized (broken down) in the liver by an enzyme (protein) known as CYP1A2. The gene associated with this enzyme helps predetermine how sensitive a person may be to caffeine consumption. Studies have found people with a high caffeine sensitivity don't produce as much CYP1A2.
Medications Some medications and supplements can interact with caffeine sensitivity.
Genetics Research has shown that a person's genetic makeup has a lot to do with how they respond to caffeine.
In addition to the CYP1A2 gene that influences how quickly the liver breaks down caffeine, another gene known as ADORA2A impacts how the central nervous system (communication between the brain and body) reacts to caffeine's stimulating effects. People who have a variation of the ADORA2A gene are likely to have a high sensitivity to caffeine that affects their sleeping pattern.