"Two of the genes which are thought to have the largest impact are CYP1A2 and ADORA2A. Caffeine metabolism is mainly determined by the cytochrome enzyme P-450 1A2 (CYP1A2)," Clarke said.

Specifically, caffeine sensitivity depends partly on a liver enzyme called CYP1A2, which is coded by the CYP1A2 gene. The enzyme is responsible for "inactivating 95 percent of all ingested ...

The researchers say it is all about the speed at which a person metabolizes caffeine. In the study, about half of the participants had the rs762551 variant of the CYP1A2 gene, a variant that ...

The study looked at 604 participants aged 18 to 45, regularly assessed over a 7.5-year follow-up period for 16 years. About half of the participants had the CYP1A2 gene variant.