"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.

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.

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 ...