Indeed, mutations on the CYP1A2 gene were recently shown to influence abstract reasoning in a large population (1374 participants) under free caffeine intake in everyday life [36], and genetic variations of inflammatory cytokines IL-6 and TNF-α have been associated in several studies with sleep disturbances [37] and susceptibility and severity of obstructive sleep apnea [38,39]. Here, CYP1A2 is linked to obstructive sleep apnea syndrome.