title: Caffeine increases tear volume depending on polymorphisms within the adenosine A2a receptor gene and cytochrome P450 1A2.
abstract: OBJECTIVE
  The primary aim of the present study was to examine the effect of caffeine on tear volume. The secondary aim was to investigate the relation between caffeine-induced changes in tear volume and polymorphisms in ADORA2A and CYP1A2.
  
  
  METHODS
  Double-masked, placebo-controlled, crossover study.
  
  
  METHODS
  Seventy-eight healthy volunteers were recruited for the study.
  
  
  METHODS
  Subjects participated in 2 sessions in which they received capsules containing either placebo or caffeine. The caffeine capsules were given to the subjects to keep the caffeine volume per body weight within 5 to 7 mg/kg. After caffeine intake, tear meniscus height (TMH) was measured. Subjects provided a blood sample for genotyping.
  
  
  METHODS
  Tear meniscus height, single nucleotide polymorphism.
  
  
  RESULTS
  The tear volume increased after caffeine consumption. The net increase in TMH was 0.08 mm (95% confidence interval, 0.05-0.10) greater when participants were given caffeine than when given placebo (P<0.0001). In ADORA2A, the difference in the net increase in TMH for participants who were heterozygous at rs5751876 and rs2298383 was 0.07 mm (P = 0.001) and who were minor homozygous was 0.08 mm (P = 0.007). In CYP1A2, the net increase in TMH for participants who were minor homozygous at rs2472304 was lower than for those who were major homozygous; the difference was 0.06 mm (P = 0.039).
  
  
  CONCLUSIONS
  Caffeine intake increases tear volume and polymorphisms within ADORA2A, and CYP1A2 is associated with the tear increase after caffeine intake. Genetic polymorphisms had a significant effect on tear meniscus that was of limited clinical significance.
authors.affiliation: Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan. ritoh@za2.so-net.ne.jp
authors.forename: Reiko
authors.initials: R
authors.lastname: Arita
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Yanagi
authors.forename: Norihiko
authors.initials: N
authors.lastname: Honda
authors.forename: Shuji
authors.initials: S
authors.lastname: Maeda
authors.forename: Koshi
authors.initials: K
authors.lastname: Maeda
authors.forename: Aya
authors.initials: A
authors.lastname: Kuchiba
authors.forename: Takuhiro
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Yanagihara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Shiro
authors.initials: S
authors.lastname: Amano
mesh_terms: D000328:Adult; D001824:Body Constitution; D002110:Caffeine / Q000008:administration & dosage*; D002214:Capsules; D018592:Cross-Over Studies; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics*; D004311:Double-Blind Method; D005260:Female; D060005:Genotyping Techniques; D006801:Humans; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D043705:Receptor, Adenosine A2A / Q000235:genetics*; D013666:Tears / Q000378:metabolism*; D055815:Young Adult
chemical_list: D002214:Capsules; D043705:Receptor, Adenosine A2A; D002110:Caffeine; D019388:Cytochrome P-450 CYP1A2