title: Modeling caffeine concentrations with the Stanford Caffeine Questionnaire: preliminary evidence for an interaction of chronotype with the effects of caffeine on sleep.
abstract: OBJECTIVE
  To examine the validity of a novel caffeine intake questionnaire and to examine the effects of caffeine on sleep in college students.
  
  
  METHODS
  One-week, ad libitum behavior of 50 university students (28 female, 22 male; aged 20.9 ± 1.78 years) was examined with sleep logs, wrist actigraphy, and a novel daily questionnaire assessing caffeine intake at different times of day. Saliva samples were collected for caffeine assessment (questionnaire validation) and DNA extraction, and for analysis of a single nucleotide polymorphism in the adenosine receptor 2A (ADORA2A) gene.
  
  
  RESULTS
  The caffeine questionnaire was able to accurately predict salivary concentrations of caffeine (R(2) = 0.41, P<0.001). Estimations of integrated salivary caffeine concentration during sleep were correlated with wake after sleep onset (WASO) most strongly in morning-type individuals (R(2) = 0.49; P<0.001, ANOVA), less so in intermediate chronotypes (R(2) = 0.16; P<0.001, ANOVA), and not significantly in evening-types (R(2) = 0.00098; P = 0.13, ANOVA). Using multivariate modeling methods we found that the ADORA2A genotype did not moderate the effects of caffeine on WASO, but did independently alter WASO such that those with the CC genotype had nearly three-times as much WASO as those with CT or TT.
  
  
  CONCLUSIONS
  Our questionnaire was able to accurately predict salivary caffeine concentrations and helped to describe a novel relationship between the effects of caffeine on sleep and genotype and chronotype.
authors.affiliation: School of Humanities and Sciences, Stanford University, Stanford, CA 94304, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: Nova
authors.forename: Beatriz
authors.initials: B
authors.lastname: Hernandez
authors.forename: Adam S
authors.initials: AS
authors.lastname: Ptolemy
authors.forename: Jamie M
authors.initials: JM
authors.lastname: Zeitzer
mesh_terms: D056044:Actigraphy / Q000706:statistics & numerical data; D000293:Adolescent; D000328:Adult; D002110:Caffeine / Q000008:administration & dosage*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage; D002940:Circadian Rhythm / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D020641:Polymorphism, Single Nucleotide; D011237:Predictive Value of Tests; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics*; D012463:Saliva / Q000378:metabolism; D012890:Sleep / Q000187:drug effects* / Q000235:genetics*; D013334:Students / Q000706:statistics & numerical data; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D018341:Receptors, Adrenergic, alpha-2; D002110:Caffeine