title: Subjective and objective effects of coffee consumption - caffeine or expectations?
abstract: Impact of 5 mg/kg caffeine, chance of receiving caffeine (stimulus expectancies), and expectations of effects of caffeine (response expectancies) on objective (heart rate (HR), systolic/diastolic blood pressure (SBP/DBP), measures of heart rate variability (HRV), and reaction time (RT)) and subjective variables were investigated in a double-blind, placebo-controlled experiment with a no-treatment group. Participants were 107 undergraduate university students (mean age 22.3 ± 3.96 years). Consumption of 5 mg/kg caffeine had an impact on participants' SBP, standard deviation of normal heartbeat intervals, HR (decrease), and subjective experience 40 minutes later even after controlling for respective baseline values, stimulus and response expectancies, and habitual caffeine consumption. No effects on DBP, high frequency component of HRV, the ratio of low- and high-frequency, and RT were found. Beyond actual caffeine intake, response expectancy score was also a determinant of subjective experience which refers to a placebo component in the total effect. Actual autonomic (SBP, HR) changes and somatosensory amplification tendency, however, had no significant impact on subjective experience. Placebo reaction plays a role in the subjective changes caused by caffeine consumption but it has no impact on objective variables. Conditional vs deceptive administration of caffeine (i.e. stimulus expectancies) had no impact on any assessed variable.
authors.affiliation: Eötvös Loránd University Department of Physiology and Neurobiology Budapest Hungary.
authors.forename: Zs
authors.initials: Z
authors.lastname: Dömötör
authors.affiliation: Eötvös Loránd University Institute for Health Promotion and Sport Sciences Bogdánfy Ödön u. 10 H-1117 Budapest Hungary.
authors.forename: R
authors.initials: R
authors.lastname: Szemerszky
authors.affiliation: Eötvös Loránd University Institute for Health Promotion and Sport Sciences Bogdánfy Ödön u. 10 H-1117 Budapest Hungary.
authors.forename: F
authors.initials: F
authors.lastname: Köteles
mesh_terms: D000284:Administration, Oral; D000339:Affect / Q000187:drug effects / Q000502:physiology*; D059031:Anticipation, Psychological / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D002110:Caffeine / Q000008:administration & dosage*; D003069:Coffee / Q000737:chemistry*; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D015990:Placebo Effect; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
chemical_list: D003069:Coffee; D002110:Caffeine
keywords: blood pressure; caffeine; double-blind versus deceptive administration; expectations; heart rate; heart rate variability; placebo