title: Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels.
abstract: OBJECTIVE
  Caffeine increases cortisol secretion in people at rest or undergoing mental stress. It is not known whether tolerance develops in this response with daily intake of caffeine in the diet. We therefore tested the cortisol response to caffeine challenge after controlled levels of caffeine intake.
  
  
  METHODS
  Men (N = 48) and women (N = 48) completed a double-blind, crossover trial conducted over 4 weeks. On each week, subjects abstained for 5 days from dietary caffeine and instead took capsules totaling 0 mg, 300 mg, and 600 mg/day in 3 divided doses. On day 6, they took capsules with either 0 mg or 250 mg at 9:00 AM, 1:00 PM, and 6:00 PM, and cortisol was sampled from saliva collected at 8 times from 7:30 AM to 7:00 PM.
  
  
  RESULTS
  After 5 days of caffeine abstinence, caffeine challenge doses caused a robust increase in cortisol across the test day (p < .0001). In contrast, 5 days of caffeine intake at 300 mg/day and 600 mg/day abolished the cortisol response to the initial 9:00 AM caffeine dose, although cortisol levels were again elevated between 1:00 PM and 7:00 PM (p = .02 to .002) after the second caffeine dose taken at 1:00 PM. Cortisol levels declined to control levels during the evening sampling period.
  
  
  CONCLUSIONS
  Cortisol responses to caffeine are reduced, but not eliminated, in healthy young men and women who consume caffeine on a daily basis.
authors.affiliation: Veterans Affairs Medical Center, Oklahoma City, OK 73104, USA. bill@mindbody1.org
authors.forename: William R
authors.initials: WR
authors.lastname: Lovallo
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Whitsett
authors.forename: Mustafa
authors.initials: M
authors.lastname: al'Absi
authors.forename: Bong Hee
authors.initials: BH
authors.lastname: Sung
authors.forename: Andrea S
authors.initials: AS
authors.lastname: Vincent
authors.forename: Michael F
authors.initials: MF
authors.lastname: Wilson
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D002214:Capsules; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004361:Drug Tolerance; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D010919:Placebos; D012636:Secretory Rate / Q000187:drug effects; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology*
chemical_list: D002214:Capsules; D000697:Central Nervous System Stimulants; D010919:Placebos; D002110:Caffeine; D006854:Hydrocortisone