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Randomized Controlled Trial
. Sep-Oct 2005;67(5):734-9.
doi: 10.1097/01.psy.0000181270.20036.06.

Caffeine Stimulation of Cortisol Secretion Across the Waking Hours in Relation to Caffeine Intake Levels

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Free PMC article
Randomized Controlled Trial

Caffeine Stimulation of Cortisol Secretion Across the Waking Hours in Relation to Caffeine Intake Levels

William R Lovallo et al. Psychosom Med. .
Free PMC article

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.

Conclusion: Cortisol responses to caffeine are reduced, but not eliminated, in healthy young men and women who consume caffeine on a daily basis.

Figures

Figure 1
Figure 1
Caffeine concentrations in saliva on 4 test days. Entries show means, and error bars represent standard errors. Samples from 7:30 AM to 2:00 PM were collected in the laboratory, and the samples at 6:00 and 7:00 PM were collected at home. PC = placebo maintenance followed by 3 × 250-mg caffeine challenges on the test day. C300 = 300 mg/day of caffeine at home followed by caffeine challenge on the test day. C600 = 600 mg/day at home followed by caffeine challenge on the test day. PP = placebo at home and placebo on test day. Base 1, Base 2, Base 3 = saliva samples taken immediately before taking a caffeine or placebo capsule. PostC = samples taken 1 hour postdrug. Stress and Recov = samples taken at the end of a 30-minute behavioral stress period or after 30 minutes of recovery.
Figure 2
Figure 2
Cortisol concentrations in saliva on 4 test days. Entries show means and standard errors. Abbreviations, sampling times, and designations as in Figure 1. Numbers above error bars refer from top to bottom to p values of PC, C300, and C600 week contrasts against the PP week control value.

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