Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels.
Level 2 - randomized trial
Individual randomized double-blind crossover trial
PubMed 16204431 · doi:10.1097/01.psy.0000181270.20036.06
What was done
A double-blind crossover trial evaluated whether dietary caffeine tolerance alters salivary cortisol responses. Forty-eight men and 48 women (N = 96) completed a 4-week protocol. Each week, subjects abstained from dietary caffeine for 5 days while taking capsules totaling 0 mg, 300 mg, or 600 mg per day in three divided doses. On day 6, participants took challenge capsules of either 0 mg or 250 mg at 9:00 AM, 1:00 PM, and 6:00 PM. Salivary cortisol was measured across eight timepoints from 7:30 AM to 7:00 PM.
What was found
After 5 days of caffeine abstinence (0 mg/day), caffeine challenge doses caused a significant increase in cortisol across the day (p < .0001). Following 5 days of 300 mg/day or 600 mg/day intake, the cortisol response to the initial 9:00 AM caffeine dose was abolished. However, cortisol levels became elevated again between 1:00 PM and 7:00 PM (p = .02 to .002) following the 1:00 PM dose before declining back to control levels in the evening.
Why it matters
This study demonstrates that regular daily caffeine consumption blunts the initial morning adrenocortical response to caffeine, but tolerance is incomplete, leaving individuals susceptible to repeated cortisol elevations throughout the afternoon.
Limits
The abstract does not report baseline demographic characteristics beyond sex, nor does it report absolute cortisol concentration values or effect sizes. The 5-day adaptation period may not capture long-term habitual consumption adaptations over years, and the study tested healthy young adults without assessing downstream clinical outcomes.
Cited by
- context In chronic caffeine users, caffeine consumption does not significantly increase cortisol levels.