Caffeine and Cortisol: No Full Tolerance

You've had coffee daily for thirty years, so surely it does nothing to you now. Partly true. Not entirely.

What the researchers actually did

Lovallo and colleagues administered caffeine and placebo to habitual coffee drinkers under controlled conditions across the day, measuring salivary cortisol responses at morning, afternoon and evening timepoints.

What they found

• Caffeine raised cortisol even in people who drink it every day.
• Tolerance to the cortisol effect was incomplete.
• The effect was most pronounced in the afternoon.
• Morning caffeine, taken after the natural rise, was the least disruptive timing.

What it means for you

You do not have to quit coffee. You have to move it. Caffeine before your own morning rise blunts it; caffeine after 2 PM props up the part of the curve that should be falling.

What to do with it this week

• Delay the first cup 60–90 minutes after waking.
• Set a hard caffeine cutoff at 2 PM, including tea and diet soda.
• Swap the 3 PM cup for the five-minute walk.
• Give it a week before deciding it doesn't matter.