Caffeine that was given to people 3 hours before normal bedtime caused a 40-minute shift in the body’s internal clock, about half of what 3 hours of bright light exposure at night did.

Chronic caffeine exposure caused a lengthening of the circadian clock in human cells (in-vitro) via changing adenosine receptor signaling.

These data suggest that in addition to increasing daytime exposure to bright light and reducing evening exposure to blue light, avoiding caffeine later in the day may be important to improve sleep latency.