Caffeine competes with the sleep pressure signal chemical called adenosine in the brain, keeping us awake and alert. It latches onto adenosine receptors without activating them, preventing us from feeling drowsy.
Caffeine can exacerbate feelings of physiological anxiety, which can lead to disrupted sleep patterns. This is due to caffeine blocking the signal of adenosine, which is important in regulating sleep.
Drinking a single cup of coffee in the evening can reduce deep sleep by about 30%, which can have the same effect on deep sleep as aging by 12-14 years. A standardized dose of caffeine can decimate deep non-REM sleep, particularly in the first two hours of the night.