How Caffeine Disrupts Sleep: Adenosine Blockade and Circadian Effects

Mechanism: Adenosine Receptor Antagonism

Adenosine accumulates during wakefulness, binding A₁/A₂A receptors to promote sleep pressure. Caffeine (structurally similar) competitively blocks these receptors, preventing the "tired" signal.

Downstream Effects

• ↑ Neuronal firing → ↑ dopamine, norepinephrine, glutamate
• ↑ Arousal, vigilance, cognitive throughput
• Vasoconstriction (cerebral blood flow ↓ ~20–30%)
• ↑ Heart rate, BP, gastric acid secretion

Impact on Sleep Architecture

• ↑ Sleep latency (time to fall asleep)
• ↓ Total sleep time
• ↓ Slow-wave sleep (N3) — most restorative stage
• ↓ REM sleep (especially with evening intake)
• ↑ Fragmentation, awakenings

Circadian Disruption

Caffeine delays melatonin onset and shifts circadian phase later, exacerbating delayed sleep phase tendency.

Practical Guidelines

• Half-life: 3–7 hours (highly variable: genetics, smoking, OCPs, pregnancy, liver function)
• Cutoff: 8–10 hours before bedtime for most
• Limit: ≤400 mg/day (FDA); ≤200 mg if sensitive/pregnant
• Sources: coffee (95 mg/8oz), tea (47 mg), energy drinks (70–300 mg), soda, chocolate, medications