Can caffeine delay sleep onset and reduce deep sleep, with CYP1A2 rs762551 AC possibly prolonging exposure?

Caffeine’s sleep effects are well established, whereas using CYP1A2 rs762551 AC alone to predict an individual’s caffeine persistence is less certain.

Clinical sleep effects

• In a 2025 meta-analysis of 22 controlled crossover trials (956 healthy adults), caffeine increased sleep-onset latency by 8.35 minutes versus placebo and reduced slow-wave sleep—the objective correlate of deep sleep—by 1.01 percentage points.
• Effects depend substantially on dose and timing. In randomized double-blind crossover evidence, 400 mg delayed sleep onset when taken within 12 hours of bedtime and reduced slow-wave sleep when taken at bedtime or 6 hours before bed. In that study, 100 mg did not significantly affect sleep at the intervals tested.
• Caffeine can also increase sleep fragmentation, particularly when 400 mg is consumed within 8 hours of bedtime.

Mechanism

• At usual dietary exposures, caffeine competitively antagonizes adenosine A₁ and A₂A receptors. Adenosine signaling normally contributes to the accumulation of sleep pressure during wakefulness; blocking these receptors plausibly sustains alertness while attenuating sleep-homeostatic slow-wave activity.

CYP1A2 genotype and exposure

• rs762551 AC is plausibly associated with intermediate, or relatively slower-than-AA, caffeine clearance. The A allele is linked to greater CYP1A2 inducibility, especially under inducing conditions, rather than a fixed clearance rate.
• Slower clearance can extend caffeine’s concentration-time profile, but AC does not provide a validated individual half-life, AUC, or clearance estimate. Smoking can induce CYP1A2 and increase clearance, while oral contraceptives inhibit it and reduce clearance; habitual intake and other factors also matter.

Bottom line

• Caffeine can delay sleep onset, reduce deep sleep, and fragment sleep, especially at higher doses later in the day. AC genotype may contribute to prolonged exposure, but it should not be used alone to predict personal caffeine sensitivity or timing.