The widely accepted advice to avoid coffee after 2pm masks a far more nuanced biological reality. A systematic review of 141 pharmacokinetic studies reveals that caffeine metabolism varies dramatically across individuals—with a 15- to 40-fold difference in clearance rates among healthy adults. This variability stems from genetic differences in the CYP1A2 enzyme, which metabolizes approximately 95% of consumed caffeine, combined with significant lifestyle and physiological factors. The same cup of coffee that leaves one person alert at midnight may already be cleared from another’s system by early evening. Rather than adhering to population-based timing rules, the research suggests a more personalized approach to caffeine consumption that accounts for individual metabolic profiles, smoking status, contraceptive use, and pregnancy status. Understanding your own caffeine sensitivity offers a more scientifically grounded path to better sleep quality.
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