Why caffeine jolts some people while others feel no effect
Caffeine’s impact varies because of genetic differences, liver metabolism speed, lifestyle factors and tolerance, meaning some can drink coffee late and still sleep while others stay awake.
Caffeine works by blocking adenosine, a brain chemical that promotes sleep, but how long it affects a person hinges on how quickly the liver metabolises it. The enzyme CYP1A2, governed by a single gene, can clear caffeine in as little as six hours or as long as twenty, with average differences noted between Europeans and South Americans. Lifestyle choices matter: smokers process caffeine up to 65% faster, while some antibiotics, contraceptives and pregnancy hormones slow the process.
Habitual coffee consumers build tolerance, yet a pause can reset sensitivity, making the first cup feel intense. Sleep specialists advise avoiding caffeine several hours before sleep, but acknowledge personal variation. Overall, moderate coffee consumption is linked to lower disease risk, though excessive intake can cause jitteriness.
