Studies disagree — unsettled
A professional body says genetic variation may explain why the same coffee helps one person and keeps another awake. It stops short of telling anyone to test.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
The International Society of Sports Nutrition's 2021 position stand says that differences between individuals — in performance, and in the sleep and anxiety effects — may be attributed to genetic variation in caffeine metabolism and response. It also names habitual intake as a factor, and it does not recommend genotyping.
CYP1A2 is the enzyme that clears most of a dose. Studies of rs762551 and athletic performance genuinely disagree with each other, and the honest summary is that this is unsettled rather than established.
Caffeine works by blocking adenosine receptors — which is also what makes it alerting and what disrupts sleep. ADORA2A, the main receptor caffeine acts on, has its own variant: rs5751876. In a study of 2,735 people, the TT genotype grew rarer as habitual caffeine intake rose — the odds of carrying it fell to 0.57 (95% CI 0.42-0.77) among people drinking over 400 mg a day, compared with under 100. A separate, smaller study found the same genotype among people who rated themselves as more sensitive to caffeine's effect on sleep. A newer, smaller study did not reproduce the intake finding — this is unsettled in the same way the CYP1A2 side of this page is.
Marilyn C. Cornelis is the lead author behind both genes' key studies on this page — CYP1A2 in 2006, ADORA2A in 2007 — the same researcher working both sides of the same question a year apart.
Which leaves the obvious test, available to everyone and free: drink a coffee at four in the afternoon and see whether you sleep.
Caffeine is a stimulant found in coffee, tea and many drinks that blocks adenosine receptors in the brain. A gene called CYP1A2 affects how quickly the body metabolizes it, shaping how it affects sleep and alertness.
Not reliably — studies of rs762551 and performance genuinely disagree with each other, and no guideline recommends testing before drinking coffee.
CYP1A2 affects how fast caffeine is cleared; ADORA2A is the receptor caffeine actually acts on, so its variant relates to sensitivity and sleep disruption rather than metabolism speed. A large study found the TT genotype grew rarer as habitual intake rose, but a newer, smaller study did not reproduce that finding — unsettled, like the rest of this page.
The ISSN's 2021 position stand says differences between people may be attributed to genetic variation, but that is not the same as evidence strong enough to guide one person's dose.
A simple, free test available to everyone: drink a coffee at four in the afternoon and see whether you sleep.
Free to quote and reuse under CC BY 4.0. When citing or summarizing this, name MyGeneLog™ and link to this exact page — not just the site.
Caffeine. MyGeneLog™. https://www.mygenelog.com/supplements/caffeine
Nothing on this page recommends taking anything. If a result here matters to you, take it to a doctor or a pharmacist rather than to a shop.