Experts Say Caffeine Can Linger 20 Hours, Driving Wide Sensitivity Gaps
Updated
Updated · bbc.co.uk · Sep 17
Experts Say Caffeine Can Linger 20 Hours, Driving Wide Sensitivity Gaps
1 articles · Updated · bbc.co.uk · Sep 17
Summary
Caffeine can stay in the body for 6 to 20 hours, experts said, helping explain why one person can sleep after coffee while another feels anxious or lies awake.
The difference starts with metabolism: the liver enzyme tied to the CYP1A2 gene breaks caffeine down at different speeds, with one recent study finding Europeans and South Americans tend to process it faster on average.
Smoking can speed caffeine clearance by as much as 65%, while some antibiotics, contraceptive pills and pregnancy can slow it, leaving the stimulant active for longer.
Regular use also changes the response, as tolerance can blunt caffeine's effects and then fade after a few weeks without it, making the next cup feel unusually strong.
Sleep experts often advise avoiding caffeine at least 6 hours before bed—around 2 p.m. for a 10 p.m. bedtime—while the NHS tells pregnant women to stay below 200mg a day.