Caffeine metabolism: Why effects vary between individuals

The varying effects of caffeine on alertness and sleep are primarily driven by how individual bodies metabolize the substance. Caffeine does not provide additional energy; instead, it masks fatigue by blocking adenosine, a compound in the brain that signals sleepiness.

Metabolism rates can vary significantly, with the process of breaking down and eliminating caffeine lasting between six and 20 hours. A key factor in this variation is the CYP1A2 gene, which controls the liver enzyme responsible for decomposing caffeine. Other lifestyle and biological factors also play a role: smoking can accelerate caffeine elimination by up to 65%, while pregnancy, certain antibiotics, and oral contraceptives can prolong its effects.

Experts suggest that regular consumers may develop a tolerance, while those who consume caffeine late in the day may experience anxiety or sleep disruption due to accumulated levels. Health organizations, such as the NHS, recommend specific limits for certain groups, such as pregnant women, to avoid complications.