The key facts
- Cardiologist Marcos Cairo recommends the last cup of coffee 6–8 hours before sleep
- The half-life of caffeine averages 5–6 hours
- The effect depends on dose, sensitivity, age, and metabolism
Recommendation on the timing of coffee consumption
Cardiologist Marcos Cairo, in a conversation with the Brazilian outlet Metropoles, said that coffee consumption in the afternoon can impair the quality of nighttime sleep. To reduce caffeine's impact on the body, he advised having the last cup of the drink six to eight hours before going to bed.
How caffeine affects the body
According to the doctor, the half-life of caffeine averages about five to six hours: during this time the body processes roughly half of the ingested substance, while the remaining part continues to act. “For example, if you drink coffee at 4:00 PM, by 10:00 PM about half of the original dose of caffeine may still remain in the body. As a result, it can be harder for a person to fall asleep, and sleep itself may become shallower and more interrupted,” Cairo explained. Caffeine stimulates the central nervous system by blocking adenosine receptors. Adenosine accumulates during the day and participates in forming the natural feeling of sleepiness; when caffeine prevents its action, the sensation of fatigue is temporarily weakened, although the body's need for sleep remains.
Individual differences
Scientific studies show that caffeine can increase the time it takes to fall asleep, reduce total sleep duration, and lower sleep efficiency. The severity of the effect depends on the dose, individual sensitivity, age, metabolic characteristics, and medications being taken. The half-life of caffeine in some people is significantly longer than average, so the recommendation to avoid coffee six to eight hours before sleep is a guideline rather than a universal rule.
