February 13, 2026, 3:20 pm | Read time: 4 minutes
Many people still drink coffee late in the afternoon and later wonder why they can’t relax in bed. The disruptive influence of caffeine on sleep goes beyond just falling asleep. FITBOOK editor-in-chief Nuno Alves is deeply engaged with topics like healthy aging, which includes sleep. His book, “Highway to Health – 7 Steps for a Healthy Long Life”, set to be released in January, also covers this topic. Here, he explains how coffee works and when it’s best to have your last cup of the day.
Sleep is one of the central pillars for health and performance. It strengthens the immune system and regulates metabolism. During the night, the brain’s glymphatic system breaks down cellular waste, including proteins like beta-amyloid, suspected of promoting neurodegenerative diseases such as dementia. This mechanism likely contributes to protecting cognitive health. Sleep also triggers what should interest athletes: the release of growth hormones essential for cell repair, muscle regeneration, and muscle mass building. Poor or insufficient sleep can even promote muscle breakdown—something few would desire.
Despite the importance of restful sleep, many still reach for coffee in the afternoon. I see this regularly in the office: While I prefer to consider a calming tea around 5 p.m., some colleagues quickly grab an espresso or a cup of filter coffee. I used to do the same—and then regularly stayed awake well past midnight. In hindsight, it’s no surprise that the sleep was rarely restful.
How Long Caffeine Stays in the Body
Caffeine is stimulating because it blocks the receptors for the neurotransmitter adenosine in the brain—the molecule that signals fatigue. Adenosine typically accumulates throughout the day as it forms during energy consumption in the brain. When it binds to specific sites in nerve cells, brain activity slows down, making us tired. However, if these receptors are blocked by caffeine, adenosine cannot exert its effect.
But how long does caffeine affect the body? This is referred to as the half-life. While it can vary greatly, the average is about five hours.1 In exceptional cases, it can be less or more. Assuming the average: If you drink a cup of coffee at 5 p.m. containing about 100 milligrams of caffeine, you’ll still have about half of it in your blood by 10 p.m. And 50 milligrams is significant, considering an espresso contains approximately 70 milligrams of caffeine.
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How Caffeine Changes Sleep–Even When You Think You’re Sleeping Well
How Caffeine Affects Sleep
The physiological effects of caffeine on sleep are well-documented. A 2023 meta-analysis of 24 studies showed that the natural alkaloid on average …
- reduces sleep efficiency by 7 percent
- shortens total sleep duration by 45 minutes
- extends the time it takes to fall asleep by 9 minutes
- lengthens wake phases by 12 minutes
- increases light sleep proportionally by 1.7 percent
- reduces deep sleep by 1.4 percent 2
As we can see, caffeine alters our sleep. The study authors therefore recommend drinking the last cup of coffee with around 100 milligrams about nine hours before going to bed. If you consume double the amount, you should increase the interval to 13 hours.
Also interesting: Does coffee before exercise enhance performance?
I Drink My Last Coffee by 9:30 a.m. at the Latest
I also used to regularly drink coffee until about 6 p.m., convinced it had no impact on my sleep. But the truth is, without late caffeine, I usually woke up more refreshed the next morning. My smart ring confirmed the observation. Nowadays, I try to have my last coffee by 9:30 a.m. at the latest. After that, I stick to water or tea.
Many are surely convinced they can handle a late coffee relatively well. But statistically, the likelihood that they are fast metabolizers of caffeine is extremely low.