Different Ways Caffeine Affects Sleep

The same caffeine that helps people stay focused during the day also makes it harder for them to fully rest at night.

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For many people, the day doesn’t officially begin until their first cup of coffee or tea.

A systematic review published in Nutrients found that caffeine consistently helped the brain stay focused and sped up the processing of important information. Its effects were small and inconsistent for those who were well-rested, with the greatest benefits seen when people were fatigued, needed to focus, or had much to do.

However, the same caffeine that helped people stay focused during the day also made it harder for them to fully rest at night.

The study found that caffeine reduced brain activity associated with deep, restorative sleep while increasing activity linked to having a more awake brain. These effects were especially prominent during the first few hours of sleep, when restorative sleep normally occurs.

Caffeine works by blocking adenosine from binding to its receptors. As we stay awake, adenosine gradually builds up in the brain, making us feel sleepy and increasing the brain’s drive for deep, restorative sleep. Adenosine also reduces the activity of neurons that promote wakefulness. However, when caffeine blocks adenosine receptors, it counteracts these signals, reducing the brain’s drive to enter restorative sleep and keeping it vigilant.

Some People Are More Susceptible

Depending on a person’s metabolism, genetics, age, and whether it is consumed regularly, caffeine’s effects can vary.

Adolescents may be more susceptible to the effects of caffeine. Teenagers who drank about 80 mg of caffeine—approximately the amount in a small energy drink —four hours before bedtime experienced significantly reduced deep, restorative sleep.

Researchers have found that caffeine and its metabolites, which also promote wakefulness, can persist in the body for more than 8 to 10 hours. One study mentioned in the review found that 200 mg of caffeine consumed just 10 minutes after waking altered sleep-related brain activity.

Researchers of the review suggested that caffeine’s persistence in the body may be especially relevant for people who drink caffeine throughout the day, since repeated caffeine intake can keep both caffeine and its metabolite levels elevated into the night.

While many users felt they had developed tolerance and reported little or no disruption to their sleep, EEG recordings often told a different story, revealing signs of lighter, less restorative sleep. In other words, how well we think we slept may not always match what is happening in the sleeping brain.

Additionally, people with certain variations in the ADORA2A gene, which encodes one of the brain’s adenosine receptors, have been linked to greater caffeine sensitivity and more sleep complaints.

Researchers noted that their review was not intended to advise people to avoid caffeine altogether. Instead, they suggested that people should be mindful of both when and how much caffeine they consume, as these factors may influence sleep.