How does coffee affect your brain and sleep if you consume it in the evening hours or shortly before going to bed?
Coffee is one of the most popular beverages in the country, with 7 in 10 Americans consuming the drink every week, according to the National Coffee Association.
While most people would probably associate coffee drinking with the daytime hours, some individuals consume the caffeinated beverage at night. This could lead to potentially negative effects when it comes to sleep quality, experts said. Caffeine is a compound found in coffee that stimulates the central nervous system.
“People often describe caffeine as speeding up the brain. Its levels peak in the blood within about 30-60 minutes of consumption,” Mary-Jon Ludy, professor of Food and Nutrition in the College of Health and Human Services at Bowling Green State University, told Newsweek. “Since the caffeine in coffee works as a stimulant, this can put the brain on high alert and make it more challenging to fall asleep.”
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When people consume coffee earlier in the day compared to in the evening, its effects on the brain have sufficient time to wear off before sleep.
The half-life of caffeine, or the amount of time that it takes for half of the stimulant effects to disappear, is about 5 hours on average, although this varies significantly between people. The half-life varies from about two hours in fast metabolizers to 10 hours in slow metabolizers.
“For example, smokers tend to process caffeine more quickly and pregnant women process caffeine more slowly,” Ludy said.
“Remember that half-life means reflects the time for half of the stimulant effects to disappear. The time for the full effects of caffeine to dissipate can be four to five half-lives. Thus, specific recommendations for timing caffeine consumption to enhance day wakefulness without harming evening sleep quality require an individualized approach.”
How does coffee affect body and brain?
Coffee has an impact on a compound known as adenosine that builds up in the body over the course of the day. Adenosine is a neurotransmitter, or chemical signal in the brain, that is involved in sleep regulation.
“The longer we are awake, the more it builds it, and then the buildup of adenosine helps us go to sleep at night,” Dr. Adrian Pristas, corporate medical director at the Hackensack Meridian Centers for Sleep Medicine, told Newsweek. “Caffeine blocks adenosine, and that is how it helps us stay awake, which is helpful in the morning, but not later in the day.”
Caffeine essentially mimics the presence of adenosine in the body, preventing brain cells from recognizing actual adenosine. Caffeine’s effects on adenosine in turn appear to trigger effects on other neurochemicals.
Caffeine is also a stimulant that increases the neurotransmitters serotonin, norepinephrine and acetylcholine in our bodies.
“All of these are awake neurotransmitters, making it hard to fall asleep,” Pristas said. “Caffeine also increases dopamine that is why coffee makes us feel better in the morning. Dopamine gives us a better mood, but could also prevent us from sleeping at night.”
In addition, caffeine suppresses melatonin—an important hormone that regulates our sleep-wake cycle.
“This is one key way caffeine can disrupt your normal sleep-wake cycle,” Michael Breus, a clinical psychologist who is a diplomate of the American Board of Sleep Medicine and a fellow of the American Academy of Sleep Medicine, told Newsweek.
“It might surprise you to hear, but caffeine has an even stronger influence on melatonin suppression than bright light. This is also an important way caffeine affects your sleep-wake cycle.”
How does coffee before bed affect sleep?
Studies have shown that caffeine affects sleep onset, extending it significantly, but this is usually based on how close to bedtime it is ingested and how much, Breus said. In addition, caffeine keeps your brain—when it finally does fall asleep—in the lighter stages of sleep.
Due to large variability in caffeine sensitivity, some people might experience severe insomnia if they drink coffee before bed, while others might report that their slumber is unaffected.
“Some of this relates to their innate sensitivity to caffeine, along with a component of tolerance to caffeine with regular consumption,” Dr. Matthew Epstein, associate medical director of the Atlantic Health System Sleep Centers and a fellow of the American Academy of Sleep Medicine, told Newsweek.
But according to the experts Newsweek spoke to, it is likely, in many cases, that the compound is still having some effect in people who drink coffee at night, even if they do not report any significant sleep problems.
“There may still be subtle effects from the caffeine, such as having brief awakenings during the night,” Epstein said. “A study several years ago actually demonstrated subtle disturbances in brainwave activity during overnight sleep following caffeine consumption from the previous morning.”
Pristas added: “Caffeine is still impacting the caffeine drinker’s body and in many cases these people are likely not sleeping as well as they think.”
According to Breus, one of three things could be going on in cases in which people drink caffeine before bed and do not experience notable sleep issues.
“One, they are so sleep deprived, that their brain is overriding the excitatory effects, so quantity might be fine, but quality is almost always off,” he said. “Two, they may not have the gene that expresses the enzyme to digest it, so it just passes through. Three, their body is so addicted that without it they go through caffeine withdrawals and that keeps them awake.”
In addition, Ludy said that people are not always great judges of their sleep quality.
“Subtle effects of poor sleep, like reduced reaction time and increased irritability, can go undetected,” he said. “It’s important for people to know that good sleep is about both the number of hours in bed and the quality of those hours. Caffeine should not be a substitute for sleep.”
Caffeine recommendations for better sleep
For people who want to avoid caffeine having an impact on their sleep, Ludy said a good rule of thumb is to avoid coffee in the six hours before bed—although this will vary between people. Switching to a decaffeinated or half-caff blend can help.
But Pristas and Breus would go further, recommending that no caffeine should be consumed after about noon for its effects to significantly wear off before bedtime.
“Since coffee has a half-life of five hours only half of the caffeine consumed is out of your body after five hours. If you have it after lunch it could affect you for another 12 to 18 hours,” Pristas said. “To get a good night’s sleep people should limit their caffeine/coffee intake to 20-24 ounces a day and finish all caffeine before noon time.”