One of the undeniable benefits of coffee is its power to stimulate and increase energy — it’s no wonder that it’s very popular in the morning and some people drink it throughout the day. However, it’s necessary to be mindful of consumption times to avoid disrupting sleep. A review of studies published in the journal Sleep concluded that to avoid the deleterious effects of caffeine on sleep, the last cup should be consumed 8.8 hours before going to bed.
This means that for a person who usually goes to sleep at 10 PM, the last coffee should be consumed right after lunch, around 1 PM. “This result is indeed new information,” observes neurologist Letícia Soster from the Sleep Medical Assistance Group at Albert Einstein Israelite Hospital. According to her, the current recommendation is that the last cup should be consumed, on average, six hours before bedtime. “If an individual needs to drink coffee later, there might be something happening that needs to be investigated,” warns Soster.
However, despite there being a consensus on the recommendation for the latest time to consume coffee, this doesn’t apply to the amount to be ingested. The reason, the doctor explains, is the differences in caffeine metabolism in each organism. In the study, the authors emphasize that consuming a cup of coffee close to bedtime decreases total sleep time, and this impact is greater the closer it is to bedtime.
“We don’t talk about quantity, but especially about avoiding consumption times. People are different in relation to caffeine sensitivity and there is a very large individual variation, which can even be genetically determined,” says the Einstein doctor.
More Impacts
The review of studies also brought other conclusions: caffeine consumption closer to bedtime reduces sleep time by about 45 minutes, decreases sleep efficiency by 7%, shortens deep sleep time and increases light sleep time.
“This is a big problem. Imagine reducing sleep time by 45 minutes each night. The sum of this at the end of seven days results in sleep deprivation that the person imposed due to a dietary habit,” points out Soster.
The neurologist considers that the 7% decrease in sleep efficiency is also a point of attention. For a night’s sleep to be considered healthy, it needs to have an efficiency of around 85%. “We make this calculation based on polysomnography exams. Efficiency is measured between the time the person is in bed and how much of that time they actually managed to sleep,” explains the doctor.
How Does Caffeine Act in the Body?
The substance inhibits sleep by decreasing the action of adenosine — a neurotransmitter associated with the feeling of tiredness. In a normal situation, a person wakes up, spends energy, and releases adenosine molecules, manifested as fatigue, making actions and reactions slower as the day progresses.
When caffeine is absorbed by the body, it takes the place of adenosine in the brain. “As a result, instead of adenosine acting on the brain, promoting tiredness, caffeine will act in its place, stimulating the body,” details the neurologist. The problem is that when the peak of coffee’s action decreases, the person will feel the accumulated fatigue all at once, worsening the sensation and possibly consuming more coffee.
According to Soster, the recommendations of the new study are more restrictive than those usually used, but the results are important for people to try to understand why they drink coffee more often and later to stay awake or be able to work. “There are other things that lead to this and coffee might be disguising it. Additionally, there’s the issue of habituation: that person’s brain is used to functioning only in this way. All of this needs to be evaluated,” she highlights.
The Importance of Sleeping Well
Quality sleep is an essential component of physical and emotional well-being. Current recommendations describe the need for healthy adults to sleep seven to nine hours per night (although this is an individual need). For many years, science has shown that insufficient sleep is a growing challenge, as it is increasingly common for people to suffer from sleep disorders.
And this is worrying for several reasons. It is during sleep that the body performs several important physical and metabolic processes for its proper functioning. But often, people give up this rest due to a “sense of urgency” to continue producing or do other things, such as watching a series or staying on the phone.
“When the body complains, the person goes and takes some stimulant. But it’s important to understand that we are not machines, our body needs rest. Poorly slept nights result in oxidative stress processes, premature aging, worsening of cardiovascular levels and glycemic indices. This is the context of the price that lack of sleep charges us in the future. We are the ones who make our choices,” says Letícia Soster.