Why does drinking coffee make us feel less sleepy? And when should we drink it so it doesnt affect sleep?

Coffee helps reduce sleepiness because of caffeine, a stimulant that blocks the action of adenosine, a substance that makes us feel sleepy.

First, lets get to know adenosine.

Adenosine: the sleep signal in the human brain

Adenosine is an organic compound that naturally occurs in the human body and most living organisms. It is an essential component of DNA and RNA and plays an important role in many biochemical processes.

Main properties and functions of adenosine:

Energy source
Adenosine is a core component of adenosine triphosphate (ATP), the molecule responsible for storing and transferring energy within cells.
Neural signaling
Adenosine functions as a neurotransmitter and neuromodulator in the central nervous system. When adenosine levels in the brain increase (especially after long periods of wakefulness), it triggers sleepiness and the need for rest.
Heart function
Adenosine plays an important role in regulating blood flow to the heart and is commonly used medically to treat certain types of abnormal rapid heart rhythms by slowing electrical conduction and restoring normal heart rhythm.
Blood vessel function
Adenosine helps dilate blood vessels (vasodilation), increasing blood flow to tissues.
In summary, adenosine is a critically important molecule for basic bodily functions, including energy regulation, sleep, and cardiovascular function. It is a natural substance produced continuously throughout the day.

The more energy we useintense thinking, heavy work, staying up late, or insufficient restthe more adenosine accumulates.

When adenosine binds to receptors in the brain (Adenosine receptors: A1, A2A), we feel sleepy, sluggish, less alert, and experience reduced concentration.

Therefore, adenosine regulates the bodys sleepwake rhythm by signaling that it is time to rest.

Heart rate slows slightly, blood pressure decreases a bit, and nervous system stimulation is reduced, guiding the body into rest mode.

What happens during sleep?

When we sleep, adenosine is cleared out.

During sleep, the brain gradually breaks down adenosine.
If sleep is deep enough, adenosine levels drop significantly, and we wake up feeling refreshed.
If sleep is shallow or insufficient, adenosine levels remain high, causing grogginess, drowsiness, and a heavy-headed feeling upon waking.
This is why sleep quality is more important than just the number of hours slept.

Caffeine = a fake key

Caffeines structure is similar enough to adenosine that it can bind to adenosine receptors in the brainbut without causing sleepiness like adenosine does.

The result:

Adenosine cannot bind to its receptors
Sleep signals are blocked
The central nervous system becomes more alert
Neural signaling speeds up
This is why 1015 minutes after drinking coffee, we feel more awake, clear-headed, and able to think faster.

Once sleep receptors are blocked, the body increases other important substances, such as:

Dopamine improves mood
Adrenaline increases alertness
This is why coffee is not just an anti-sleep drink, but also a drink that can enhance work performance.

Why do some people feel fine after coffee, while others experience palpitations or insomnia?

Because genetics differ from person to person, the ability to metabolize caffeine also varies.

Caffeine is metabolized by the enzyme CYP1A2, which functions at different levels in different individuals.

Fast metabolizers: can drink coffee comfortably with minimal side effects
Slow metabolizers: caffeine remains in the body longer, causing palpitations, restlessness, and difficulty sleeping
This is why the appropriate amount of coffee differs for each person.

The half-life of caffeine is approximately 46 hours. Even if coffee is consumed in the morning, 3040% of caffeine may still remain in the body before bedtime. Therefore, drinking coffee after 4:00 PM can leave enough residual caffeine to delay sleep onset or reduce sleep depth for some people.

Pros and cons of caffeine

Benefits (when consumed in appropriate amounts):

• Improves brain performance: alertness and memory increase by about 1015%, supported by multiple studies
• Slightly boosts metabolism Provides antioxidants from coffee
• Reduces the risk of certain diseases, such as Parkinsons and Alzheimers (supported by long-term studies)

Drawbacks (when consumed excessively):

• Palpitations, anxiety, difficulty sleeping
• Increased stomach acid
• Dependence on caffeine, leading to increased sleepiness when not consumed
• Drinking in the Afternoon or evening consumption worsens sleep quality, even if sleep still occurs

Healthy coffee-drinking guidelines

• Drink between 9:0011:00 AM, when cortisol levels decline and caffeine is more effective
• Avoid drinking after 3:00 PM
• Avoid drinking on an empty stomach, especially for those with sensitive stomachs; pair with a small snack or fruit

Recommended daily intake: 200300 mg of caffeine

(approximately 12 cups, not exceeding 3 cups of coffee per day)

Although coffee can help boost productivity and energy, drinking it after mid-afternoon should be approached with caution due to its impact on sleep quality. When it is time to rest, the body should be allowed to recover fully for good health.