You sleep eight hours, but wake up tired? What could be the cause?

Caffeine undermines the quality of sleep – a claim that may seem trivial or even self-evident, but which stems from a systematic analysis of 32 studies examining the electrical activity of the brain during sleep, as focus.it writes.

“Electroencephalography enables us not only to know whether a person is asleep, but also how their brain is sleeping,” explains Donata Kurpas, one of the authors of the study published in the journal “Nutrients”.

Less regenerative sleep

The main finding is that caffeine makes sleep less regenerative by reducing low-frequency activity during the NREM phase of sleep – specifically the slow waves that are characteristic of deep sleep.

We may not notice this consciously, since we continue to fall asleep easily at our usual time and sleep the usual number of hours without waking; nevertheless, the quality of that sleep suffers damage and we may feel less rested when we wake up.

“Caffeine can change the brain’s activity, making it more reactive and more alert,” Kurpas explains.

It affects each of us differently

Moreover, caffeine does not affect everyone in the same way: some people can drink coffee at 23:00 and sleep like a log, while if I order an espresso at a café after 14:00, I know I will have to count at least 1,200 sheep that night before finally managing to sleep.

There is also a scientific basis for this: our body’s reaction to this substance depends on different factors, such as genetics, metabolism, age, stress and chronic fatigue.

A vicious circle

Poor sleep during the night pushes us to consume more caffeine; increased caffeine consumption leads to poor sleep during the night.

“If caffeine helps us stay active during the day, but at the same time undermines the quality of our night’s rest, a vicious circle is created: greater fatigue, greater need for stimulation, and qualitatively poorer sleep,” Kurpas summarises.

Ultimately, it is not enough simply to look at how quickly we fall asleep – regardless of the coffee we have consumed – or how many hours we sleep during the night; we must shift the focus from the quantity of sleep to its quality, analysing the brain’s activity during the night and the real regenerative effectiveness of the hours spent sleeping.