Discover how caffeine consumption, particularly in the evening, can impact your sleep quality by reducing restorative slow-wave activity, even if you achieve a normal sleep duration, according to a new study.
A study has found that consuming caffeine in the evening may not always lead to less sleep or difficulty falling asleep, but can often affect the quality of sleep during the night.
Researchers, including those from Poland's Wroclaw Medical University, said electroencephalography (EEG), by which brain's electrical activity is recorded, makes it possible to observe sleep duration or moments of awakening, as well as the biological quality of sleep itself.
"EEG allows us to see not only whether a person is sleeping, but also how the brain is sleeping," Donata Kurpas from the department of nursing, Wroclaw Medical University and author of the study published in the journal Nutrients, said.
"Classical sleep assessment assesses sleep duration and its stages, whereas quantitative EEG analysis reveals more subtle changes, such as reduced slow-wave activity, which is an important marker of sleep depth and its restorative character," Kurpas said.
Slow waves are a key component of deep sleep -- the phase responsible for bodily regeneration, restoration of energy resources, and proper brain function.
"Caffeine may shorten sleep or make it more difficult to fall asleep; however, even when sleep duration appears normal, it may reduce slow-wave activity and shift the EEG pattern toward a more 'wakeful' brain," Kurpas said.
Thirty two studies that looked at caffeine exposure and sleep-related EEG outcomes were analysed.
The authors wrote, "Caffeine reliably alters the neurophysiological architecture of human sleep in a direction consistent with reduced sleep depth and weakened homeostatic recovery."
"Emerging evidence further suggests that caffeine increases EEG complexity and shifts sleep dynamics toward a more excitation-dominant state," they said.
This means the body may spend eight hours in bed, but the brain may fail to fully regenerate, the researchers said.
"The subjective feeling of having slept well does not always correspond to what we observe in neurophysiological recordings. A person may fall asleep without major difficulty and not remember awakenings, while the brain may display fewer features of deep sleep," Kurpas said.
Kurpas added that caffeine is neither 'good' nor 'bad' -- it is a biologically active substance, the effects of which depend on dosage, time of day, age, lifestyle, sleep quality, stress burden, and individual sensitivity.