Caffeine: To drink or not to drink? The ongoing scientific debate on the benefits and harms of this substance consumed by millions of people every day seems never-ending. When thinking of caffeine, coffee is the first thing that comes to mind, but it’s important to remember that it’s also found in many other carbonated beverages. A recent study has come to confirm something you probably already suspected.
The study. A recent paper published in Nature by researchers from the University of Basel in Switzerland and the Institute of Neuroscience and Medicine at the Forschungszentrum Jülich in Germany revealed that consuming caffeine during a period of sleep restriction can worsen the negative effects on the brain’s gray matter.
In short, the researchers found that individuals who consumed caffeine while experiencing sleep deprivation showed more pronounced reductions in gray matter volume compared to those who didn’t consume caffeine.
Big mystery solved. Scientists embarked on a quest to address a long-standing question about caffeine. Caffeine is the most consumed psychoactive substance and is known for its ability to enhance alertness and mitigate cognitive deficits associated with sleep deprivation. However, there’s been uncertainty surrounding the relationship between caffeine consumption and sleep loss.
To be precise, the study aimed to investigate the impact of caffeine consumption on reductions in grey matter volume, which is crucial for information processing and cognitive function regulation. The research team studied the connection between chronic sleep restriction and daily caffeine intake, and thus focused on whether caffeine consumption during periods of sleep deprivation would exacerbate reductions in gray matter volume
Adenosine and caffeine. Adenosine is a neurotransmitter that promotes sleep and relaxation by binding to its receptors in the brain, reducing neuronal activity. When consumed, caffeine acts as a competitive antagonist of these adenosine receptors, blocking their effect. At the same time, this causes a decrease in sleepiness and an increase in alertness and energy. This interaction explains why caffeine is so effective in reducing fatigue and improving short-term cognitive and physical performance.
Based on this, the study aimed to investigate the role of the adenosine system, particularly the availability of adenosine A1 receptors, in mediating the brain’s response to caffeine and sleep deprivation.
Building on a previous study. In a previous study, researchers found that consuming caffeine led to a decrease in gray matter volume over 10 days, “which was independent of the caffeine-induced vasoconstriction and was only partially mitigated after 36 hours.” These findings formed the basis for the new study.
Nine days of consuming caffeine. The most recent study was carried out with 36 healthy adult participants (15 women and 21 men, around 29 years old) at the German Aerospace Center research facility in Cologne. The research team chose the participants based on their low daily caffeine intake (less than 450 mg) and non-smoking status.
The participants were split into two groups: one received coffee with caffeine (the “CAFF group”), and the other received decaffeinated coffee (the “DECAF group”). The study lasted nine days, starting with an adaptation day followed by two baseline days with 8 hours of sleep per night.
After this, the participants experienced five days of restricted sleep, with only 5 hours of sleep per night, and finished with a recovery day of 8 hours of sleep. During the sleep restriction phase, the CAFF group received 200 mg of caffeine in the morning and 100 mg in the afternoon, while the DECAF group received equivalent volumes of decaffeinated coffee.
MRI and PET. To measure the effects on gray matter volume, the volunteers underwent magnetic resonance imaging (MRI) and positron emission tomography (PET) scans in three phases: after the initial days, after the chronic sleep restriction phase, and after the recovery day. The team collected saliva samples from them regularly to monitor caffeine levels, ensuring accurate tracking of caffeine intake and its physiological effects.
Results. The study found that the presence of caffeine had a significant effect on gray matter volume during chronic sleep restriction, impacting the DECAF group as well. It showed that individuals with lower caffeine levels during sleep restriction displayed increased gray matter in multiple brain areas, including the prefrontal cortex, temporal-occipital cortex, and thalamus. Experts believe these regions have a compensatory mechanism to aid with sleep loss.
Increase in gray matter. The study found that participants in the DECAF group had different gray matter after long periods of sleep restriction, which came as a surprise. In fact, the paper suggests that a 2018 study proposed a different explanation for this.
To be exact, the researchers said, “This study examined the changes in gray matter along the course between 20 and 36 hours of wakefulness, and they found that multiple brain regions in fact started from showing an increase in the early stage (20 h) and turned to be a reduction later (36 h).”
Decrease in gray matter. On the other hand, participants in the CAFF group, who consumed caffeine during the sleep restriction phase, showed a decrease in gray matter volume in the same regions. The study suggests that caffeine may inhibit the brain’s compensatory mechanisms during periods of insufficient sleep, worsening the negative impact of sleep deprivation on brain structure.
Adenosine and its relationship with gray matter. Lastly, researchers discovered that individuals who consumed caffeine during periods of reduced sleep and “a lower availability of subcortical [adenosine receptors]” showed more significant reductions in gray matter. In other words, adenosine receptor activity seems to play a crucial role in influencing the impact of sleep deprivation and caffeine on brain structure.
Bottom line. The researchers in the paper suggest that caffeine consumption can mitigate sleepiness by interfering “with the brain plasticity induced by sleep loss.” However, it’s also important to note that caffeine doesn’t directly counteract or normalize gray matter changes, and the potential impact on cognitive and behavioral functions remains unclear.
This article was written by Miguel Jorge and originally published in Spanish on Xataka.
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