Does caffeine really cause poor sleep?

We’ve all heard the infamous warning (especially as children), “Don’t drink any coffee, tea or soda before you go to bed — you won’t be able to sleep.” Of course, this was typically followed by the requisite “if you have a poor night’s sleep you won’t be able to function properly the next day…” But can regular caffeine consumption affect brain structure due to poor sleep? A research team led by Dr Carolin Reichert and Professor Christian Cajochen of the University of Basel and UPK (the Psychiatric Hospital of the University of Basel) set out to answer this question in a new study.

The study, Daily Caffeine Intake Induces Concentration-Dependent Medial Temporal Plasticity in Humans: A Multimodal Double-Blind Randomized Controlled Trial included “20 healthy young individuals” (a bit random as neither the gender nor actual ages were stated) who all drink coffee daily. They were given tablets to take over two 10-day periods and were asked not to consume any other caffeine during this time. During one test period, they received tablets with caffeine; in the other, placebos (that is, tablets with no active ingredient). At the end of each 10-day period, the researchers examined the volume of the subjects’ gray matter by means of brain scans. They also investigated the participants’ sleep quality in the sleep laboratory by recording the electrical activity of the brain (EEG).

Surprisingly, the researchers found that the caffeine consumed as part of the study did not result in poor sleep. However, as reported in the journal Cerebral Cortex, (Volume 31, Issue 6, June 2021) they observed changes in the gray matter. Gray matter refers to the parts of the central nervous system consisting primarily of the cell bodies of nerve cells, while white matter mainly comprises the neural pathways, the long extensions of the nerve cells.

The data revealed that the participants’ depth of sleep was equal, regardless of whether they had taken the caffeine or the placebo capsules. But they saw a significant difference in the gray matter, depending on whether the subject had received caffeine or the placebo. After 10 days of placebo – abstaining from caffeine – the volume of gray matter was greater than following the same period of time with caffeine capsules.

Apparently, the difference was particularly evident in the right medial temporal lobe, including the hippocampus, a region of the brain that is essential to memory consolidation. “Our results do not necessarily mean that caffeine consumption has a negative impact on the brain,” Dr Reichert told “But daily caffeine consumption evidently affects our cognitive hardware, which in itself should give rise to further studies.”

However, the researchers found that although caffeine appears to reduce the volume of gray matter, after just 10 days without coffee it had significantly regenerated in the test subjects. Thus, the changes in brain morphology appear to be temporary, but, according to Reichert, “systematic comparisons between coffee drinkers and those who usually consume little, or no caffeine have so far been lacking.”

It should be noted that this study, as with so many coffee/caffeine studies, was another one based on “observational” analysis. Interestingly, Reichert pointed out that in the past, the health effects of caffeine have been investigated primarily in patients but suggested there is a need for research on healthy subjects. I find it strange that the health effects of caffeine have been studied predominantly in “patients” and not equally in “healthy caffeine drinkers,” I would also suggest a larger pool of test subjects with more age diversity and a longer test period.

For now, I will continue to consumer my multiple daily cups of coffee but maybe just not too late in the evening… But shall I have the roast from Colombia with notes of peach, honey and caramel or the roast from Brazil with notes of melon and nuts…

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