Drinking a cup of coffee a day could alter the volume of gray matter in your brain, according to a new study in the journal Cerebral Cortex. Surprisingly, however, the study authors also found that caffeine consumption appears to have no effect on sleep quality, contradicting a commonly held belief about the popular psychostimulant.
Gray matter generally comprises the brain’s outermost layer and consists of neuronal cell bodies, otherwise known as soma. White matter, meanwhile, is made up of the connecting branches that link neurons together, along which electrical signals are transmitted.
The idea of your morning Americano or cappuccino altering the structure of your gray matter might sound pretty alarming, but the researchers are keen to point out that these changes appear to be temporary, and that just ten days of abstinence from caffeine is enough to reverse this effect.
“Our results do not necessarily mean that caffeine consumption has a negative impact on the brain,” explained study author Dr. Carolin Reichert in a statement. “But daily caffeine consumption evidently affects our cognitive hardware, which in itself should give rise to further studies.”
To conduct their experiment, the researchers recruited 20 healthy volunteers, all of whom were daily coffee drinkers. Over a ten-day period, participants were instructed to take three 150-milligram caffeine capsules a day, while abstaining from all other sources of caffeine. This protocol was then repeated for another ten days, during which participants were given placebo tablets.
At the end of each ten-day block, the study authors scanned participants’ brains using functional magnetic resonance imaging (fMRI), while also measuring their brain activity as they slept. Results indicated that gray matter volumes decreased after regular caffeine use, but increased after ten days of abstinence from the drug.
These effects were particularly noticeable in the right medial temporal lobe, which contains key structures such as the hippocampus, parahippocampus, and fusiform gyrus, and is associated with memory function. To analyze the impact of these changes, the researchers asked participants to complete a series of working memory tasks and found that they generally performed better after abstaining from caffeine for ten days than they did after consuming caffeine.
Somewhat surprisingly, the researchers also noted that slow-wave activity (SWA) during sleep was completely unaffected by either caffeine consumption or changes in gray matter volume. This came as something of a surprise, given that many people report disrupted sleep after ingesting caffeine.
Because of this, the study authors had expected to find a correlation between altered gray matter and SWA following regular caffeine consumption. According to their paper, caffeine is known to increase neuronal activity during waking hours, thereby raising the energetic demands placed on neurons. During sleep, SWA allows for these neurons to recovery from their daily exertions, all of which has led scientists to assume that caffeine consumption and SWA must be linked in some way.
However, after analyzing their findings, the study authors concluded that “the data do not suggest a link between sleep depth during daily caffeine intake and changes in brain morphology.”
Summing up the significance of this research, Reichert explained that “the changes in brain morphology seem to be temporary, but systematic comparisons between coffee drinkers and those who usually consume little or no caffeine have so far been lacking."