It’s been nearly 30 years since the scientific community first developed a serious interest in exploring the interactions between the bugs in our guts and the neurons in our brains. Researchers have since demonstrated how psychological states can trigger gastrointestinal disorders while also showing how dietary decisions — and their impact on the microbial mix in the gut — can affect neurological function.
So I guess it was only a matter of time before they would wake up and smell the coffee.
For as long as the magical bean has been brewed, people have been quaffing cups to jolt themselves out of a morning fog or a midafternoon slump. There’s clearly some interaction with the brain after the first few sips reach the digestive system. But the latest research, published last week in Nature Communications, looked more specifically at how the brew might affect the brain’s cognitive function via the gut microbiome. And — spoiler alert — it’s not about the caffeine.
A team of researchers from University College Cork recruited 62 study participants, half of whom were not coffee drinkers. The other half, who regularly drank three to five cups a day, were instructed to abstain for two weeks (gasp!), during which time they and the nondrinkers submitted to psychological assessments and contributed stool and urine samples to reveal the microbial mix in their guts. That break from the bean, researchers discovered, caused significant metabolite changes in the digestive systems of the coffee drinkers.
When those coffee lovers were allowed to resume their consumption, they were not privy to the caffeine content: Half of them were given caffeinated coffee, while the other half drank decaf. Updated stool and urine samples from the caffeinated group revealed a notable increase in Firmicutes CAG:94, a strain of bacteria known to promote positive emotions, perhaps explaining the upbeat results of their psychological assessments. Those drinking decaf, on the other hand, displayed improved scores on learning and memory tests (researchers suspect related factors, including improved sleep, may be the reason why).
“Our findings reveal the microbiome and neurological responses to coffee, as well as their potential long-term benefits for a healthier microbiome,” explains study coauthor John Cryan, PhD. “Coffee may modify what microbes do collectively, and what metabolites they use. As the public continues to think about dietary changes for the right digestive balance, coffee has the potential to also be harnessed as a further intervention as part of a healthy balanced diet.”
Before you consider upping your overall coffee intake, you might want to know that the study was funded by the Institute for Scientific Information on Coffee, a research organization owned and controlled by a global consortium of coffee producers. That funding source might give you pause, but the importance of the gut-brain connection is reinforced by a Stanford University study published last month in the journal Nature that has nothing whatsoever to do with your coffee habit.
“Although memory loss is common with age, it affects people differently and at different ages,” says lead study author Christopher Thaiss, PhD. “We wanted to understand why some very old people remain cognitively sharp while other people see significant declines beginning in their 50s or 60s. What we learned is that the timeline of memory decline is not hardwired; it’s actively modulated in the body, and the gastrointestinal tract is a critical regulator of this process.”
Thaiss and his team caged young and old mice together in close quarters, where they lived and — most importantly — pooped for a month. The bacterial mix in their waste, researchers reasoned, would make its way into the guts of the two groups of mice, allowing them to test its effects on their cognitive performance.
The mingling of microbes didn’t seem to lead to a significant change in the gut microbiomes of the old mice, but it made the bacterial mix in the young ones resemble that of the older cohort. And the young mice subsequently performed more poorly on cognitive tests than their peers, suggesting that the mix of microbes in the gut may play a role in neurological function.
Researchers pointed to the abundance of a specific type of bacteria — Parabacteroides goldsteinii — in old mice that seemed to be associated with cognitive decline. When they activated the vagus nerve in those mice, however, their performance on the tests equaled that of their younger counterparts.
“Basically, we’ve identified a three-step pathway toward cognitive decline that starts with gastrointestinal aging and the subsequent microbial and metabolic changes that occur,” Thaiss explains. “The myeloid cells in the GI tract sense these changes, and their inflammatory response impairs the connection between the gut and the brain via the vagus nerve. This is a direct driver of memory decline. And if we restore the activity of the vagus nerve, we can restore an old animal’s memory function to that of a young animal.”
Because vagus-nerve stimulation has been approved by the Food and Drug Administration, Thaiss believes that the findings may eventually inform clinical treatment for age-related cognitive dysfunction.
While you’re digesting that future possibility, go ahead and grab another cup of coffee. It can’t hurt.
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