Good news for anyone who switched to decaf and worried they were missing out: a new study suggests some of coffee’s mood benefits may not depend on caffeine at all. Instead, they may come from what coffee does to the trillions of bacteria living in your gut.
The research comes from APC Microbiome Ireland at University College Cork and was published in the journal Nature Communications, according to ScienceDaily, which reported on it this week.
How the Study Worked
The researchers recruited 62 adults: 31 regular coffee drinkers who had three to five cups a day, and 31 people who didn’t drink coffee.
The coffee drinkers first gave up coffee entirely for two weeks. Then they were given either regular or decaffeinated coffee. Throughout, the team tracked their mood, their thinking skills and the makeup of their gut bacteria.
What They Found
Both regular and decaf coffee were linked to lower scores for stress, depression and impulsivity. That’s the headline finding, and it’s why decaf drinkers can take heart.
Coffee in either form was also tied to higher levels of certain gut bacteria, including species called Eggerthella and Cryptobacterium curtum. Coffee drinkers also showed more of a group of bacteria called Firmicutes, which the researchers linked to positive emotions in women.
The two kinds of coffee did seem to help in different ways:
- Decaf was associated with better learning and memory.
- Regular coffee was associated with less anxiety, better attention and alertness, and a lower risk of inflammation.
Why Your Gut Talks to Your Brain
Scientists call the connection the “microbiota-gut-brain axis.” It’s the idea that the bacteria in your digestive system influence your brain through several pathways, including the immune system, hormones, nerves and the chemicals those microbes produce.
Because decaf showed benefits too, something in coffee other than caffeine may be at work. This study adds evidence that changes in gut bacteria could be part of how coffee affects how we feel.
The Fine Print
Before you brew a third pot, keep this in perspective. This was a small study, and the researchers are careful about what it can and can’t prove.
“Because the study involved a relatively small number of participants, the findings do not establish that coffee directly causes these changes in mood, cognition, or gut health,” said Professor John Cryan, one of the researchers, according to ScienceDaily.
In other words, it’s a promising lead, not a prescription. Coffee isn’t a treatment for depression or anxiety, and anyone struggling with those should talk with a doctor.
How Much Is Too Much?
If you enjoy coffee, the federal government offers a useful guide. The Food and Drug Administration says that for most healthy adults, 400 milligrams of caffeine a day, “about two to three 12-fluid-ounce cups of coffee,” is an amount not generally associated with negative effects.
Notice that the coffee drinkers in this study were having three to five cups a day, and cup sizes vary. If you’re near the top of that range with large mugs, you may be over the FDA’s benchmark.
Decaf is a good option if you want the flavor, and possibly some of these gut benefits, without the jitters. The FDA says decaf typically has 2 to 15 milligrams of caffeine in an 8-ounce cup, a small fraction of regular coffee.
The FDA also advises checking with your health care provider about caffeine if you are pregnant, trying to become pregnant or breastfeeding, or if you have certain medical conditions or take medications that make you more sensitive to caffeine. Too much caffeine can cause a racing heart, anxiety, trouble sleeping and digestive problems, the agency notes.
Practical Tips for the Coffee Drinker
- Enjoy it black or close to it. The study looked at coffee itself, not sugary coffee-shop drinks loaded with syrups and whipped cream.
- Consider a half-caf afternoon. Swapping your later cups for decaf can keep the ritual and the flavor while cutting caffeine before bed.
- Keep your own records. If you want to know how coffee affects you, jot down how you feel and how you sleep for a couple of weeks. You’re the best judge of what works for your body.
The Bottom Line
For millions of Americans, the morning cup is a small, dependable pleasure. This study hints that it may be doing a little more good than we thought, and that even decaf drinkers may share in it. Enjoy it in moderation, go easy on the sugary add-ons, and keep an eye out for bigger studies that can confirm what these researchers found.