There's nothing like a hot cup of your favorite caffeinated beverage to get you going in the morning, but for habitual drinkers a decaffeinated one may work just as well.

It sounds outrageous, but that's what researchers from institutions across Slovenia and the Netherlands found in a recent study comparing the effects of coffee – with caffeine, and without – on the brain and body.

The world drinks more than two billion cups of coffee each day, and the impacts of caffeine are well-understood. But for people trying to cut down on their intake, maybe because of anxiety or sleep problems that the drug can exacerbate, decaf could be a better option than we even realized.

"Anticipation plays a significant role, where participants expecting caffeine often experience similar cognitive and performance improvements regardless of whether they consume caffeine or a placebo," the researchers write in a paper describing their study.

To get a more detailed picture of this phenomenon, the researchers enlisted 20 healthy university students who were habitual coffee drinkers, averaging one to three cups per day.

Just before the study, the participants slept at least seven hours, abstained from drinking coffee for 8-11 hours, and consumed no food for two hours prior.

On arrival to the lab, their baseline electroencephalogram (EEG) and cardiovascular measurements were taken at rest. Then participants completed a mental arithmetic test designed to capture cognitive abilities, and an auditory 'oddball' task testing reaction time.

Then, they were split into two groups: one decaf placebo group, who were given decaffeinated coffee, and one caffeine group, who were given the same decaf coffee with an added 6mg of caffeine powder per kilogram of body weight.

After drinking their coffees, the participants rested for half an hour, before repeating the cardiovascular, EEG measurements, and cognitive performance tests.

While the participants' physiological responses and cognitive functioning did change after ingesting coffee, there were almost no significant differences in these changes between the decaf and caffeine groups.

Both groups experienced no significant improvement on their mental arithmetic tests post-coffee. But a cuppa joe, regardless of its caffeine content, significantly shortened participants' reaction times in the auditory test. Though the improvement was only statistically significant for the caffeine group, the findings suggest the placebo may also have a powerful effect.

"To our best knowledge, this has not been reported before. This could be due to an anticipation effect that comes from the habituation to coffee. In fact, habitual coffee drinkers have been shown to exhibit a reduction in reaction times when presented with the smell of coffee," the authors note.

Specific brain waves associated with cognitive processing increased when the oddball task was undertaken after coffee consumption, the EEG data revealed, though this was statistically significant only for the caffeine group.

Both groups experienced significant increases in blood pressure and decreased heart rates, which is the usual response for habituated coffee drinkers. The researchers were not expecting the cardiovascular effects to be so similar between drug and placebo.

All of this suggests caffeine is not the only power at work when it comes to surviving the morning grind: our expectations of this morning ritual contribute, too.

"Stimuli that closely mimic coffee can produce cognitive and physiological responses markedly similar to those of real coffee," the authors conclude.

"These findings suggest that regular coffee consumers respond to coffee-like beverages independently of the presence of caffeine."

This research was published in Heliyon.