Frequent coffee drinkers develop a tolerance to its anxiety-producing effects and its effects as a stimulant, a new study suggests.
The research that took more than a year and involved roughly 400 subjects, some coffee drinkers and some not, was published Wednesday in the journal Neuropsychopharmacology.
The findings indicate that caffeine can bring frequent coffee-drinkers who have abstained for 16 hours back to their baseline level of alertness, but they won’t go above it.
“All that caffeine is doing to frequent caffeine consumers is keeping the normal level of alertness,” Peter Rogers, a professor of biological psychology at the University of Bristol in the U.K., said in a telephone interview.
“Because when you take caffeine away from them their alertness falls, they go into caffeine withdrawal ... you feel fatigued, headachy and so on and you need more caffeine just to get you back to the normal level.”
He said it’s possible that caffeine has other effects in terms of benefiting endurance or physical efforts, but these were not looked at in this particular study.
These study subjects were given either caffeine or a placebo during a full day of testing, Rogers said. They had to do a variety of tasks which included rating how alert they were, and able to concentrate, as well as how anxious they felt.
The medium- and high-caffeine consumers who got a placebo reported decreased alertness and increased headaches. Caffeine did not increase alertness in the participants who weren’t habitual coffee drinkers.
The outcomes also bolster previous research that found there is a genetic sensitivity to the anxiety-inducing effects of caffeine, Rogers said.
“What we added to that really was that we originally thought that that susceptibility might cause people to avoid caffeine,” he said.
But that wasn’t the case. In fact, people susceptible to those effects tended to drink more coffee than people who weren’t, he said, and it might be that they’re feeling a mildly pleasant buzz from the experience.
He suggested that one message for caffeine consumers is to stick with it, not to break away on weekends, for instance.
“If you’re a regular consumer during the week, if you have a different habit at the weekend that leads you to avoid it, then you will likely by Sunday to be feeling not so good, because you’d be deeper into caffeine withdrawal by then,” he said.