Participants who typically consumed caffeinated beverages also seemed to develop a tolerance to its anxiety-producing effects. Among regular caffeine drinkers, there was little difference in feelings of anxiety whether they'd been given a placebo or the real thing, while light caffeine drinkers reported significantly more anxiety after being given caffeine.
Dr. Peter Martin, a professor of psychiatry and pharmacology at Vanderbilt University, said the study is an interesting look at the biological effects of caffeine. However, not everyone who drinks lots of caffeinated beverages experiences withdrawal such as headaches when they cut back or quit.
And compared to other "drugs," the effects of caffeine are mild, and coffee and tea in particular may have other health benefits.
"That is the difference between statistical significance and clinical relevance," Martin said. "No one is going to change what they do, and there's no reason to change. There is a lot of data to suggest caffeine improves motor performance and memory performance."
A study released online May 12 in The Cochrane Library found caffeine helped prevent errors among shift workers and those who work at night.
The U.S. National Library of Medicine has more on caffeine.
SOURCES: Peter Rogers, Ph.D., professor, department of experimental psychology, University of Bristol, England; Peter Martin, M.D., professor, psychiatry and pharmacology, Vanderbilt University, Nashville, Tenn.; June 2, 2010, Neuropsychopharmacology, online
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