Dec 8, 2006
Everybody knows a few strong cups of coffee can turn some otherwise pleasant people into crabby bundles of anxiety, whose jitters give way to lethargy in the span of a few hours.
In others, the opposite is true -- a cup of coffee seems to chase away the grumpiness of the morning.
Less well known, even by scientists, are caffeine's mental effects in the longer term as a possible cause of psychological disorders.
As Starbucks expanded into its 38th country (Brazil) on Wednesday, new research from a Virginia scientist shows prolonged use of caffeine -- the world's most popular drug, used daily by four out of five people globally -- might literally drive you insane.
Five cups of brewed coffee per day, or the equivalent caffeine intake in tea or cola, made people more than twice as likely to exhibit adult antisocial personality disorder, and abuse of alcohol, cannabis or cocaine, according to Kenneth Kendler, director of the Virginia Institute for Psychiatric and Behavioural Genetics.
These heavy caffeine users were also almost twice as likely to exhibit panic disorder, generalized anxiety disorder and major depression.
Even among moderate users, the odds of exhibiting one of these illnesses were increased across the board, according to Kendler's survey of more than 3,600 adult twins, which appears in the December issue of Psychological Medicine.
These twins, who share all their genes as well as family history, but often differed in caffeine use, allowed his team to tease out the specific effects of the drug from the effects of the environment. He was not surprised by what he found, which he described as significant, but not profound -- and certainly no reason to give up one's morning hit or mid-afternoon pick-me-up.
"Any form of drug use is broadly related to aspects of psychopathology," he said in an interview. "You're consuming a substance that influences the way you think."
What does surprise him is that he was the first to find this link, however weak.
"It's very hard to get funding, because no agency is interested and Starbucks won't fund you, so we don't know a lot."