Adult smokers with mental illness consume most caffeine in U.S.: study

LOS ANGELES, Feb. 28 (Xinhua) -- A new study by researchers at Rutgers University found that adult smokers with mental illness consume the most caffeine in the United States.

The study, published recently in the journal Psychiatry Research, found that not only do adult smokers with bipolar disorder and schizophrenia drink the most caffeine, they are at the highest risk of negative health consequences.

Caffeine is one of the most widely used psychoactive drugs in the United States, with the main effects increased alertness, attention and vigilance.

While it is considered safe for most healthy adults to consume up to 400 milligrams of caffeine per day, consuming more than 600 milligrams can lead to anxiety, insomnia, excess stomach acid and heartburn, according to the study.

Researchers from Rutgers University and the University of California San Francisco analyzed data from 248 adult smokers. Participants were either outpatient smokers with schizophrenia or bipolar disorder or from a control group with no psychiatric diagnoses.

They found caffeine intake was highest among participants with bipolar disorder, followed by adults with schizophrenia.

There are several theories to explain the relationship between caffeine intake and mental illness, according to Jill M. Williams, director of the division of addiction psychiatry at Rutgers Robert Wood Johnson Medical School. One is that people with mental illnesses smoke at rates two to three times higher than the general population, and because the tars in cigarette smoke increase the metabolism of caffeine, it takes more caffeine to achieve stimulating effects.

Another theory links high caffeine intake to adenosine receptors and supports a possible self-medication effect among people with mental illness, according to Williams.