One group of Americans drinks more caffeinated beverages than all others.
That's people who smoke cigarettes and also have serious mental illness, including schizophrenia and bipolar disorder, according to new research.
While Americans overall are drinking more caffeinated beverages than ever, this group consumes the highest amount and also has the highest risk of negative health consequences, said researcher Dr. Jill Williams, director of addiction psychiatry at Rutgers Robert Wood Johnson Medical School in New Jersey, and colleagues.
“Caffeine is generally considered safe and even has some health benefits,” Williams said in a Rutgers news release. “But we just don't understand the cognitive and psychiatric effects of high caffeine intake, especially among smokers with mental illness.”
The researchers analyzed data from 248 adult smokers who were recruited during a previous study.
Participants were either outpatients with schizophrenia or bipolar disorder or from a control group with no psychiatric diagnoses. Each smoked a pack a day.
Researchers collected blood samples from the participants to measure their serum caffeine levels. Participants also completed surveys on smoking history, caffeine use, physical health and psychological symptoms.
While caffeine intake was highest in those with bipolar disorder, followed by schizophrenia, it was lowest in the control group.
Williams suggested several theories that might help explain why this connection exists. First, there's a well-established association between caffeine and smoking. People who have mental illnesses tend to smoke at rates two to three times higher than the general population.
The tars in cigarette smoke increase the metabolism of caffeine, so to get the stimulating effects, a smoker needs more of it, she said.
It's also possible that caffeine works as a type of self-medication through adenosine receptors in the body, Williams theorized.
Mood, especially bad mood, is also linked to caffeine take.
People with mental illnesses also seem to be more vulnerable to addictive substances.
Williams suggested that each of these ideas could be further investigated.
Caffeine is a widely used psychoactive drug, the study noted. It's known for increasing alertness and attention. It can also lead to anxiety, insomnia, excess stomach acid and heartburn at too-high doses.
Most healthy adults can safely consume up to 400 milligrams a day, about 4 cups of brewed coffee. The researchers note that consuming more than 600 milligrams isn't advised and can lead to anxiety, insomnia, excess stomach acid and heartburn.
“Today, people consume huge amounts of caffeine in more concentrated forms -- like energy drinks or double shots of espresso -- far more than when our participants were surveyed,” Williams said. “And yet, the effects of high caffeine intake remain widely understudied. This is particularly true for people with mental illness.”
The findings were recently published in Psychiatry Research.
The U.S. Food and Drug Administration has more on caffeine.
SOURCE: Rutgers University-New Brunswick, news release, Feb. 28, 2023