People who take in the caffeine equivalent of three cups of brewed coffee (or seven cups of instant) are more likely to hallucinate, a new study suggests.
The researchers found that people with a caffeine intake that high, whether it came from coffee, tea, chocolate or caffeinated energy drinks or pills, had a three-times-higher tendency to hear voices and see things that were not there than those who consumed the equivalent of a half-cup of brewed coffee (or one cup of instant coffee).
Though most people who drink loads of coffee are not known to hallucinate seriously, when these types of experiences interfere with daily functioning, they are considered to be psychotic.
Seven cups of instant coffee contain a total of 315 milligrams of caffeine, according to data used by the researchers. That translates to about six cups of strong tea, nine colas, four Red Bulls and about one-and-a-half cups of coffee at a boutique café.
Wide range of effects
Caffeine is a central nervous system stimulant that temporarily wards off drowsiness and restores alertness. Some 90 percent of North Americans consume some of form caffeine every day. It is the world's most widely used drug, researchers say.
Caffeine is completely absorbed by the stomach and small intestine within 45 minutes of ingestion.
In moderation, caffeine can increase the capacity for mental or physical labor, but when used in excess, it also can be intoxicating, causing nervousness, irritability, anxiety, muscle twitching, insomnia, headaches and heart palpitations, other studies have shown.
The researchers at Durham University say the findings will contribute to the beginnings of a better understanding of the effect of nutrition on hallucinations and other forms of psychotic behavior, such as delusions and schizophrenia. Changes in food and drink consumption, including caffeine intake, could help people cope with or prevent hallucinations, say the scientists. The results are detailed in the journal Personality and Individual Differences.
Caffeine exacerbates stress
In the study, funded by the Economic and Social Research Council and the Medical Research Council, 200 non-smoking students at a United Kingdom university were asked about their typical intake of caffeine-containing products, such as coffee, tea and energy drinks, as well as chocolate bars and caffeine tablets.
Their stress levels and their propensity to have hallucinatory experiences were also assessed. Seeing things that were not there, hearing voices, and sensing the presence of dead people were amongst the experiences reported by some of the participants.
The explanation could be that caffeine has been found to exacerbate the physiological effects of stress. When under stress, the body releases a stress hormone called cortisol. More of this hormone is released in response to stress when people have recently had caffeine.
This extra boost of cortisol may link caffeine intake with an increased tendency to hallucinate, said study leader Simon Jones, a graduate student at Durham's Psychology Department.
Jones and his colleague assumed that psychotic experiences, including hallucinations, "exist on a continuum stretching into the healthy population," so they studied the relationship between caffeine and hallucinations in a healthy population, rather than a population of mental patients or those on antipsychotic medication. Previous research has highlighted a number of factors, such as childhood trauma, which may lead to clinically relevant hallucinations, Jones said.
Many such factors are thought to be linked to hallucinations in part because of their impact on the body's reaction to stress. Given the link between food and mood, and particularly between caffeine and the body's response to stress, it seems sensible to examine what a nutritional perspective may add.
"Hallucinations are not necessarily a sign of mental illness," Jones said. "Most people will have had brief experiences of hearing voices when there is no one there, and around three percent of people regularly hear such voices. Many of these people cope well with this and live normal lives."
Those who cannot cope should seek professional help.
Caffeine for coping?
It is possible that the association between caffeine intake and hallucinations was due to the fact that people who are prone to associations tend to use caffeine to help them cope with their experiences, said Durham psychologist Charles Fernyhough, who worked with Jones on the research.
"More work is needed to establish whether caffeine consumption, and nutrition in general, has an impact on those kinds of hallucination that cause distress," Fernyhough said.
Research in this area continues and the public can take part in studies at www.dur.ac.uk/s.r.jones.