Adult smokers suffering from mental illnesses such as bipolar disorder and schizophrenia were found to consume high caffeine levels compared to the general population, a recent study reported . Importantly, these individuals are also at greater risk of adverse health effects.
The study, published in the Psychiatry Research journal, observed that this group also tops the chart of those most likely to experience negative health consequences.
Lead author of the study, Jill M. Williams, the director of the division of addiction psychiatry at the Rutgers Robert Wood Johnson Medical School, stated that caffeine is initially recognized as having some health benefits and being generally safe for consumption.
However, she noted that there is still little information on the relationship between very high caffeine intake and psychiatric symptoms and cognitive performance among smokers with mental illness.
Caffeine and the brain function
Caffeine ranks amongst the most actively and widely used psychoactive drugs in the UK and the United States. The main effects of caffeine include increased attention, alertness and vigilance.
A daily dose of up to 400 milligrams of caffeine is considered generally safe. This dose translates to about four cups of coffee per day. However, taking more than this dose or at least 600 mg of caffeine daily can lead to insomnia, heartburn, anxiety, and excess stomach acids.
Most studies on the effects of excessive caffeine on executive functioning have been done amongst healthy adults. The effects of excessive caffeine on higher functioning of the brain, which includes critical thinking and decision-making, in adults who smoke and have mental illness remain unknown.
Even among healthy adults, the effects of doses as high as 600 mg daily of caffeine intake were mixed. One review  showed that sleep-deprived individuals who took 600 mg of caffeine showed improvements in judging complex emotional expressions.
In contrast, the same review revealed that gamblers who did not sleep for 75 hours and who consumed caffeine totaling 800 mg per day did not demonstrate improvements in risk-taking.
The study suggested that, while caffeine promotes vigilance and alertness, its impact on complex emotional discernment, decision-making and judgment in sleep-deprived individuals remained uncertain.
However, lower doses of caffeine increased alertness in sleep-deprived individuals, with the effects as dose-dependent. Moderate amounts of 100-300 mg daily are suggested to be effective in improving cognitive performance, while higher doses or above 400 mg are more likely to impair performance and result in anxiety.
How caffeine influences cognitive function?
To explore how caffeine influences cognitive performance and impacts psychiatric symptoms in smokers with mental illness, Williams and colleagues recruited 248 current adult smokers. All were pack-a-day smokers.
The participants were grouped into adult smokers with no psychiatric diagnoses and those with bipolar disorder and schizophrenia. The mean age was 40.85 years old. Participants agreed to participate in the study.
At the beginning of the research study, all completed a questionnaire related to caffeine use, smoking history, psychological symptoms and physical health. The participants gave consent to have their blood samples taken in order to measure caffeine levels in their serum.
The study’s findings revealed that those with bipolar disorder consumed an average of 195.3 mg of caffeine in 24 hours. This was followed by adults with schizophrenia, who consumed an average of 155 mg of caffeine. The control group consumed 131.7 mg of caffeine in the same period.
Caffeine serum levels were likewise investigated in the study. Those with bipolar disorders had the highest caffeine serum level at an average of 1725 ng/ml. Those with schizophrenia had serum caffeine levels of 1194 ng/ml. The control group only had 613.2 ng/ml.
The results appear to show that adults with mental illness tend to consume high caffeine. Results indicated a subgroup of patients with severe mental health conditions has high caffeine intake.
Theories on the relationship between caffeine and mental illness
The lead author of the study, Williams, explained that there are several theories on why there is a relationship between mental illness and caffeine intake:
- The first theory is based on a link between smoking and caffeine intake. Individuals with serious mental illness smoke more than the general population at a rate of two or three times higher. The tars present in cigarette smoke have been shown to increase the breakdown or metabolism of caffeine. As a result, individuals need to take more caffeine to achieve its effects, such as increased cognitive performance and alertness.
- A second theory focuses on the self-medication effect of high caffeine intake in those with mental illness.
- A third theory suggests that people with mental health conditions seem more vulnerable to addictive substances, including caffeine. This places them at a higher risk of excessively taking caffeine. Increased intake of high amounts of caffeine can result in negative consequences. The researchers added that caffeine is associated with negative emotions and moods.
All the theories presented to explain the link between caffeine and mental illness still need to be verified in large clinical trials.
Caffeine: benefits and disadvantages
Caffeine is present in at least sixty plants across the world. It is known to be a natural pesticide, and is toxic to several animals and insects. Caffeine is a protecting agent and allows the plant to defend itself from predators.
Caffeine’s stimulatory effects have been well-known for centuries. It is the most commonly consumed psychostimulant all over the world.
Caffeine is predominantly ingested as coffee but is also present in food or beverages such as cocoa, chocolate, tea, energy drinks and soft drinks. All countries sell some variations of caffeinated beverages, making them part of the world’s diet.
When present in moderate amounts, caffeine has been associated with:
- Lowered risk of developing Alzheimer’s disease and other neurodegenerative diseases
- Reduced memory deficits and beta-amyloid production in animal models of Alzheimer’s disease.
- Prevention of the loss of dopaminergic neurons and motor symptoms in Parkinson’s disease, as shown in animal model studies.
However, excessive intake of caffeine or coffee can lead to the following:
- Tachycardia (rapid heart rate)
- Shaking and restlessness
- High blood pressure
- Muscle breakdown
Take home message
The recent study by Williams et al revealed that too much caffeine among smokers with mental illness could have adverse health consequences. Hence, those with mental illness who smoke may benefit from support to prevent them from taking excessive amounts of caffeine.
While there are several theories on why this subgroup tends to be more addicted to coffee or caffeine, helping them manage their caffeine intake could help promote better health for these individuals.
When consumed in moderate amounts, caffeine can lead to increased alertness and better cognitive performance. However, excessive amounts have been well-documented to cause symptoms ranging from restlessness to addiction and nervousness. All these symptoms could be prevented by moderating caffeine intake.
Finally, the study added evidence that individuals with schizophrenia who also smoke are not the only group that could suffer from the ill effects of too much consumption of caffeine. This group appeared to be overtaken by patients with smokers with bipolar disorders in terms of susceptibility to very high caffeine consumption.
Although both groups are at the highest risk of negative health effects and adverse outcomes, those with bipolar disorders appeared more at risk of these consequences than those with schizophrenia.