Caffeine use is higher in smokers and in adults with serious mental illness. How does this impact patients with bipolar disorder and schizophrenia?
“Ms Pine” is a 52-year-old Caucasian woman with bipolar I disorder. Her most recent episode involved depression with psychotic features. Her mood disorder has been stable on ziprasidone, and she has had no psychiatric hospitalizations in the past 5 years.
She has smoked 2 or more packs of cigarettes per day for the past 30 years. Ms Pine also drinks a significant amount of caffeine every day. She regularly brings a 44-ounce cup of soda to clinic visits and says she drinks at least 2 of these cups every day. She also has comorbid hypertension and chronic obstructive pulmonary disease, for which she is adherent with medication.
At a recent outpatient appointment, Ms Pine noted that her mood was euthymic, with no evidence of psychosis. She reported sleeping 6 to 7 hours per night and denied experiencing significant anxiety. Ms Pine’s psychiatrist regularly provides her with psychoeducation on how to reduce her caffeine intake.
Almost 90% of adults in the United States use caffeine daily, consuming an average of 186 mg per day.1 Caffeine use is higher in smokers2 and in adults with serious mental illness.3 Caffeine improves cognition through increased alertness, attention, and vigilance via inhibition of adenosine receptors. Potential explanations for increased caffeine intake in patients with serious mental illness are listed in the Table.4,5
Despite the potential beneficial effects of caffeine, it may be harmful at higher doses.
The Current Study
Rosen and colleagues6 investigated rates of caffeine intake and blood caffeine levels in adult smokers with schizophrenia, adult smokers with bipolar disorder, and controls. The authors performed a secondary analysis of a larger study of nicotine intake and smoking behavior.7
Participants were 18 years and older who smoked 10 or more cigarettes per day and had a baseline expired carbon monoxide level greater than 8 ppm. Participants receiving nicotine replacement, clonidine, bupropion, or nortriptyline were excluded. Pregnancy, alcohol or other substance use disorder, and use of noncigarette tobacco products were also exclusionary.
At baseline, participants had a blood sample for caffeine and nicotine and its metabolites. They provided information about their smoking history and completed the Caffeine Consumption Questionnaire. Symptoms were assessed with the Positive and Negative Syndrome Scale and the Montgomery-Åsberg Depression Rating Scale. Multivariate gamma regression with a log link were used to identify predictors of blood caffeine levels and dietary caffeine intake.
The authors analyzed data on 80 participants with schizophrenia, 80 participants with bipolar disorder, and 88 controls. The mean participant age was 41 years, 58% were male, and 56% were Caucasian. Participants smoked an average of 21 cigarettes per day. Participants with bipolar disorder had the highest self-reported median daily caffeine intake (195 mg/day), followed by participants with schizophrenia (155 mg) and controls (132 mg).
A significant between-group difference for median blood caffeine levels was seen in participants with bipolar disorder (1725 ng/mL) and schizophrenia (1194 mg/mL) compared with controls (613 ng/mL).
In all 3 groups, 18% to 25% of participants consumed high daily doses (> 400 mg) of caffeine per day. There was a small but significant correlation between self-reported caffeine intake and blood caffeine levels (r = 0.17). In regression analyses, age, race (Black), and diagnosis (schizophrenia or bipolar disorder) were significant predictors of blood caffeine levels. Age and diagnosis (bipolar disorder) were significant predictors of self-reported caffeine intake.
Smokers with schizophrenia or bipolar disorder have higher blood caffeine levels than controls with similar smoking habits, the authors concluded. The primary sources of caffeine in participants were coffee and soda. Based on findings in the bipolar disorder group, increased caffeine was not solely attributable to effects of antipsychotic medications.
Study strengths included standardized timing of assessments and blood draws and the inclusion of controls who smoked the same amount as the patient groups. Potential limitations included potential confounding by metabolic or genetic factors and an inability to investigate effects of sleep and oral contraceptives on caffeine levels.
The Bottom Line
Caffeine intake is high in some patients with serious mental illness. An increased understanding of the effects of caffeine on cognition, psychopathology, and overall health is needed.
Dr Miller is a professor in the Department of Psychiatry and Health Behavior at Augusta University in Augusta, Georgia. He is on the editorial board and serves as the schizophrenia section chief for Psychiatric Times™. The author reports that he receives research support from Augusta University, the National Institute of Mental Health, and the Stanley Medical Research Institute.
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2. Swanson JA, Lee JW, Hopp JW. Caffeine and nicotine: a review of their joint use and possible interactive effects in tobacco withdrawal. Addict Behav. 1994;19(3):229-256.
3. Gandhi KK, Williams JM, Menza M, et al. Higher serum caffeine in smokers with schizophrenia compared to smoking controls. Drug Alcohol Depend. 2010;110(1-2):151-155.
4. Treloar HR, Piasecki TM, McCarthy DE, Baker TB. Relations among caffeine consumption, smoking, smoking urge, and subjective smoking reinforcement in daily life. J Caffeine Res. 2014;4(3):93-99.
5. Lara DR, Dall’Igna OP, Ghisolfi ES, Brunstein MG. Involvement of adenosine in the neurobiology of schizophrenia and its therapeutic implications. Prog Neuropsychopharmacol Biol Psychiatry. 2006;30(4):617-629.
6. Rosen RL, Ramasubramani RS, Benowitz NL, et al. Caffeine levels and dietary intake in smokers with schizophrenia and bipolar disorder. Psychiatry Res. 2023;319:114989.
7. Williams JM, Gandhi KK, Lu SE, et al. Nicotine intake and smoking topography in smokers with bipolar disorder. Bipolar Disord. 2012;14(6):618-627.