A pilot study of plasma caffeine concentrations in a US sample of smoker and nonsmoker volunteers

Jose De Leon, Francisco J. Diaz, Thea Rogers, Debra Browne, Lori Dinsmore, Omar H. Ghosheh, Linda P. Dwoskin, Peter A. Crooks

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69 Scopus citations


Even though 85% of adults drink caffeinated beverages daily, very limited studies on plasma caffeine concentration in the US population have been published. Smoking induces cytochrome P450 1A2 (CYP1A2), which is the main enzyme involved in caffeine metabolism. The current naturalistic pilot study explores plasma caffeine concentrations in a US sample, and presents a mathematical model of the relationship between caffeine intake and plasma concentrations for smokers and nonsmokers. Caffeine intake and average plasma caffeine concentrations from morning (7:30-9:30 a.m.) and afternoon (2:00-4:00 p.m.) samples were studied in 69 volunteers (21 smokers and 48 nonsmokers). The mean caffeine intake obtained from caffeinated beverages was 3.02 mg/kg/day, which is similar to the intake in the US population. Almost all subjects in the present sample (99%; 95% confidence interval [CI]: 96-100) had detectable plasma caffeine concentrations. Smokers had significantly higher caffeine intake than nonsmokers. The ratio of concentration/dose of caffeine from caffeinated beverages was approximately four-fold higher in nonsmokers (1.33 kg×day/l) than in smokers (0.29 kg×day/l). According to the model, the median plasma caffeine concentration was two- to three-fold higher in nonsmokers for each level of caffeine intake. Our model improves our understanding of the interactions between caffeine and smoking. Additional studies are needed to replicate the model. This model may help epidemiologists to correct for the effects of smoking on caffeine intake and pharmacologists to screen for the activity of CYP1A2.

Original languageEnglish
Pages (from-to)165-171
Number of pages7
JournalProgress in Neuro-Psychopharmacology and Biological Psychiatry
Issue number1
StatePublished - Feb 2003

Bibliographical note

Funding Information:
This study was partly supported by grants MH-51380 from the National Institute of Mental Health (JdL); DA-08656 (LD and PC) and DA-00399 (LD) from the National Institute of Drug Abuse; a National Alliance for Research in Schizophrenia and Depression (NARSAD) Young Investigator Award (TR) and a supplement to the NARSAD grant from Department of Mental Health and Mental Retardation/Department of Psychiatry University of Kentucky through University Collaboration Project (TR). FD was supported by a grant from the Kentucky Department of Mental Health and Mental Retardation and the Department of Psychiatry of the University of Kentucky through the University Collaboration Project, and by a fellowship from the Department of Statistics of the University of Kentucky. OG was a graduate student in the Pharmaceutical Sciences PhD program at UK during the course of this study. Jenny Boyle, BS, Jimmie Brumagen, RN, Lynn Weddle, RN and Meg Susce, RN helped with the data collection.


  • Caffeine
  • Cytochrome P450 1A2
  • Metabolism
  • Smoking
  • Tobacco

ASJC Scopus subject areas

  • Pharmacology
  • Biological Psychiatry


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