Journal Title (Medline/Pubmed accepted abbreviation): Am J Clin Nutr
Page numbers: 509-514
Summary of Background and Research Design
Background:It is somewhat controversial whether or not caffeine consumption is associated with an increased risk of developing atrial fibrillation (AF). Although many patients with AF indicate coffee as a trigger for arrhythmia, and although there is a widespread belief that caffeine intake is related to the development of AF, there is little information to support this assumption. Recent studies have actually failed to confirm prior concerns that coffee consumption may increase the risk of coronary artery disease or stroke and suggest that it does not confer greater risk of hypertension, and may even protect from type 2 diabetes.
Hypothesis/purpose of study: The relation between caffeine intake and incident AF was prospectively assessed.
Subjects:33,638 initially healthy women who participated in the Women's Health Study and who were > 45 years of age and free of cardiovascular disease and AF at baseline
Experimental design: Prospective observational study (non-experimental)
Treatments and protocol: Subjects were prospectively followed for incident AF from 1993 to March 2009. All women provided information on caffeine intake via a 131-item food-frequency questionnaire (FFQ) at baseline and in 2004 when randomization ended. Intake of specific amounts of foods including coffee, decaffeinated coffee, tea, caffeinated and decaffeinated cola, and chocolate was assessed on a scale of 9 responses ranging from Never to >= 6 times/day. Caffeine consumption was calculated based on the US Department of Agriculture (USDA) food composition data and supplementary data provided by food manufacturers. Women who reported an incident AF event on >=1 yearly questionnaire were sent an additional questionnaire to confirm the episode and collect additional information. These women were also asked for permission to review their medical records. An incident AF event was confirmed if there was electrocardiographic (ECG) evidence of AF or if a medical report clearly indicated a personal history of AF.
Summary of research findings:
- Median caffeine intakes across increasing quintiles of caffeine intake were 22, 135, 285, 402, and 656 mg/d, respectively
- During a median follow-up of 14.4 years (interquartile range: 13.8 to 14.8 yr), 945 AF events occurred
- Age-adjusted incidence rates of AF across increasing quintiles of caffeine intake were 2.15, 1.89, 2.01, 2.24, and 2.04 events, respectively, per 1,000 person-years of follow-up
- Using the first quintile as the referent, the multivariate-adjusted hazard ratios (95% confidence intervals) for increasing quintiles of caffeine intake were: 0.88 (0.72-1.06); 0.78 (0.64-0.95); 0.96 (0.79-1.16); and 0.89 (0.073-1.09). The P value for linear trend was non-significant (P = 0.45). Thus, no significant relationship was shown between caffeine intake and AF in this cohort.
- None of the individual components of caffeine intake (coffee, tea, cola, or chocolate) were significantly associated with incident AF
- Women with elevated caffeine consumption smoked more often and consumed more alcohol but had lower prevalence of hypertension and type 2 diabetes
Interpretation of findings/Key practice applications:
In this large cohort of initially healthy, middle-aged women, elevated caffeine consumption was not associated with an increased risk of incident AF. These results are consistent with findings from the prospective Danish Diet, Cancer, and Health Study and additional experimental studies. Strengths of this study include prospective design, sample size, long-term follow-up with large number of confirmed events, and the possibility of updating caffeine consumption during follow-up. Limitations of the study include the inability to evaluate short-term effects of caffeine on AF in this study, heterogeneity of the study population that may limit extrapolation to male and non-white subjects, and the difficulty adequately defining an initial episode of AF. It is also not clear whether these findings could be generalized to men. Despite these limitations, the data presented in this study suggest that elevated caffeine consumption does not contribute to the increasing burden of AF in the population.