A lot of conflicting data have emerged about the health effects of caffeine consumption that suggest it may actually be beneficial for health. For example, a very large study published in The New England Journal of Medicine in 2012 reported that regular coffee intake was associated with a lower risk of dying from a variety of diseases. Yet, long-standing dogma in medicine has maintained that this popular beverage (or other caffeine-containing drinks) has adverse cardiovascular effects as a result of its stimulant nature. In particular, quantitative assessment of caffeine intake is part of the diagnostic workup for new atrial fibrillation (AF) and reduction in caffeine consumption is a strong recommendation as part of AF patient education.
A recent meta-analysis, however, published in The Canadian Journal of Cardiology is challenging this long-standing risk designation. This study analyzed 6 prospective cohorts with a total study population of 228,465 participants. Surprisingly, regular caffeine intake was weakly associated with a 10% lower incidence of AF (95% CI, 0.81-1.01). Subgroup analysis of pooled results, which adjusted for confounders, achieved statistical significance, for both low doses (relative risk reduction 11%) and high doses (relative risk reduction 16%) of caffeine intake. In addition, the authors conducted a dose-response meta-analysis and concluded that the incidence of AF decreased by 6% for every 300 mg/d increment in caffeine intake.
The strength of this large prospective study is that it provides substantial evidence that caffeine intake does not increase or adversely affect incident AF. Whether caffeine intake is protective warrants additional investigation although the authors suggest that the mechanism underlying this protective effect may be via the anti-fibrotic properties of caffeine. Some limitations of the study include the observational nature of this data, which is susceptible to confounding, the small number of AF events, and the use of self-reporting to assess caffeine intake. Additional validation of these findings is needed by a randomized trial, with careful attention paid to comorbidities, such as sleep apnea.
Despite the dose-dependent relationship of caffeine and AF, there may be other cardiovascular toxicities of excess doses of caffeine and therefore patients should not be advised to increase caffeine intake to protect themselves from AF. However, based on these data, it is reasonable to not strictly limit caffeine intake in those with new-onset AF.
Cheng M, Zunsong H, Xiangfeng L, et al. Caffeine intake and atrial fibrillation incidence: dose-response meta-analysis of prospective cohort studies. Can J Cardiol. 2014; doi:10.1016/j.cjca.2013.12.026.