Cardiovascular effects of caffeinated beverages
Introduction
Tea and coffee are consumed on a daily basis by more than half of the American population. Attention to modifiable lifestyle-related factors is an important approach to the management of cardiovascular disease. Generally there is a public perception that the physicians approach is to prohibit perceived pleasures in life such as alcohol, tobacco and “junk food” however the situation may be different for caffeine. Due to their ‘stimulant’ properties, some patients and physicians alike are cautious regarding the intake of caffeinated beverages particularly in the presence of cardiovascular disease. However the 2015–20 Dietary Guidelines for Americans report a reduction in the risk of type 2 diabetes and cardiovascular disease with the consumption of 3–5 cups of coffee per day. We provide a concise, patient-centered review of key studies to determine the interaction between various caffeinated beverages and a broad spectrum of cardiac conditions. We hope this review will help guide clinicians in appropriately counselling patients with a range of cardiovascular conditions regarding caffeine intake, in particular tea, coffee and energy drinks.
Section snippets
Methods
We performed a comprehensive literature search in July 2018 of EMBASE, Web of Science, Medline and PubMed focusing on human and animal studies published in English examining effects of caffeine on cardiovascular disease. Key search terms were ‘caffeine, ‘coffee, ‘tea’, ‘energy drinks’ in combination with ‘diabetes’, ‘coronary artery disease’, ‘mortality’, ‘heart failure’, ‘arrhythmias’, ‘atrial fibrillation’, ‘sudden death’, ‘ectopy’ and ‘ventricular arrhythmias’. The highest quality studies
Pharmacology of caffeine
Caffeine, a methylxanthine alkaloid, is the key constituent in tea (1 cup ∼45 mg), coffee (1 cup ∼95 mg) and energy drinks (which often contain higher concentrations). Peak concentrations are reached 1 h following intake, with a half-life of ∼6 h. Table 1 summarizes the caffeine content of commonly consumed beverages. Caffeine interacts with different receptors in the cardiovascular system in a dose dependent manner. The physiological effects of caffeine on the cardiovascular system are
Hypertension
Regular consumption of tea or coffee has not been associated with long term effects on blood pressure. Acute rises in blood pressure have been reported early after coffee however are not sustained. In a meta-analysis of 5 randomized trials in hypertensive individuals, 200 –300 mg of caffeine acutely increased systolic BP by 8 mmHg (95% CI 5.7–10.6 mmHg) and diastolic BP by 5.7 mmHg (95% CI 4.1–7.4 mmHg) between 1 and 3 h post-ingestion. However tolerance develops quickly, and no difference in
Coronary artery disease
There are inconsistent and conflicting results regarding the impact of coffee consumption on coronary disease in part explained by evidence largely based on case control and cohort studies. Adenosine is a coronary vasodilator and its acute antagonism by caffeine impairs the expected increase in myocardial flow during exercise and has been shown in some studies to attenuate adenosine-induced hyperemia fractional flow reserve measurements during coronary angiography [19]. PET scan studies have
Cerebrovascular disease
Regular coffee consumption is associated with a significant reduction in stroke. In healthy individuals, a meta-analysis of 11 prospective studies reported coffee consumption of up to 6 cups/day was associated with a significant reduction in stroke risk (lowest with 3–4 drinks/day – RR 0.84; 95%CI 0.77–0.91) [25]. Both green and black tea were also found to be protective demonstrating a significant dose-related reduction in risk of ischemic stroke with moderate consumption of 3 cups/day (RR
Heart failure
Habitual coffee consumption is associated with reductions in incident hypertension and CAD, so it is not unexpected that observational studies indicate a lower incidence of heart failure (HF). In a meta-analysis of 5 prospective studies including 6522 heart failure events, a statistically-significant J-shaped relationship between coffee and HF was described, with the strongest benefit observed for 4 cups/day with an 11% lower risk [28]. An artistic rendering of potential benefits of moderate
Arrhythmias
While caffeine is commonly considered a trigger for arrhythmias by physicians and patients alike there is minimal evidence to support this misconception. Rather caffeine is associated with a mild reduction in the incidence of atrial fibrillation in observational studies. Electrophysiological and ambulatory monitoring studies in humans have failed to demonstrate proarrhythmia even at acute doses as high as 400 mg. Caffeine does not alter atrial or ventricular refractory periods, SVT or VT
Energy drinks and cardiovascular disease
There are increasing reports of adverse cardiovascular effects related to energy drinks (EDs). While a safe ‘acute’ dose of caffeine is considered to be 200–300 mg, some energy drinks contain up to 505 mg. Pro-arrhythmic effects are likely mediated by phosphodiesterase inhibition with increased intracellular calcium release and myofilament sensitivity. Heightened risk of AF, SVT, ventricular tachyarrhythmias, QTc interval prolongation and unmasking of Brugada syndrome have all been reported.
Mortality
Large scale prospective cohort studies suggest that tea and coffee consumption reduce cardiovascular and all-cause mortality. In the NIH–AARP Diet and Health Study spanning 5,148,760 person-years of follow-up with 52,515 deaths, coffee consumption was inversely associated with death (p < 0.001 for trend). Consumption as high as 4–5 cups/day was associated with the greatest benefit among both men (HR 0.88; 95%CI 0.84–0.93) and women (HR 0.84; 95% CI 0.79–0.90). Benefits from caffeinated coffee
Future directions
Recommendations are largely based on epidemiological studies subject to publication bias and confounding, and more high-quality randomized trials with longer follow-up are needed particularly in patients with pre-existing cardiovascular conditions. The long term safety of newer beverages with higher concentrations of caffeine and greater calorie content require further clarification.
Genetic variations in Cytochrome P450 enzyme 1A2 (CYP1A2), the enzyme responsible for 95% of caffeine metabolism,
Conclusion
Mild-to-moderate habitual consumption of caffeinated beverages, particularly a daily intake of 2–3 cups of coffee or tea, appears to be safe across a broad range of cardiovascular conditions, and may even be beneficial with respect to diabetes mellitus, atherosclerosis, heart failure, arrhythmia and total mortality. Acute consumption of high doses of caffeine, particularly in the form of energy drinks is best avoided.
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Funding Sources/conflicts of interest: Dr. Voskoboinik is supported by co-funded NHMRC/NHF post-graduate scholarships & Baker Bright Sparks scholarships. This research is supported in part by the Victorian Government's Operational Infrastructure Funding.
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