Arrhythmia after caffeine in athletes: causes and the link with exercise load and pharmacology

The feeling of “skips” or a “pause” in the heart after a cup of coffee or a pre-workout formula is familiar to many athletes. At the same time, large studies of recent years show that moderate coffee consumption does not raise the risk of arrhythmias. The editorial team examines how to reconcile these facts, what exactly happens to the heart and why the risks are concentrated around high doses, energy drinks and combinations of stimulants.

How caffeine acts on the heart

The main mechanism of caffeine’s action is the blockade of adenosine receptors. In the heart, adenosine slows conduction through the atrioventricular node and reduces automaticity, so blocking it produces the opposite effect. In addition, caffeine raises the level of catecholamines in the blood and enhances sympathetic activity.

At high concentrations, well above the usual dietary ones, caffeine also inhibits phosphodiesterases and affects the release of calcium from the sarcoplasmic reticulum. It is precisely these changes in calcium metabolism in cardiomyocytes that are regarded as one of the mechanisms of triggered activity underlying extrasystoles.

In people who regularly drink coffee, partial tolerance to the haemodynamic effects develops: the rise in blood pressure and pulse after the usual dose becomes smaller. In those who consume caffeine only occasionally, the reaction is more pronounced. This explains why the same dose affects different people differently.

The rate of caffeine elimination depends largely on the CYP1A2 enzyme in the liver. There are known genetic variants that determine “fast” or “slow” metabolism. Smoking speeds up elimination, while hormonal contraceptives, pregnancy and some drugs (for example, fluvoxamine, ciprofloxacin) slow it, prolonging the action of caffeine.

What the research says: coffee and arrhythmia

For a long time doctors advised patients with arrhythmias to give up coffee. However, large population studies did not confirm this advice. An analysis of UK Biobank data (Kim et al., 2021), covering hundreds of thousands of participants, showed that moderate coffee consumption was associated with a slightly lower, not higher, risk of tachyarrhythmias, and Mendelian randomisation revealed no causal link.

The randomised CRAVE trial (Marcus et al., 2023), with continuous ECG monitoring, gave a more nuanced picture. On days when participants drank coffee, the number of atrial extrasystoles did not change, while the number of ventricular extrasystoles rose. At the same time, participants moved more and slept less.

Extrasystoles — premature contractions of the heart — occur in almost all people and are, as a rule, benign. It is these that most people feel as “skips” or a “jolt” in the chest. A frequent sensation of extrasystoles after caffeine usually does not mean a dangerous arrhythmia, but requires assessment if they are very frequent or combined with other symptoms.

Review articles (Voskoboinik et al., 2018) conclude that ordinary caffeine consumption does not provoke atrial fibrillation and ventricular arrhythmias in most people, yet some patients note a clear individual dependence. For them, individual observation matters more than average population data.

Features of athletes: doses, exertion, energy drinks

The position of the International Society of Sports Nutrition (ISSN, 2021) describes ergogenic doses of caffeine in the range of 3–6 mg per kilogram of body weight, taken about an hour before exertion. For a person weighing 80 kg this is 240–480 mg — more than two or three cups of coffee, and often in a single dose.

During intense exertion, sympathetic activity is already maximal, and to it are added electrolyte shifts, a rise in body temperature and catecholamine levels. A large dose of caffeine is layered onto this background. The period right after a workout is especially vulnerable, when tone switches quickly and the preconditions for extrasystoles arise.

Energy drinks and pre-workout formulas are a separate risk category. Besides caffeine, they contain taurine, guarana (an additional source of caffeine), synephrine, yohimbine and other substances. A review of reported cardiovascular events after energy drinks (Goldfarb et al., 2014) included arrhythmias, in particular atrial fibrillation, in young people, often in combination with alcohol or physical exertion.

Finally, athletes sometimes combine caffeine with other “cutting” agents: ephedrine, clenbuterol, thyroid hormones. Such combinations enhance sympathetic stimulation cumulatively. Clenbuterol and ephedrine are banned by WADA, and their combination with caffeine has been described in clinical reports of poisoning.

Who is at increased risk

People with already diagnosed arrhythmias, Wolff–Parkinson–White syndrome, long QT syndrome or cardiomyopathies must discuss caffeine and stimulant use with a cardiologist. For them, even doses that are ordinary for others can be a trigger.

Users of anabolic steroids and other hormonal drugs have an altered “substrate” — a hypertrophied myocardium, raised blood pressure, possible electrolyte disturbances. Against such a background stimulants become more dangerous, and the appearance of new symptoms should be a reason for examination.

Teenagers and young athletes with a small body mass receive a higher dose of caffeine per kilogram from the same can of an energy drink. Regulators in many countries recommend that children and teenagers do not consume energy drinks.

Finally, those who combine caffeine with a low-calorie diet, dehydration and sleep deficit during “cutting” or making weight before competitions are in the risk zone. It is precisely during this period that the electrolyte balance is most unstable.

• Diagnosed arrhythmias or channelopathies.
• Structural heart disease, including against the background of AAS.
• Small body mass and adolescent age.
• Simultaneous intake of other stimulants or drugs that slow caffeine metabolism.
• Making weight, dehydration, sleep deprivation.

Practical conclusions on consumption

For healthy adults EFSA considers up to 400 mg of caffeine per day and up to 200 mg in a single dose to be safe. An ergogenic effect was obtained in studies at lower doses too, around 3 mg/kg, so chasing maximum doses often makes no sense in terms of results.

It is worth counting caffeine from all sources: coffee, tea, energy drinks, pre-workout formulas, “fat burners”, gels. If a product does not state the exact amount of caffeine per serving, the editorial team advises refraining from it.

If “skips” appear only after caffeine, a simple test is to exclude it temporarily and then cautiously reintroduce small doses. However, this does not replace an examination if symptoms are pronounced, frequent or accompanied by dizziness.

We cover diagnosis, prevention and alarming symptoms in detail in a separate material. We also recommend reading the articles on tachycardia in athletes and on caffeine as an ergogenic aid.

Editorial conclusions

In most people moderate coffee consumption does not increase the risk of dangerous arrhythmias, and large studies even show a neutral or favourable link.

The sensation of skips after caffeine is most often linked to benign extrasystoles, whose number may rise after coffee, especially ventricular ones.

The risks are concentrated around high single doses, energy drinks, pre-workout blends, powdered caffeine and combinations with stimulants and hormones, as well as against a background of dehydration and existing heart disease.

Individual reaction matters more than average figures: if the heart “responds” to caffeine, it is worth reducing the dose and getting an examination.

References

1. Marcus GM, Rosenthal DG, Nah G, et al. Acute effects of coffee consumption on health among ambulatory adults. N Engl J Med. 2023;388(12):1092–1100.
2. Kim EJ, Hoffmann TJ, Nah G, et al. Coffee consumption and incident tachyarrhythmias: reported behavior, mendelian randomization, and their interactions. JAMA Intern Med. 2021;181(9):1185–1193.
3. Voskoboinik A, Kalman JM, Kistler PM. Caffeine and arrhythmias: time to grind the data. JACC Clin Electrophysiol. 2018;4(4):425–432.
4. Guest NS, VanDusseldorp TA, Nelson MT, et al. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021;18(1):1.
5. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the safety of caffeine. EFSA J. 2015;13(5):4102.
6. Goldfarb M, Tellier C, Thanassoulis G. Review of published cases of adverse cardiovascular events after ingestion of energy drinks. Am J Cardiol. 2014;113(1):168–172.
7. World Anti-Doping Agency. Prohibited List. Montreal: WADA; чинна редакція.