Cardiovascular Effects of Coffee - Is It a Risk Factor?
Authors: Isabella Sudano, Christian Binggeli, Lukas Spieker, Thomas Felix Lüscher, Frank Ruschitzka, Georg Noll, Roberto Corti
DOI / Source: https://doi.org/10.1111/j.0889-7204.2005.02477.x
Date: 2005
Reading level: Beginner
Why This Matters for Freedivers
Coffee isn’t automatically “good” or “bad” for freediving, but it can nudge your physiology: it may raise blood pressure and change heart rate via autonomic reflexes, especially if you’re not a regular coffee drinker. For dive days, the practical takeaway is to avoid experimenting with high doses, and to remember that caffeine can also harm sleep — and poor sleep can quietly reduce performance and safety more than the coffee helps.
Synopsis
Coffee feels like a simple pre-dive ritual for many people — a warm cup, a mental boost, maybe even a “performance edge.” This review looks at what coffee (mainly caffeine) actually does to the cardiovascular system, and the answer is: it depends a lot on dose and whether you’re a habitual coffee drinker. People who don’t drink coffee regularly tend to feel stronger cardiovascular effects, while regular drinkers develop noticeable tolerance, meaning the same coffee produces smaller changes. 
The authors explain that caffeine blocks adenosine receptors, which tends to cause vasoconstriction (narrowing of blood vessels) and an increase in peripheral resistance. Practically, this often shows up as a rise in blood pressure, especially diastolic pressure. Interestingly, moderate doses can actually lower resting heart rate a bit — not because caffeine is “calming,” but because blood pressure rises and your baroreflex applies a vagal “brake” to slow the heart. With higher doses, heart rate can increase, and in people who are sensitive (especially non-habitual drinkers), high doses of caffeine/methylxanthines can contribute to palpitations and may trigger arrhythmias in predisposed individuals. The review notes that the most obvious BP/HR effects tend to fade within about an hour as caffeine levels change. 
Beyond the heart, the paper flags two points that matter for training and diving days: coffee can affect sleep quality (even if taken 30–60 minutes before bedtime, it can worsen sleep and delay sleep onset), and it can slightly stimulate breathing by increasing central sensitivity to CO₂, raising respiratory rate. It also briefly mentions coffee’s metabolic effects (glucose/insulin, free fatty acids) and that some population studies show mixed or even protective associations for certain diseases — but the main focus here is the acute cardiovascular response and the idea that regular use changes how strong that response is.