This was a large study, a total of 449 563 participants with an average age of 58 years with 55.3% females were followed for over 12.5 years (Chieng D, et.al., 2022).
This is what the researchers found. Ground and instant coffee consumption was associated with a significant reduction in arrhythmia at 1-5 cups per day but not for decaffeinated coffee.
Caffeine is not harmful unless it is consumed in excess as in the so-called energy drinks, or in case you are very sensitive to caffeine, then you need to be careful.
The lowest risk for arrhythmia was found for 2-3 cups per day for instant coffee and 4-5 cups per day for ground coffee. All coffee types were associated with a reduction in cardiovascular disease risk and all-cause mortality. The lowest risk was 2-3 cups per day even for decaffeinated coffee.
David Chieng 1 2 3, Rodrigo Canovas 4 5, Louise Segan 1 2 3, Hariharan Sugumar 1 2 3, Aleksandr Voskoboinik 1 2 3, Sandeep Prabhu 1 2 3, Liang Han Ling 1 2 3, Geoffrey Lee 3 6, Joseph B Morton 3 6, David M Kaye 1 2 7, Jonathan M Kalman 3 6 7, Peter M Kistler, The impact of coffee subtypes on incident cardiovascular disease, arrhythmias, and mortality: long-term outcomes from the UK Biobank, Eur J Prev Cardiol. 2022 Sep 27;zwac189.