A weak espresso sounds like you're just making a small amount of American/German coffee. How could that be passed of as an espresso? It's not just a measure of volume.

James Hoffman did some interesting videos on that -- espresso is a more efficient extraction method than Aeropress, but less complete than a very high water to coffee ratio pour over for the same weight of ground coffee. Extraction of caffeine is very directly tied to contact time and temperature, so two double shots of espresso (40g coffee) can actually be less caffeine extracted than a single large pour over (25g coffee) when the pour over is upwards of 22% extraction (typical of 20:1 water to coffee ratios and modern zero-bypass brewers). Similarly, there are large differences in beans, so 22% extraction on weak caffeine beans might be way less than 18% extraction on much higher caffeine beans. This is most obvious in the fact that Robusta has much higher caffeine on average than Arabica. Also, 22% extraction has a lot more unpleasant bitter compounds, not just more caffeine, so it's not my preference for taste in general.

It's probably whatever "1 cup" means to the patient. The researchers would want them to stick to their status quo for the best results.

For example, 1 cup of coffee for my wife involves a blend of coffee and espresso beans with no adders, but 1 cup to her dad means lighter roast bean with milk. Both options have different caffeine contents and nutritional values.

I researched this a bit and found there really is no standardized "cup of coffee" for research purposes. Even for volume, I've seen it range from 6 to 12 fl oz. The main mechanisms of action are caffeine and flavonoids, and there's so much variation across beans and brewing methods that you'd think researchers would try to include that in their data to normalize it.

They were advised to drink at least one cup per day IIUC / maintain their current lifestyle. So there is no consistent amount, but it’s still meaningful vs being advised not to have any caffeine.

> "1 cup of caffeinated coffee" basically says nothing at all

Frankly, no. 1 cup of caffeinated coffee is on average significantly more caffeine than 0 cups, which is all you need for sufficient n. The only confounding variable to worry about here is whether caffeine is entering the diets of the two experimental groups at different rates via other channels (e.g., are the people who are forbidden to drink coffee drinking more tea to compensate?), though even this effect, if present, would likely tend to decrease the separation of the outcome distributions and is thus a low threat to validity.

People obsess over precision when it is often one of the least important aspects of an experiment. The outcomes of studies like this are in practice absolutely dependent on quality and rates of compliance. Choosing an uncomplicated treatment that is easy and natural for subjects to comply with is not merely acceptable but in fact a massively better design than complex protocols involving precisely measured quantities of lab-grown coffee in vials that can be misplaced, forgotten, deliberately shunned, etc. Also in this case the treatment corresponds closely to the real-world situation that the research is attempting to learn about.

There’s an average amount in the average cup of coffee.

To add more information, the intervention was guidance about caffeine intake. From the Methods:

> If allocated to caffeinated coffee consumption, patients were encouraged to drink at least 1 cup of caffeinated coffee (or at least 1 espresso shot) and other caffeine-containing products every day as per their usual lifestyle. It was recommended that patients in the coffee consumption group not intentionally increase or decrease consumption of coffee or other caffeine-containing products.

> If allocated to the abstinence group, patients were encouraged to completely abstain from coffee, including decaffeinated coffee, and other caffeine containing products.

The people who were selected into the study were not necessarily "habitual coffee drinkers". The only requirement was "was a habitual coffee drinker sometime in the past five years". The difference between the two is subtle, but its possible there were people in the study who had already abstained for some amount of time.

Cardiologists pride themselves on the best acronyms in study titles I think. There's a lot of good ones out there.

Have you compared any other factors? I find that my most consistent factor for a-fib is dehydration.

Me too, less caffeine means less stress and anxiety for me.

The key is to find other warm beverages to drink and get protein and sugar into you in the morning.

We've been loving Golden Lattes!

Note that study suggests that coffee consumption decreases arrhythmia. (The title is horribly confusing, I know.)

From a quick skim, the protocol seemed to be “advise the patient to drink at least one cup of coffee per day or continue drinking your usual amount.” So it seems the results don’t track with your experience (or my own experience of improved stress and happiness when I cut down on coffee) which is why I think it’s surprising / possibly a fluke.

I've found great difference in how I feel based on the source of caffeine.

From best to worst, for me: Yerba mate > healthi-ish energy drinks > white/green/black tea > coffee.

Coffee almost always results in significant anxiety (at same caffeine dose), jitteriness, and acid reflux. Yerba mate is by far the best for me.

I definitely get a skipped beat arrhythmia when I’m hung over. Noticed it in my 30s. 15 years of amphetamine use prob didn’t help. Thankfully I only drink when I’m single, so I’ve had a nice break.

Weird story: I bought a Kardia when I was having mystery arrhythmia. At its worst, a half cup of coffee would trigger it, but at that point I suspect the anxiety of getting it was also a trigger.

It was caused by a minoxidil+finasteride spray I was applying to my head for a year. It slowly got worse over time so it took me way too long to suspect it.