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I was surprised by the lack of correlation between caffeine intake and sleep quality, but the takeaway, for me, is that if they were specifically looking into that, they’d need to control for other factors. And n=5 is pretty small.
Interesting stuff.
And you would need to include exteme cases to make the effects visible. Having two cups a day might not be enough, and 4 might just approach the limit. People who drink like 10 cups a day should stand out in a study like this.
You could maybe work this out from a meta analysis of the studies about caffeine and focusing, where the control group is actually just in withdrawal.
Maybe? I was surprised to hear James saying he hadn’t had any caffeine on multiple days.
One coffee a day? Those are rookie numbers!
Joking aside, that could mean there’s already significant variance in their intake.
I drink about two cups a day (400 ml in total), and I definitely get a headache if I drop my caffeine intake too suddenly. If I was adapted to drinking much less, then I might be able to go an entire day without noticing anything, but at the current level, it’s just not going to happen. Did James mention how much coffee do the participants normally drink every day? If they are all in the 1 cup club, these results are only exploring one extreme of the scale.
I think their normal intake was 4 or 5 coffees. I’d expect to feel **something ** cutting down from that to 0. Maybe the decaf placebo really worked for them, most days?
Also, it will have been either a modest variation in caffeine intake, or else a variation in modest intake (e.g. adjusting intake say from 6->5, 2->1 or 1->0). These are people who've already stabilized their caffeine intake to not disrupt their lifestyle, and were just adjusting that sometimes to remove the first coffee of the day.