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This is another pretty simple epidemiological study - take a large cohort of people, split them up by how much they nap, and see who's at a higher risk of heart diseasepic.twitter.com/9UzG6BDrG7
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Basically, the researchers found that people who napped 1-2 times a week had the lowest risk of cardiovascular events (heart disease), while those who napped 6+ times a week had the highestpic.twitter.com/B39pabnkZn
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However, after correcting for some fairly simple confounding variables, the relationship disappeared for the 6+ nappers, although the reduced risk for 1-2 per week nappers remained significantpic.twitter.com/oLYCbQzN8w
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However, something that wasn't reported on in the media is that the protective effect of 1-2 naps a week ENTIRELY DISAPPEARED when you controlled for Obstructive Sleep Apnea (OSA)pic.twitter.com/UFxsDf4Z9H
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In other words NAPS DIDN'T HAVE MUCH OF AN EFFECT AT ALL ONCE YOU CONTROLLED FOR OSA This was, surprisingly, relegated to a single sentence in the results and a somewhat incomplete explanation in the limitations section of the paperpic.twitter.com/WjbU5nFOdV
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It's plausible that the relationship was attenuated because of the reduced sample size It's also plausible that it was attenuated because OSA causes people to nap and it's an example of classic confounding/reverse causality
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On top of this, there was ENORMOUS potential for residual confounding in this study For one thing, even the controls for confounding were based on some pretty simple variables (probably due to the sample itself)pic.twitter.com/gHPw2E6zZM
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If nothing else, the fact that there were no controls for alcohol and drug use, which might impact both napping and CVD risk, makes the results quite challenging to interpretpic.twitter.com/1UekGHmQ2C
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The authors acknowledged most of this in their limitations, because it's all fairly basic epidemiological stuff and they're clever scientistspic.twitter.com/IhZ0CJvxTR
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But when you get to the press release, somehow much of the message that this potentially might not have anything to do with naps at all is lostpic.twitter.com/UtJ7RPNzyG
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And then the headlines - especially the totally ridiculous "a nap can save your life" - are wildly off base
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TL:DR - Swiss people who nap a little might be slightly healthier than those who don't nap at all - Might be more to do with age and OSA than naps themselves - No good reason to believe that naps are healthy
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Also, forgot to mention, the relative risk decrease was large (50%!) but the absolute risk decrease for napping was more like 3% which is a bit less impressive
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