Headlines: vegetarian diets prevent severe COVID!

Study: cross-sectional survey-based investigation of an online sample of healthcare workers shows some interesting associations

The headlines are wildly silly 1/n
2/n The study is here, and fun for a quick read. Basically, a group of researchers surveyed healthcare workers in July-Sept 2020 and asked them stuff about their diet and COVID nutrition.bmj.com/content/early/…
3/n This appears to be the 3rd or 4th study published from that survey. The authors basically found that, after controlling for a couple of confounders, there was an association between self-reported diet and risk of severe COVID-19
3.5/n (As a minor bugbear, the authors report this as a case-control study but that's not true because they didn't identify their participants based on COVID-19 status they just recruited healthcare workers to do their survey so it should be called a cross-sectional cohort)
4/n Anyway, regardless of the study type, it definitely doesn't support the headlines

Firstly, there's the population. This study was almost exclusively comprised of middle-aged, white doctors
5/n We can quibble about generalizability, but as a general rule if ~80% of your population is a single very specific demographic, it's hard to say much about populations based on that sample
6/n Secondly, there's the issue with unmeasured confounding. The study only asked people about a small number of covariates, but there are ~dozens~ of potentially important things that this could've missed
7/n Ignoring the obvious things like income, we might be worried that level of exposure to COVID-19 cases could cause people to have a higher risk of COVID-19, but that information wasn't included in the model
8/n There's also some indications in the study itself that the survey data (collected online) might not be very good as well

For example, of the 568 people who report having COVID-19, 33% say that they had a NEGATIVE COVID-19 test
8.5/n This may have been because the definition of a COVID-19 'case' used in the study is very broad. It appears that anyone with any symptoms consistent with COVID-19 would be a case here, regardless of testing
9/n When the researchers excluded these PCR-negative cases from their model, the statistically significant association between vegetarian diets largely disappeared 👀👀👀
10/n Anyway, the headlines saying that vegetarian diets reduce the risk of severe COVID-19 are rather ridiculous. This study just can't prove that
11/n A better headline might be "middle-aged white doctors who report eating vegetarian diets at slightly reduced risk of reporting COVID-19 symptoms, study suggests"

Not quite as impressive, perhaps, but a bit more accurate
12/n Oh, also, forgot to mention that the headline "73%" reduced risk is a relative risk, if you calculate the absolute risk difference for severe COVID-19 between the vegetarians and everyone else it works out to be about 4% so there's that too

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More from @GidMK

8 Jun
@jamesheathers and I have an important new piece out in STAT today talking about science during The Plague

Bottom line - academic science has not come out of the pandemic looking good

statnews.com/2021/06/08/sci…
The simple fact is that our current system for generating and correcting evidence has not handled the incredibly tight timeframes of Covid in any reasonable way
I think this story about a paper in Scientific Reports exemplifies the issue

The authors and editors did everything RIGHT as far as traditional academia goes. And yet, it was a massive failure in many ways
Read 6 tweets
4 Jun
If you want to consider the travesty of medical advice vs evidence during COVID-19, vitamin D is an amazing example

100s of millions of people have self-medicated/been treated with vit D for COVID. The evidence base is trash
A living Cochrane systematic review last updated May 2021 gives you an idea of this - as of 14 months into the global pandemic, there are 3 published RCTs on vitamin D

<400 total patients

cochranelibrary.com/cdsr/doi/10.10…
And look, it's never been tremendously likely that vitamin D was the key ingredient to banishing COVID-19, but it is wild that so many people have taken it for the disease and we still don't even know if there are harms to that or not
Read 5 tweets
2 Jun
This is one of my favourite things of the year

People on Tiktok are drinking lettuce water because of a rumour it helps you sleep

This is all apparently based on a 2013 study that looked at lettuce leaf/seed extracts IN MICE @justsaysinmice Image
Now, I should say that the original rumour that started on Tiktok may not be entirely due to this study. The Pedestrian article says that this is the research backing up the claim, but there's no evidence that's true Image
Nevertheless, this study is BRILLIANT:

- extracted substances from lettuce leaf/seeds
- gave extract to mice
- sedated mice
- measured sleep times (slight difference)
Read 8 tweets
30 May
A "new study" has hit the headlines that apparently proves that SARS-CoV-2 was lab-grown

I am QUITE SKEPTICAL for a number of reasons, would love your thoughts...
First massive red flag🚩: the paper is NOT PUBLISHED YET

Science journalists know you NEVER report on a paper that is unpublished (because it might be shit)
Second 🚩🚩🚩: the abstract is...kind of weird

I'm not a virologist, but talking about some previous experiments that "reverse the burden of proof" is...not really logical
Read 7 tweets
27 May
An interesting new study - systematic review and meta-analysis for ivermectin. Found:

- no benefit for all-cause mortality
- no benefit for length of stay

Both very low-quality evidence
medrxiv.org/content/10.110…
I haven't had time to read it in extreme detail yet, but a quick skim seems to show that it is a fairly good piece of research that the authors have already improved in the 24 hours since it went online
Arguably the most important point of the study - the vast majority of evidence on ivermectin for COVID-19 appears to be of extremely poor quality even when you limit the results only to the best studies
Read 5 tweets
27 May
This is a bizarre take. The evidence has stayed precisely the same - natural origin very likely, lab leak thus far entirely unproven and a very low chance

The rest is mostly misconceptions caused by reading only sensationalist headlines
There is an excellent and comprehensive thread on the issue here, but the basic point is that experts pretty much universally agree that a natural origin is by far the most likely explanation
It is POSSIBLE that there was a lab leak and THIS SHOULD BE INVESTIGATED, but it is also only a very SMALL possibility and certainly not more likely than a natural explanation
Read 7 tweets

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