One of the biggest risk factors for COVID and especially for poor outcomes is Vitamin D deficiency, but this study apparently didn't even check Vitamin D levels. That seems like a serious oversight.
But what you can do in this study, is have a dataset with a good size (4m people from the UK!) which allows for much broader analysis than would be possible through other means.
Blood testing 4m people during a pandemic is impractical, and widescale self-reporting will provide insights not otherwise available (as this paper shows).
On at least two occasions China has swab-tested 10 million people in a single city within a week, when covid re-occurred in a city where it had been thought to be extirpated. I don't think blood testing is twice as difficult as swab testing. So, I don't think it's impractical per se. It's just impractical in the UK.
You know what's impractical? 2.7 million people dying and an unknown fraction of the survivors suffering disabilities and injuries such as diabetes, heart attacks, and cerebrovascular attacks.
That’s different to focusing resources on doing vitamin D testing for a speculative study to determine if there is a link between vitamin D and long Covid.
I’m just saying that given limited resources during this global pandemic, the best use of resources at present probably isn’t monitoring 4 million people’s vitamin D levels for this specific study.
I’m also saying that not every study has to study every possible factor - in fact this is almost impossible to do! This is a brilliant dataset of millions of people self reporting, and there are things that you can find with self reporting that you can’t find with blood testing (and visa versa). This is why other papers will do a literature review to compile together the results of multiple studies to understand the impact.
Is it? How exactly is vitamin D deficiency measured and diagnosed? How much variance / tolerance is there between people. Most importantly does COVID impact Vitamin D levels?
This may be a serious oversight. Or it may be that the Vitamin D thing is pseudoscience.
Yes
> How exactly is vitamin D deficiency measured and diagnosed?
Usually with a blood test. It's diagnosed because the blood test comes back out of range which is usually below 30 ng/ml for insufficiency, and below 20 for a deficiency.
> How much variance / tolerance is there between people?
The std. deviation is 16.6 ng/ml
> Most importantly does COVID impact Vitamin D levels?
I don't think we know, it's hard to track this. You'd need to follow a huge cohort of people who you test for vitamin d often enough so that while they're getting the infection we see their vitamin d in real time.
Yes, in the usual sense medical researchers use the term "risk factor", e.g., having a heart attack is a risk factor for having one of your great-grandparents die of a heart attack. Taking vitamin D probably won't reduce your covid risk, but it might, and it's a low-risk intervention that probably isn't harmful, so you should do it anyway unless you have some contraindication such as a high risk of kidney stones. The best review I've seen of the research literature is this post:
https://astralcodexten.substack.com/p/covidvitamin-d-much-mo...
(That post isn't medical advice, but this comment clearly is.)
AIUI, VitD is involved in T-cell production and so is needed to maintain our immune systems.
This is our course not medical advice.
So your knee jerk reaction is strictly speaking true yet also a distraction.
[0] https://pubmed.ncbi.nlm.nih.gov/31454046/
"Conclusions and relevance: Among healthy adults, treatment with vitamin D for 3 years at a dose of 4000 IU per day or 10 000 IU per day, compared with 400 IU per day, resulted in statistically significant lower radial BMD; tibial BMD was significantly lower only with the 10 000 IU per day dose. There were no significant differences in bone strength at either the radius or tibia. These findings do not support a benefit of high-dose vitamin D supplementation for bone health; further research would be needed to determine whether it is harmful."