It was March or April when the NIH released a bunch of papers on diseases on either Kaggle or Github (can't exactly remember). I decided to dig into all the data for fun ("fun", it was all in json and you had to manually parse the bitch to read it all). There's a fuckton (in the scientific sense) of studies that show a really good relation to Vit D deficiency and generally being sick as shit (flu, URIs, sinus infections, gastro problems, etc). While Vit C might be good for recovering, D is what you want to focus on in general disease prevention (a wide gamut at that). Outside of that 60k paper release, there are lots of studies on the mental health of folks regarding low and regular Vit D levels (low Vit D levels lead to more, worse and prolonged depression & anxiety).
What I've really taken away from this crazy year, why the hell is there all this research (decades worth, not a handful of years, I'm talking about roughly 40+ years worth) on good levels of Vit D levels leads to a statically healthy life and this fact is being completely shit on/ignored? Perfect? No. But, statistically speaking, you're sickly if your Vit D levels are low, regardless of Covid.
This is unrelated to my parent comment: perhaps I wasn't clear that being outside (in the sun) has a larger impact on your Vitamin D levels than supplementation.
Therefore the study's conclusion is invalid if the two groups studied were measured one before and one after lockdown kept them inside - since we would expect Vitamin D levels to drop, for this reason.
"low Vit D levels lead to more, worse and prolonged depression & anxiety"
This isn't entirely accurate, and I'm going to quibble a bit with it and cite a study, but TLDR exercising outside during the daytime is probably better than just supplements of D.
To be clear I myself take Vitamin D because it may have benefits, including for mental health, so this isn't me trying to say D couldn't help with depression, just that that particular statement is a little misleading in that we don't have the best evidence for it.
There's definitely some evidence that Vitamin D levels are correlated with worse depression scores, but no studies about deficiency causing it to be worse; I suspect few people would choose to sign up for a study to make they depression worse, tbh. Anyway, the closest are studies of supplements to Vitamin D levels in depressed people, and the results there are mixed.
For example a study called "Effect of vitamin D supplement on depression scores in people with low levels of serum 25-hydroxyvitamin D: nested case-control study and randomised clinical trial" in the British Journal of Psychiatry found no statistically significant differences in depression inventories.
I believe there is some meta analysis that shows that Vitamin D supplementation may benefit people with clinically significant depression scores. But if you are badly depressed, you should consider moderate mixed aerobic and anaerobic exercise outside during the day, which gets you sunlight for vitamin D, exercise, and light exposure.
Regardless of whether Vitamin D makes a difference, exercise and light exposure both can help with depression (or in the case of the latter at least Seasonal Affective Disorder, which can cause or exacerbate depression), and the evidence there is more substantial. For the record, light therapy boxes seem to help with SAD even when they generally have low UV so little chance that it's vitamin D that's making the difference.
