This 2021 study "Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness" by Amiel A. Dror et al. reports:

Of the 253 individuals with pre-infection VitD levels, 133 (52.5%) had a level less than 20 ng/mL, 36 (14.2%) had 20 to less than 30 ng/mL, 44 (17.3%) had 30 to less than 40 ng/mL, and 40 (15.8%) had 40 ng/mL or greater (Table 1). Mortality among patients with sufficient VitD levels was 2.3%, in contrast to the VitD deficient group’s 25.6% mortality rate (p-value<0.001)

They also claim that they examined if the vitamin D defiency was a symptom of another illness which could have lead to these increased mortality rates and found that this was not the case.

They apparently linked other things to high mortality rates as well but nothing had a p-value this significant. Is this a case of trying to measure a lot of things and try to see what sticks (If anyone could tell me the name of this phenomenon as well that would be appreciated) or is this a robust study?

(Question structure inspired by this)

  • How am I allowed to edit this question? Commented Feb 10, 2022 at 12:35
  • @SamGinrich There should be an "Edit" button visible under the question. Click that and you can edit the question. Since you have less than 2k reputation, your edit will need to be approved, but as long as it's constructive and improves the question, that should be a formality.
    – F1Krazy
    Commented Feb 10, 2022 at 15:13

1 Answer 1


Out of interest, a Cochrane review from last year found the following:

There is currently insufficient evidence to determine the benefits and harms of vitamin D supplementation as a treatment of COVID‐19. The evidence for the effectiveness of vitamin D supplementation for the treatment of COVID‐19 is very uncertain. Moreover, we found only limited safety information, and were concerned about consistency in measurement and recording of these outcomes.

I couldn't find any reference to the Dror preprint that the OP asked about in the Cochrane review. However, the number of participants in all the studies assessed by the Cochrane (less than a thousand) appears to be of the same order of magnitude as that in the Dror study.

  • 4
    The Cochrane review was published a couple weeks earlier, so it's not surprising he doesn't mention Dror et al. Also, Dror et al looks at low vitamin D levels as a risk factor in contracting severe covid-19, while Stroehlein et al (the Cochrane paper) are focused on using vitamin D as a post-infection treatment. Commented Feb 4, 2022 at 16:21
  • @Cristobol Polychronopolis: ah thanks, so the Cochrane review is not looking at mortality, but rather treatment.
    – paddyr
    Commented Feb 4, 2022 at 16:47
  • 1
    It did take into account mortality. The difference is that Stroehlein et al (the Cochrane paper) is investigating whether vitamin D is effective as a treatment after infection, while Dror et al is looking at the effects of vitamin D level before infection as a risk factor for serious disease. Commented Feb 4, 2022 at 18:59
  • There's some confounding, since the elderly are more likely to be Vitamin D deficient. Commented Feb 10, 2022 at 23:58
  • 1
    Vitamin D in reasonable doses is generally good for you. In unreasonable doses it can be bad to very bad or even lethal. My understanding is that Covid treatment today means "keep the person alive until their immune system beats Covid", so having a reasonable amount of Vitamin D will give you a tiny advantage. It's cheap, so if it makes you feel better, and you don't go for an unreasonable dose, take it. Now if you are so Vitamin D deficient that it affects your health anyway, that might very well make Covid more dangerous.
    – gnasher729
    Commented Jan 26, 2023 at 9:53

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