Vaccination has started and we can see some kind of horizon in this historical COVID-19 pandemic. I really think it is interesting that people, by the spread of the word, started to have vitamin D during this pandemic. I do not know from where it emerged since there is no direct evidence that vitamin D can hamper or prevent COVID-19 infection https://www.covid19treatmentguidelines.nih.gov/supplements/vitamin-d/.
I have browsed the literature, and there is already quite a lot written on a possible link between COVID-19 and vitamin D. Meta-analysises have been published. In a systematic meta-analysis you start with a lot of published scientific papers, you have specific inclusion criterias, select papers, and finally, some conclusions can be made from the scientific literature.

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This above is from Pereira et al 2020 and you can find the full review here Vitamin D deficieVitamin D deficience – historical reviewncy aggravates COVID-19 (Meta analysis). Interestingly, Pereira and collegues observed a positive association between deficiency of vitamin D and the severity of COVID-19 disease.
The exact mechanism of action on how vitamin D prevent, or possible help in treating COVID-19 is not known. However, it is known that vitamin D has some immunomodulatory effects that could potentially protect against a COVID-19 infection and/or decrease the severity of illness. Future clinical trials will help us to understand the role of vitamin D in preventing and treating COVID-19 and possibly other infections. This publication shows the plethora of the suggested immunomodulatory effects of vitamin D Exploring links between vitamin D deficiency and COVID-19.
In summary, to the best of my knowledge, supplement of vitamin D is beneficial for health in general if accurate dosages are used, especially during winter time due to lack of sun. The dosages of supplementary vitamin D vary between countries, and here you can find what the National Institute of Health in the USA recommends https://ods.od.nih.gov/factsheets/VitaminD-Consumer/.
Finally, I am ending this writing by sharing a historical review from 2008 on vitamin D Vitamin D deficience – historical review. For those who are interested, please read this review! Always good to refresh eg the origin of vitamin D like sunshine, toxicicity, role of. And so on.
Stay safe 🐾