For those who are not aware of how Vitamin D is important in the body, especially to the immune system, check out Dr Tim Smith on GcMAF, one of the body's immune system stimulants. It causes the macrophages--front line immune system troops--to be more active. Vitamin D is needed for the body to make GcMAF. Viruses and cancer make nagalese that damages the body's ability to make GcMAF. So this is a fight to the death. Either we make enough GcMAF to activate our immune system troops or viruses and cancer will disable our abilityu to make GcMAF.
http://gcmaf.timsmithmd.com/

This article is a better introduction into the basics of GcMAF.
https://www.naturalnews.com/SearchResults.asp?query=GcMAF+%2B++Vitamin+D&pr=NN

This issue is probably relevant for those who are concerned about the new Chinese virus. Since it will likely take a year for a vaccine to be ready, and who knows how helpful and safe the vaccine will be, people will need other methods for defending oneself from the virus' worst effects.

https://www.amazon.com/MIRACULOUS-RESULTS-EXTREMELY-SUNSHINE-EXPERIMENT-ebook/product-reviews/B005FCKN2S/ref=cm_cr_arp_d_viewopt_srt?ie=UTF8&reviewerType=all_reviews&sortBy=recent&pageNumber=1