Vitamin D is fat soluble vitamin and hormone too, its important for our immunity, diabetes, obesity, coronavirus, bone diseases and many other diseases, so intake of this vitamin or its deficiency can do multiple diseases, so sufficient quantity of this vitamin is essential daily from sunlight or dietary supplements or through available tablets/oral injections. laboratory test is also available for its diagnosis and we can tackle many diseases through this vitamin,.
https://www.youtube.com/watch?v=9ZrjyEejKWE&t=348s