Explanation:

There have been considerable discussions in scientific circles on the importance of vitamin D in these days of the COVID-19 pandemic.
How is Vitamin D produced?

• It is produced when sunlight (or artificial light, particularly in the ultraviolet region of 190-400 nm wavelength) falls on the skin and triggers a chemical reaction to a cholesterol-based molecule, and converts it into calcidiol in the liver and into calcitriol in the kidney.
• Vitamin D is a fat-soluble vitamin, meaning that it dissolves in fats and oils and can be stored in your body for a long time.

Its role:

• It is known to help in having the right amount of calcium in the bones, catalyse the process of protecting cell membranes from damage, preventing the inflammation of tissues and helping stop tissues from forming fibres and weakening bones from becoming brittle, leading to osteoporosis.

Concerns now:

• Vitamin D deficiency can affect COVID-19 high-risk patients, particularly those who are diabetic, have heart conditions, pneumonia, obesity and those who smoke.
• It is also associated with infections in the respiratory tract and lung injury.

Hence all statements are correct.