Hi Katonargh, a warm welcome to the site. Can you please provide a link to your source of information about a lack of Vitamin D & it being responsible for asthma.
Whilst there's professional interest in vitamin D, as far as I know there's not yet any proven association between the 2, asthma is a defensive reaction that happens within the 'wind pipes' to a range of stimulants/triggers including environmental factors such as air-born allergens -
what is asthma on asthma.org.uk and on
NHS choices
Vitamin D does have a direct impact on bone development & growth. A deficiency or lack of Vitamin D can contribute to the development of rickets which softens bones, resulting in their malformation -
google image search
Vitamin D, calcium and rickets on NHS.uk
Best wishes with your study