“Proteins are a diverse group of large, complex molecules that are crucial to every aspect of the body’s structure and function.” “Collagen, which forms the structural scaffolding of skin and many other tissues, is a protein.” “Insulin, a hormone that regulates blood sugar, is a protein”. “Trypsin, an enzyme involved in digestion, is a protein.” “So is the pigment melanin, which gives hair and skin its color.” “Still other proteins regulate the body’s production of proteins.”
So to answer your question we now know that one function of Vitamin D “turns genes off and on”. So not having enough Vitamin D would then cause dysfunction in the gene and not allow crucial proteins to be made. After that without the necessary proteins we then develop things like diabetes, thyroid problems and a host of other diseases.