The varieties of language you use in different areas of your life are known as speaking or writing styles. Some particularly specialized styles, such as those used in the courtroom, or poetry, or the operating room, are known as registers.
The United States National Institutes of Health recommends testing vitamin A levels in people with celiac disease at diagnosis. This is because vitamin A deficiency is common in celiac disease. Deficiency can result from incomplete digestion, absorption, or metabolism. Normal absorption of vitamin A first requires digestion, or releasing, from food protein in the stomach.
But many people who avoid meat don't become deficient in vitamin B12. Many other foods, especially fish, contain vitamin B12. There are a couple of diseases that could cause low levels of vitamins D and B12. Celiac disease (gluten sensitivity) might cause vitamin and mineral deficiencies without specific symptoms. Crohn's disease could also cause both, but most people with Crohn's will have symptoms such as abdominal pain and frequent stools.