Which medical specialty will first look for deficiencies in vitamins to treat ailments from the root cause?

Unless you have spent the last year being held in a North Korean dungeon, sailing with Captain Bligh around the Cape and living on Hardtack, or you have had stomach stapling surgery, it is *HIGHLY* unlikely that you'll encounter any ailments cause by vitamin deficiencies. Just eat a normal diet, and try to include a wide variety of foods, to include quality proteins, citrus fruits and root veggies, and you won't have to be concerned about vitamin deficiencies. There are a VERY FEW disorders where vitamin treatment is essential, and they show up quickly on routine blood counts when the Lab Tech inspects the white blood cells. These are usually caught early in life, and do not require oral vitamins to treat. Vitamin B-12 deficiencies, for example, can only be treated by injection, not by taking expensive pills from the Chiropractor.