Vitamin B12 is distinguished by its unique beneficial properties that play a major role in the proper functioning of the body. Interest in vitamin B12 began 2 centuries ago and it is still relevant to study its role. Vitamin B12 plays a special role in the proper functioning of the immune system. With increasing statistics in the autoimmune disease registry around the world (including the most common thyroid autoimmune disease), the interest in medicine is to determine the correlation between vitamin B12 and autoimmune diseases. Various studies have shown a correlation between them, although there is a little evidence for a link between vitamin B12 and autoimmune diseases of the thyroid gland.