The vitamin B-complex are essential water-soluble vitamins, including vitamin B1(thiamine), vitamin B2 (riboflavin ), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), biotin, folic acid and vitamin B12 (cobalamins). A. Vitamin B1 (Thiamine) Vitamin B1 and various diseases of the gastrointestinal tract The measurement of vitamins C and B1 content in the blood …