Water-soluble vitamins are soluble in the blood and minimally stored in the body, unlike fat-soluble vitamins. The most clinically important water-soluble vitamins include vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folate), vitamin B12 (cobalamin) (the last 2 being some of the most clinically important vitamins and discussed separately), and vitamin C (ascorbic acid). Many of these vitamins are critical components of different metabolic pathways and play important roles in normal cell function. Most are found in our daily diet, but some people with restrictive diets, malabsorptive conditions, or alcohol use disorder may present clinically with vitamin deficiencies and their consequences. Since they are water-soluble and excreted by the kidneys, most of these vitamins do not reach toxic levels.