B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism. Though these vitamins share similar names, research shows that they are chemically distinct vitamins that often coexist in the same foods. In general, supplements containing all eight are referred to as a vitamin B complex. Individual B vitamin supplements are referred to by the specific name of each vitamin (e.g., B1, B2, B3 etc.).

1. Aamir Ali Khan
M.Phil Biochemistry
Head of Pathology Department
Northwest Institute of Health sciences

2. Vitamins Classification Chart

3. Vitamins
• Water-soluble
– Thiamine
– Riboflavin
– Niacin
– Pyridoxine
– Biotin
– Folic acid
– Cobalamin
– Ascorbic acid
– Pantothenic acid
• Fat-soluble
– Vitamin A
– Vitamin D
– Vitamin K
– Vitamin E

4. Thiamine B1
• Vitamin B1
• Biologically active form
– thiamine pyrophosphate (TPP)
– Also can have TTP
• Function
– cofactor in oxidative decarboxylation of a- keto acids (TCA, AA degradation)
– RC(O)COOH to RC(O)OH + CO2
– Other coenzymes also involved in process
• Sources
– pork, whole grains, legumes, tuna, soy milk
• RDA
– 0.5 mg/1000 Cal intake or min 1 mg/day
• Deficiency
– decreased ATP production
– impaired cellular function
– Beriberi

5. Riboflavin B2
• Vitamin B2; vit G?
• Biologically active forms
– Flavin mononucleotide (FMN)
– Flavin adenine dinucleotide (FAD)
• Function
– Electron transfer
– FMNH2, FADH2
– Redox reactions (TCA, glycolysis, etc.)
– Needed for good vision and healthy skin
• Sources
– Milk, mushrooms, tomatoes, liver, green leafy vegetables
• RDA
– 1.1-1.3 mg/day
• Deficiency
– Growth retardation
– Ariboflavinosis
• Glossitis (Glossitis can mean soreness of the tongue).
• Stomatitis (Stomatitis is inflammation of the mouth and lips)

6. Niacin B3
• Biologically active forms
– NAD+, Nicotinamide adenine dinucleotide
– NADP+
– Nicotinamide (readily deaminated, also in diet)
• Function
– Coenzymes in redox reactions (TCA, FA synthesis, gluconeogenesis, etc.)
– DNA repair
• Sources
– Unrefined grains, fortified cereal, meat, fish, tomatoes, mushrooms, milk,
liver, rice
– Metabolism of tryptophan when AA is abundant (needs riboflavin and B6)
• RDA
– 14-16 NE/day (NE = niacin equivalents = 1 mg niacin or 60 mg
tryptophan)
• Deficiency
– Pellagra = “rough skin”
• Toxicity
– Skin inflammation, heartburn, nausea, liver damage

7. Pyridoxine B6
• Vitamin B6, pyridoxal, pyridoxamine
• Biologically active form
– pyridoxal phosphate (PLP)
• Function
– Coenzyme for transamination reactions, esp. AAs (neurotransmitters)
– Decarboxylation of carboxylic acids
• Sources
– Wheat, corn, egg yolk, liver, potato, banana, fish, chickpeas
• RDA
– 1.3-1.7 mg
• Deficiency
– Induced by TB drug isoniazid (supplement given)
– Dermatitis, fatigue
– Depression, confusion
– Convulsions, seizures
– Microcytic hypochromic anemia
– Epidemic in 1950s
• Toxicity
– Neurological disorders at > 2 g /day

8. Biotin B7
• Biologically active form
– Binds to lysine residue of enzyme
• Function
– Cofactor in carboxylation reactions, carrier of CO2 (acetyl-CoA to
malonyl-CoA, synthesis of fatty acids)
– Regulation of gene expression
• Sources
– Almost all food, esp. milk, egg yolk, tomato, almond, peanuts, avocado,
mushroom
– Also synthesized by intestinal bacteria
• RDA
– At least 30 mg/day
• Deficiency
– Deficiency does not occur naturally unless eat 20 raw egg whites per day
(protein avidin binds biotin irreversibly and excreted)

9. Folic acid
• Biologically active form
– Tetrahydrofolate (THF)
• Function
– Stimulates digestive acids; appetite
– Receive one carbon fragments from donors and transfer them in AA synthesis
and nucleotide synthesis
• Sources
– Green leafy veggies (“foliage”), organ meats, legumes, okra, whole grain cereals
• RDA
– 400 mg/day, more during pregnancy and lactation
• Deficiency
– Megaloblastic /macrocytic anemia and growth failure
– Once, most common vitamin deficiency in US; now fortified cereals
– Absorption inhibited by many medicines, so a problem with the elderly

10. Cobalamin 12
• Vitamin B12
– Corrin ring system with Co in center (Corrin is an heterocyclic compound. It is
the parent macrocycle related to substituted derivative that is found in vitamin
B12. Its name reflects that it is the "core" of vitamin B12)
• Function
– Synthesis of Met
– Methylmalonyl-CoA to succinyl-CoA
• Degradation of odd-chain FA, enter TCA
– Transfer of methyl groups
– Produce red blood cells
• Sources
– Liver, whole milk, cottage cheese, oysters, salmon, clams, eggs, shrimp, pork,
chicken (animal sources)
• RDA
– 2.4 mg/day
• Deficiency
– Caused by pernicious anemia
– Methylmalonic acidemia (MMA)