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.).
3. Vitamins
โข Water-soluble
โ Thiamine
โ Riboflavin
โ Niacin
โ Pyridoxine
โ Biotin
โ Folic acid
โ Cobalamin
โ Ascorbic acid
โ Pantothenic acid
โข Fat-soluble
โ Vitamin A
โ Vitamin D
โ Vitamin K
โ Vitamin E
4. Thiamine B1
โข Vitamin B1
โข Biologically active form
โ thiamine pyrophosphate (TPP)
โ Also can have TTP
โข Function
โ cofactor in oxidative decarboxylation of a- keto acids (TCA, AA degradation)
โ RC(O)COOH to RC(O)OH + CO2
โ Other coenzymes also involved in process
โข Sources
โ pork, whole grains, legumes, tuna, soy milk
โข RDA
โ 0.5 mg/1000 Cal intake or min 1 mg/day
โข Deficiency
โ decreased ATP production
โ impaired cellular function
โ Beriberi
5. Riboflavin B2
โข Vitamin B2; vit G?
โข Biologically active forms
โ Flavin mononucleotide (FMN)
โ Flavin adenine dinucleotide (FAD)
โข Function
โ Electron transfer
โ FMNH2, FADH2
โ Redox reactions (TCA, glycolysis, etc.)
โ Needed for good vision and healthy skin
โข Sources
โ Milk, mushrooms, tomatoes, liver, green leafy vegetables
โข RDA
โ 1.1-1.3 mg/day
โข Deficiency
โ Growth retardation
โ Ariboflavinosis
โข Glossitis (Glossitis can mean soreness of the tongue).
โข Stomatitis (Stomatitis is inflammation of the mouth and lips)
6. Niacin B3
โข Biologically active forms
โ NAD+, Nicotinamide adenine dinucleotide
โ NADP+
โ Nicotinamide (readily deaminated, also in diet)
โข Function
โ Coenzymes in redox reactions (TCA, FA synthesis, gluconeogenesis, etc.)
โ DNA repair
โข Sources
โ Unrefined grains, fortified cereal, meat, fish, tomatoes, mushrooms, milk,
liver, rice
โ Metabolism of tryptophan when AA is abundant (needs riboflavin and B6)
โข RDA
โ 14-16 NE/day (NE = niacin equivalents = 1 mg niacin or 60 mg
tryptophan)
โข Deficiency
โ Pellagra = โrough skinโ
โข Toxicity
โ Skin inflammation, heartburn, nausea, liver damage
7. Pyridoxine B6
โข Vitamin B6, pyridoxal, pyridoxamine
โข Biologically active form
โ pyridoxal phosphate (PLP)
โข Function
โ Coenzyme for transamination reactions, esp. AAs (neurotransmitters)
โ Decarboxylation of carboxylic acids
โข Sources
โ Wheat, corn, egg yolk, liver, potato, banana, fish, chickpeas
โข RDA
โ 1.3-1.7 mg
โข Deficiency
โ Induced by TB drug isoniazid (supplement given)
โ Dermatitis, fatigue
โ Depression, confusion
โ Convulsions, seizures
โ Microcytic hypochromic anemia
โ Epidemic in 1950s
โข Toxicity
โ Neurological disorders at > 2 g /day
8. Biotin B7
โข Biologically active form
โ Binds to lysine residue of enzyme
โข Function
โ Cofactor in carboxylation reactions, carrier of CO2 (acetyl-CoA to
malonyl-CoA, synthesis of fatty acids)
โ Regulation of gene expression
โข Sources
โ Almost all food, esp. milk, egg yolk, tomato, almond, peanuts, avocado,
mushroom
โ Also synthesized by intestinal bacteria
โข RDA
โ At least 30 mg/day
โข Deficiency
โ Deficiency does not occur naturally unless eat 20 raw egg whites per day
(protein avidin binds biotin irreversibly and excreted)
9. Folic acid
โข Biologically active form
โ Tetrahydrofolate (THF)
โข Function
โ Stimulates digestive acids; appetite
โ Receive one carbon fragments from donors and transfer them in AA synthesis
and nucleotide synthesis
โข Sources
โ Green leafy veggies (โfoliageโ), organ meats, legumes, okra, whole grain cereals
โข RDA
โ 400 mg/day, more during pregnancy and lactation
โข Deficiency
โ Megaloblastic /macrocytic anemia and growth failure
โ Once, most common vitamin deficiency in US; now fortified cereals
โ Absorption inhibited by many medicines, so a problem with the elderly
10. Cobalamin 12
โข Vitamin B12
โ 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)
โข Function
โ Synthesis of Met
โ Methylmalonyl-CoA to succinyl-CoA
โข Degradation of odd-chain FA, enter TCA
โ Transfer of methyl groups
โ Produce red blood cells
โข Sources
โ Liver, whole milk, cottage cheese, oysters, salmon, clams, eggs, shrimp, pork,
chicken (animal sources)
โข RDA
โ 2.4 mg/day
โข Deficiency
โ Caused by pernicious anemia
โ Methylmalonic acidemia (MMA)