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All You Need to Know About the Mysterious Vitamin- B Complex

The author is a Med-Student who is passionate about writing informative articles that adds value to the reader's life.



Vitamins play a crucial role in maintaining our health and welfare, and their deficiencies can lead to a variety of symptoms which are an alert signal indicating supplementation. Unlike other vitamins, Vitamin B is a complex vitamin and it is sub-divided into B1, B2, B3, B5, B6, B7, B9 and B12. It is Water soluble and hence readily excreted through urine. This article explains in detail all that you need to know about this mysterious vitamin.


  • Thiamine also known as anti-beriberi, works by taking the form of a coenzyme ‘THIAMINE PYROPHOSPHATE’[TPP].
  • This coenzyme TPP is mostly associated with enzymes of carbohydrate metabolism and enzymes involved in branched chain amino acids metabolism such as a] pyruvate dehyrdrogenase b] alpha ketoglutarate dehydrogenase and c]alpha keto acid dehydrogenase.These enzymes are involved in energy releasing mechanisms.
  • HMP shunt enzyme ‘ transketolase’ also requires TPP.
  • TPP also plays an important role in transmission of nerve impulses.
  • Dietary sources include cereals, pulses, oil seeds and animal food such as pork, liver etc. Polishing of rice removes 80% of thiamine.
  • Since it is a water-soluble vitamin, it is extracted into the water during cooking process, hence such water should not be discarded.
  • DEFICIENCY causes beriberi (especially seen in population consuming exclusively polished rice). Symptoms include loss of appetite, weakness, constipation, and nausea. Neurological symptoms include Wernicke’s encephalopathy and Korsakoff syndrome.
  • RDA for adults is 1-1.5 mg [ depends upon carbohydrate intake]


  • Riboflavin through it’s co-enzymes takes part in a variety of cellular oxidation-reduction reactions, which are responsible for energy production.
  • It has 2 co-enzyme forms, which are FMN [ Flavin mononucleotide] and FAD [ Flavin adenine dinucleotide].
  • These co-enzymes serve as an acceptor of 2 hydrogen atoms forming FMNH2 and FADH2 respectively, and they are associated with certain enzymes involved in Carbohydrate, Lipid, Protein and Purine metabolisms besides the Electron Transport Chain.
  • Dietary sources includes milk and meat.
  • DEFICIENCY symptoms are a] Cheilosis - fissures at the corners of the mouth, b] Glossitis- tongue smooth and magenta coloured c] Dermatitis [ seborrhagic dermatitis]
  • RDA is 1.2-1.7 mg for adults.


  • The co-enzymes of niacin (NAD+ and NADP+) can also be synthesized by the essential amino acid tryptophan.
  • 60 mg of tryptophan is equivalent to 1 mg of niacin for niacin co-enzymes synthesis.
  • The co-enzymes participate in several oxidation- reduction reactions as they exist in both oxidized (NAD+/NADP+) and reduced (NADH2/NADPH2) forms.
  • NADH plays a crucial role in ATP generation, whereas NADPH2 are important for biochemical reactions as they donate reducing equivalents.
  • Niacin causes lowering of circulating lipid levels like LDL, VLDL and increases HDL. It is used in treatment of hyperlipidemic conditions. However, Niacin leads to insulin resistance and consequently causes hyperglycemia. Therefore, patients with DM on Niacin should monitor glucose levels frequently.
  • Dietary sources include liver, yeast, whole grains, cereals, pulses and peanuts.
  • RDA is 15-20 mg for adults
  • Deficiency causes pellagra meaning ‘rough skin’ -[ seen in patients consuming food rich in Leucine, as it inhibits tryptophan which is required for Niacin synthesis]
  • It is characterized by the 4 D’s

a) Dermatitis- esp areas exposed to sunlight

b) Diarrhoea

c) Dementia

d) Death



  • Pantothenic acid is one of the most widely distributed vitamins found in plants and animals.
  • Its role as COENZYME -A is also widespread. The synthesis of coenzyme-A from pantothenic acid occurs in a series of reactions.
  • Functions of coenzyme A are,

A] It is a central molecule involved in all the metabolisms such as carbohydrate, protein and lipid. Hence, it is known as Coenzyme of metabolic integration.

B] When bound to acetyl unit, it forms acetyl CoA and with succinate it forms succinyl CoA. There are many other compounds bound to coenzyme A

C] It is a carrier of activated acetyl or acyl groups.

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  • Pantothenic acid itself helps in fatty acid synthesis as it a component of ‘fatty acid synthase complex’.
  • Dietary source- It is a widely distributed vitamin found in plants and animals. The richest sources are egg, liver, meat, yeast, milk, etc.
  • RDA is 5-10 mg for adults
  • DEFICIENCY causes burning feet syndrome- pain and numbness in toes, sleeplessness and fatigue.


  • Vitamin B6 collectively represents the three compounds pyridine [primary alcohol], pyridoxal [ aldehyde form] and pyridoxamine [amine].
  • The active form is the coenzyme pyridoxal phosphate [PLP]. It is closely associated with metabolism of amino acids, as it participates in reactions such as :

A] Transamination- Converting amino acids to ketoacids Eg) Alanine to pyruvate, Aspartate to oxaloacetate requires TPP.

B] Decarboxylation- In reactions involving synthesis of 5HT, GABA, Histamine, Dopamine and NE from Tryptophan, Glutamate, Histidine and Tyrosine respectively.

C] Transsulfuration- Transfer of sulphur group in sunthesis of Cysteine from Homocysteine

D] PLP is requires for HEME synthesis etc.

  • Vitamin B6 is excreted in urine as 4-pyridoxic acid. In B6 deficiency, increased urinary excretion of Xanthurenic acid serves as a reliable index.
  • Dietary sources: Animal source- egg yolk, fish, milk, meat Plant source- Wheat, corn, cabbage, roots and tubers.


A] NEUROLOGICAL SYMPTOMS- depression, irritability, mental confusion and nervousness. Severe deficiency causes convulsions and peripheral neuropathy. This is attributed to reduced GABA, serotonin and NE functions

B] REDUCED HEME PRODUCTION- causes Iron deficiency anemia related symptoms.

  • RDA is 1.5-2 mg for adults
  • Antidote: Isoniazid, deoxypyridoxine


  • It is also known asanti-egg white injury factor ‘ and ‘ Vitamin H’.
  • It can also be synthesized by intestinal bacteria.
  • Consumption of raw eggs lead to biotin deficiency, due to the presence of ‘egg white injury factor’ aka ‘Avidin’ which inhibits biotin absorption. However, cooked eggs do not produce these symptoms.
  • Biotin directly participates as coenzyme is Carboxylation reactions.
  • Examples of carboxylation reactions where biotin is required are: A] Conversion of pyruvate to oxaloacetate by biotin dependent pyruvate carboxylase. B] Conversion of Acetyl CoA to Malonyl CoA in fatty acid synthesis by Acetyl CoA carboxylase. Etc
  • Dietary sources include both plants and animals. Richest sources are Liver, Kidney, egg yolk etc.
  • RDA is 20-30 micrograms for adults.
  • Deficiency: Symptoms include anemia, loss of appetite, nausea, alopecia. It is seen is conditions such as prolonged antibiotic use and prolonged raw egg consumption.
  • Antidote: Desthiobiotin and biotin sulphonic acid.


  • Folic acid / folacin is abundantly found in green leafy vegetables.
  • The active form of folic acid is tetrahydrofolate (THF).
  • This coenzyme is involved in one carbon metabolism, as it serves as an acceptor or donor of one carbon units such as formyl, methyl, etc .
  • Synthesis of important compounds such as purines, pyrimidines, glycine, etc occur by this one ‘C’ metabolism.
  • RDA is 200 micrograms for adult.
  • Dietary sources: Green leafy vegetables are the richest source.
  • Deficiency: [It is the most common vitamin deficiency, seen primarily in pregnant women] a) Macrocytic anemia- due to impaired DNA synthesis which leads to reduced RBC maturation. b) Neural defects in fetus.


  • It is a unique vitamin synthesized by only microorganisms and not by animals and plants.
  • The structure of vitamin B12 has a Corrin ring with a central cobalt atom.
  • Depending on the substituent attached to cobalt atom, vitamin B12 has the following subtypes: a) Cyanide in Cyanocobalamin [B12a] b] Hydroxyl in Hydroxycobalamin [B12b] c] Nitrite in Nitrocobalamin [B12c]
  • Absorption of vitamin B12 occurs in distal ileum and requires Castle’s intrinsic factor.
  • Uses: 2 reactions in mammals are dependent on Vitamin- B12
  • A) Synthesis of methionine from homocysteine , here the coenzyme form is Methylcobalamin
  • B) Isomerization of Methylmalonyl CoA to Succinyl CoA, here the coenzyme form is Deoxyadenosyl Cobalamin .
  • RDA is 1-2 microgram for adults
  • Dietary sources: Food of animal sources are the only sources of vitamin B12, as it is synthesized by gut microbacteria.
  • Deficiency: causes pernicious anemia- due to reduced hemoglobin production. Neurological symptoms due to accumulation of methyl malonyl coA.

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