water soluble vitamins - vitamin B complex

what are the members of the vitamin B complex?

1. thiamin (B1)

2. riboflavin (B2)

3. niacin (B3)

4. pyridoxine (B6)

5. biotin (B7)

6. folic acid (B9)

7. cyanocobalamin (B12)

8. pantothenic acid (B5)

B4, B8, B10 and B11 do not fit the criteria for vitamin status and thus are not considered a part of the vitamin B complex

chemistry of thiamin

• heat labile sulfur containing vitamin

• contains a pyrimidine ring and thiazole ring which are joined by a methylene bridge

• highly alkaline sensitive

absorption and transportation of thiamin

absorbed in small intestine by active transport mechanism and simple diffusion, then it reaches the liver through circulation

function of thiamin

• thiamin pyrophosphate (TPP or TDP) is the active form of thiamin

• formed from thiamin in the presence of ATP in a reaction catalyzed by thiamin kinase present in the liver

• TPP is the prosthetic group of enzymes like:

  • pyruvate dehydrogenase

  • α-keto glutarate dehydrogenase, etc.

what are some sources of thiamin?

rich sources:

• outer coatings of food grains like rice, wheat and yeast

good sources

• whole cereals, pulses, oilseeds and nuts

fair sources

• meat, liver, egg and fish

what are some things thiamin deficiency can cause?

• adult beriberi, which is further spilt into

  • wet and dry beriberi

• infantile beriberi

what are early signs of adult beriberi?

• insomnia

• headaches

• dizziness

• loss of appetite

• muscle weakness

• numbness

• prickling sensation in lower limbs

• fatigue

what can adult beriberi lead to if not treated?

1. wet beriberi

2. dry beriberi

what is wet beriberi?

• in which the cardiovascular system is affected and it is characterized by edema

• edema appears in the lower limbs, trunk, face and serous cavities. blood pressure becomes abnormal, and the heart becomes weak, which can lead to death through heart failure

what is dry beriberi?

• in which the central nervous system is affected

• in addition to early signs of adult beriberi, severe muscle wasting occurs

• as a result, the individual is unable to walk and becomes bed ridden. death may occur if left untreated

what is infantile beriberi?

in infants, thiamin deficiency causes infantile beriberi. it occurs in infants between 2-10 months of age

chemistry of riboflavin

• contains a heterocyclic isoalloxazine ring and a ribitol (a sugar alcohol)

• sensitive to ligh and alkali, but stable to heat and acidic mediums

what can a riboflavin deficiency cause?

in humans, riboflavin deficiency can cause oral, facial, and ocular lesions

what oral lesions are caused by riboflavin deficiency?

• angular stomatitis, which are lesions of the mouth, particularly at the corners of the mouth

• glossitis, which is an inflamed, magenta colored tongue

what facial lesions are caused by riboflavin deficiency?

cheilosis, which is red, swollen and cracked lips

what ocular lesions are caused by riboflavin deficiency?

vascularization of the cornea and conjunctiva and bloodshot eyes

chemistry of niacin

• the word niacin refers to two pyridine derivatives, which are:

  1. nicotinic acid

  2. nicotinamide

• both are highly stable to heat and stable to alkali and acid

absorption and transportation of niacin

nicotinic acid and nicotinamide are absorbed in the small intestine and reach various tissues through circulation, which they are then converted into NAD and NADP

functions of niacin

• nicotinamide is a component of two enzymes, NAD and NADP.

• NAD is nicotinamide adenine dinucleotide

• NADP is nicotinamide adenine dinucleotide phosphate

sources of niacin

• whole grains, peanuts, legumes, yeast, liver, fish and met are good sources

• milk and egg are poor sources but a rich source of tryptophan

• vegetables and fruits are also a poor source

what can a niacin deficiency cause?

• it can cause pellagra, in which skin, gastrointestinal tract and nervous system are affected

• dermatitis, diarrhea and dementia are characteristic symptoms of pellagra

chemistry of pyridoxine

• three compounds derived from pyridine that show vitamin B6 activity. they are:

  1. pyridoxine

  2. pyridoxal

  3. pyridoxamine

• it is stable to heat and sensitive to light and alkali

absorption and transportation of pyridoxine

• easily absorbed and reaches various tissues through circulation

• in the tissues, pyridoxine is converted into pyridoxal and pyridoxamine

functions of pyridoxine

• pyridoxal phosphate is the active form. it is formed when pyridoxal by phosphorylation is catalyzed by pyridoxal kinase

• pyridoxal phosphate acts as a prosthetic group / coenzyme of enzymes, which are involved in transamination, decarboxylation, transsulfuration, desulfuration and non-oxidative deamination occurs

• pyridoxal phosphate is also a coenzyme for enzymes that are involved in the synthesis of heme, serotonin, catecholamines and coenzyme A synthesis

sources of pyridoxine

• whole grains, legumes, liver and yeast are good sources

• leafy vegetables, milk, meat and eggs are fair sources

pyridoxine deficiency

1. rare in human adults

2. in children, it causes epileptic form of convulsions (seizures) due to decreased formation of neurotransmitters like GABA, serotonin and catecholamines

chemistry of biotin

• sulfur containing vitamin

• consists of imidazole ring that is fused to a tetrahydro thiophene with a valerie acid side chain

• stable to heat, but alkaline sensitive

absorption and transportation of biotin

• absorbed in the small intestine and reach the liver and other tissues through circulation

function of biotin

• prosthetic group of several carboxylases like pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase, etc

• attached to e-amino groups of lysyl residue of apoenzyme through amide linkage

• in carboxylation reactions, it acts as a carrier of CO2

dietary sources of biotin

• whole cereals, legumes, groundnuts, milk, meat and fish are good sources

• vegetables and fruits are fair sources

biotin deficiency

rare in humans because it is present in most common foods