Vitamins: Roles, Sources, Requirements and Deficiencies

Vitamins: Roles, Sources, Requirements and Deficiencies

1. Overview

• Vitamins are organic compounds that are essential for the body in small amounts but cannot be synthesized by the body.

• We must obtain vitamins from our diet.

• Vitamins are classified into two groups: water-soluble vitamins and fat-soluble vitamins.

2. Water-soluble vitamins

• Roles: Involved in the formation and function of many enzymes, acting as coenzymes.

• Transport: Freely transported in the blood.

• Handling excess: Easily excreted in the urine.

• Water-soluble vitamins: Vitamin B (B1, B2, B3, B5, B6, B9, B12), Vitamin C.

3. Fat-soluble vitamins

• Roles:

• Antioxidant.

• Precursors of hormone-like substances.

• Transport: Transported in the form of lipoproteins or attached to specific proteins.

• Handling excess: Must be converted to a water-soluble form before excretion through the kidneys.

• Fat-soluble vitamins: Vitamin A, D, E, K.

4. Holoenzyme

• Formation: An enzyme combines with a coenzyme.

5. Vitamin B1 (Thiamin)

• Other names: Thiamin.

• Active form: Thiamin pyrophosphate.

• Requirement:

• Adults: 1mg/day.

• Children: 0.4-1.3 mg/day.

• Source:

• Abundant: Brewer’s yeast, rice bran.

• Less abundant: Pork, liver, egg yolk.

• Properties: White crystalline powder, yeast-like aroma, slightly bitter taste, soluble in water, insoluble in ether, degraded by heat.

• Function: Involved in carbohydrate metabolism, easily absorbed through the digestive tract.

• Deficiency: Beriberi.

• Causes of deficiency: Alcoholism, malnutrition, long-term dextrose infusion.

• Symptoms of deficiency: Loss of appetite, cramps, irritability.

6. Vitamin B2 (Riboflavin)

• Other names: Riboflavin.

• Active form: FMN, FAD.

• Function:

• Flavin coenzyme: Important electron carrier in redox reactions in the cellular respiratory chain.

• Oxidation of AB and aa, CTAC.

• Source: Bran, milk, brewer’s yeast, meat, egg white, leafy vegetables, fruits…

• Absorption: Mainly absorbed through the intestine.

• Handling excess: Excreted in urine, feces.

• Role: A coenzyme for about 20 enzymes (e.g. glycin oxidase).

• Requirement:

• Adults: 1.5-2.5 mg/day.

• Children: 1-1.8 mg/day.

• Symptoms of deficiency: Digestive disorders, corneal inflammation, glossitis, lip ulcers, seborrheic dermatitis, anemia.

7. Vitamin B3 (Niacin, Vitamin PP)

• Other names: Niacin, Vitamin PP.

• Source: Liver, meat, fish, beans.

• Structure: Nicotinic acid and nicotinamide.

• Role:

• The active form is NAD, NADP: catalyzes redox reactions in cellular respiration -> ATP.

• Carbohydrate metabolism, protein metabolism, fat formation.

• Causes of deficiency: Alcoholism, malnutrition in children, drug interactions, eating corn instead of rice.

• Symptoms of deficiency:

• Mild: Loss of appetite, weakness, glossitis.

• Severe: Pellagra: Dermatitis, diarrhea, dementia.

8. Vitamin B5 (Pantothenic)

• Other names: Pantothenic.

• Source: Egg yolk, kidney, liver.

• Absorption: Absorbed through the digestive tract.

• Handling excess: Excreted in urine (70%).

• Role: A vital component of coenzyme A, involved in acetyl group metabolism (carbohydrate oxidation, glucose neogenesis, AB degradation, steroid hormone synthesis).

• Structure: Alanine linked to pantoic acid.

• Causes of deficiency: Adrenal insufficiency.

• Symptoms of deficiency: Muscle cramps, fatigue, headache, sleep disturbances, nausea, vomiting, abdominal pain, dyspepsia, enteritis, diarrhea, hair loss.

9. Vitamin B6 (Pyridoxine)

• Other names: Pyridoxine.

• Source: Meat, liver, kidney, brewer’s yeast, wheat germ.

• Active form: Pyridoxal.

• Role: A coenzyme that plays a role in amino acid metabolism.

• Forms: Pyridoxine, pyridoxal, pyridoxamine.

10. Vitamin B9 (Folic acid)

• Other names: Folic acid.

• Source: Fruits and leafy vegetables, animal liver, mushrooms, brewer’s yeast.

• Role: Essential for cell growth and reproduction, acts on bone marrow, involved in blood formation.

• Requirement: 100 micrograms/day.

• Structure: Pteroyl combined with glutamic acid.

• Causes of deficiency: Reduced absorption, lack of dietary sources, patients with liver disease and alcoholism, vitamin B12 deficiency.

• Symptoms of deficiency: Megaloblastic anemia, pallor, rapid heartbeat, enlarged liver and spleen, stomatitis, glossitis, diarrhea.

11. Vitamin B12 (Cyanocobalamin)

• Other names: Cyanocobalamin.

• Source: Found only in animals (liver, kidney, milk, eggs), streptomyces griseus bacteria.

• Role: A coenzyme involved in 1-carbon transfer reactions (such as folic acid): methylcobalamin, 5-deoxydiadenosyl-cobalamin.

• Structure: Cobalamin.

• Requirement: 3 mg/day.

• Causes of deficiency: Lack of dietary sources, inadequate secretion of intrinsic factor by the stomach, congenital deficiency of transcobalamin II.

• Symptoms of deficiency: Megaloblastic anemia, loss of balance, memory loss, dementia.

12. Vitamin C (Ascorbic acid)

• Other names: Ascorbic acid.

• Source: Vegetables, sour green fruits.

• Role:

• A powerful antioxidant.

• Involved in metabolism:

• Protein: Metabolism of phenylalanine, tyrosine.

• Lipid: Synthesis of adrenal steroid.

• Carbohydrate: Regulation of aconitase enzyme.

• Requirement: 6 mg/day.

• Other functions: Converts Fe3+ -> Fe2+ (absorption through the gut), converts folic acid -> folinic acid, methemoglobin -> hemoglobin.

• Causes of deficiency: Lack of dietary sources, elderly, alcoholics, infants 6-12 months, urban poor.

• Symptoms of deficiency: Subcutaneous bleeding, joint bleeding causing pain, bleeding gums, swollen gums, anemia.

13. Vitamin A (Retinol)

• Other names: Retinol.

• Source:

• Animals: Cod liver oil, butter, milk, egg yolk.

• Plants: Provitamin A is beta-carotene (carrots, pumpkins, gac, tomatoes).

• Absorption: Through the intestinal membrane with the help of bile salts.

• Forms in the body: Stored in the liver 90%, then into the blood combined with a protein retinol binding protein.

• Structure: Two retinal molecules linked together by the enzyme beta-carotene dioxygenase.

• Role: Vision (maintaining the sensitivity of the eyes to light reception), maintaining epithelial integrity, playing a role in cell growth and proliferation (necessary for development, especially in embryos, children and adolescents), beta-carotene slows down the rate of accelerated degeneration.

• Causes of deficiency: Poor fat absorption (intestinal, pancreatic disease, alcoholism), deficiency due to supply.

• Symptoms of deficiency:

• Mild: Night blindness, xerophthalmia.

• Severe: Corneal ulcers and necrosis, keratitis, blindness.

• Requirement: 5000 IU/day (higher for children, pregnant women).

14. Vitamin D (Calciferol)

• Other names: Calciferol.

• Source:

• Provitamin D3 is 7-dehydrocholesterol found in the skin -> cholecalciferol (D3).

• D3 is found in cod liver oil, animal fat, butter, milk, egg yolk.

• Provitamin D2 is ergosterol found in fungi, brewer’s yeast -> ergocalciferol (D2).

• Transport to the liver: 25-hydroxycholecalciferol (25-OH-D3).

• Transport to the kidneys: 1,25-dihydroxycholecalciferol (1,25-DiOH-D3).

• Activity in tissues: More potent.

• Role: Increases Ca absorption in the gut, increases Ca mobilization from bone to blood, increases Ca and phosphate absorption in the proximal tubule, cartilage growth necessary for bone development in children.

• Causes of deficiency: Lack of sunlight exposure, liver, intestinal, kidney diseases, increased requirement during pregnancy, breastfeeding, use of anticonvulsants, lack of dietary sources.

• Requirement: 400 IU/day.

• Symptoms of deficiency: Decreased blood Ca, children with rickets (soft bones, deformities), osteomalacia in adults.

• Symptoms of excess: Toxicity due to Ca accumulation in blood and kidneys.

15. Vitamin E (Tocopherol)

• Other names: Tocopherol.

• Source: Vegetable oils, beef liver, egg yolk, green vegetables.

• Features: Heat-stable (withstands 100*C when boiled with concentrated HCl).

• Types: Alpha, beta, gamma – tocopherol.

16. Vitamin K

• Causes of deficiency: Excessive antibiotic use, lack of bile for absorption, use of anticoagulants (heparin, salicylates, phenylbutazone).

• Symptoms of deficiency: Prolonged prothrombin time.