Vitamins and Vitamin A Overview

Vitamins

• Vitamins are essential for normal metabolism
• Humans cannot synthesize some vitamins (except vitamin D)
• Vitamin deficiency can be primary (inadequate intake) or secondary (absorption or increased metabolism issues)
• Vitamins are classified as water-soluble (B vitamins and vitamin C) and fat-soluble (vitamins A, D, E, and K)

Vitamin A

• A generic term for retinol and related substances (retinoids)
• Fat-soluble vitamin, requiring bile for absorption and stored in the liver
• Principal actions:
  • Maintaining normal epithelial tissue
  • Promoting cornea and conjunctiva development
  • Enhancing immune function
  • Forming retinal photochemical
• Sources: Liver, dairy products, green vegetables, yellow fruits
• Deficiency symptoms: Xerophthalmia, photophobia, bitot spots, conjunctivitis, blindness, squamous cell metaplasia, hyperkeratosis, impaired immune function
• Excess symptoms: Anorexia, skin dryness/cracking, long bone swelling/pain, increased intracranial pressure, alopecia
• Therapeutic uses: Treating chronic plaque psoriasis (tazoreotene), acne (tretinoin), acute promyelocytic leukemia (tretinoin)

Vitamin B1 (Thiamine)

• Water-soluble vitamin
• Component of thiamine pyrophosphate, involved in alpha-keto acid decarboxylation and citric acid cycle
• Thiamine pyrophosphate is a cofactor for glutamic acid and GABA production (neurotransmitters)
• Sources: Meat, whole grains, legumes, nuts
• Deficiency symptoms: Wernicke encephalopathy (ophthalmoplegia, ataxia, confusion), Korsakoff syndrome (amnesia, memory deficit, confabulation), beri-beri.
• Deficiency usually due to poor intake or chronic alcoholism

Vitamin B2

• Member of flavoprotein enzymes, important in oxidation-reduction reactions
• Water-soluble vitamin
• Sources: Milk, cheese, meat, vegetables, eggs
• Deficiency (Ariboflavinosis): Angular stomatitis, glossitis, photophobia, blurred vision, burning and itching eyes, poor growth

Vitamin B3 (Niacin)

• Converted to nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADPH) — essential for tissue respiration.
• Sources: Meat, fish, poultry
• Deficiency (pellagra): Dermatitis, diarrhea, dementia
• Deficiency linked to reduced tryptophan intake, alcoholism, carcinoid syndrome, Hartnup disease, and chronic inflammatory bowel syndrome.

Vitamin B6 (Pyridoxine)

• Co-enzyme in amino acid metabolism (decarboxylation and transamination)
• Sources: Meat, fish, fortified cereals
• Deficiency symptoms: Microcytic anemia, dermatitis, cheilosis, impaired immune function.
• Medical use: Treating pyridoxine-dependent inborn errors of metabolism (e.g., homocystinuria, hereditary sideroblastic anemia, primary hyperoxaluria)
• Drug-induced deficiency: Isoniazid, hydralazine, penicillin

Vitamin B12

• Cobalamin family, with cobalt within a central corin ring
• Essential for DNA synthesis, red blood cell production, methylation, and myelin synthesis
• Obtained from animal products (meat, fish)
• Absorption: Binds to intrinsic factor (IF) from gastric cells, travels to ileum for absorption, binds to transcobalamin for delivery to cells. Remaining is bound to haptocorrin and stored in the liver.
• Deficiency causes: Inadequate dietary intake (elderly, vegans), pernicious anemia (autoimmune destruction of gastric cells), malabsorption syndromes (terminal ileum issues), drugs (metformin, phenytoin), congenital defects (transcobalamin deficiency).
• Deficiency results: Megaloblastic anemia

Folic Acid

• Water-soluble B vitamin, found in green vegetables, fruits, yeast, and liver
• Absorbed in the proximal jejunum as monoglutamate
• Present in plasma as 5-methyltetrahydrofolate
• Deficiency causes: Inadequate dietary intake, malabsorption syndromes (jejunum resection, gluten-sensitive enteropathy), increased need (prematurity, pregnancy, dialysis, psoriasis), anti-folate use (anti-epileptic meds, methotrexate, trimethoprim, Pyrimethamine)
• Deficiency results: Megaloblastic anemia (due to impaired purine and pyrimidine synthesis)

Vitamin C (Ascorbic Acid)

• Powerful reducing agent (antioxidant), essential cofactor for enzymatic reactions
• Sources: Citrus fruits, strawberries, potatoes, peppers
• Deficiency (scurvy symptoms): Petechial hemorrhages, hematomas, bleeding gums, anemia
• Medical use: Treating methemoglobinemia (converting ferric iron to ferrous iron)

Vitamin D

• Structurally related sterols, crucial for calcium and phosphate absorption
• Types:
  • Vitamin D2 (ergocalciferol): Produced by UV irradiation of ergosterol in plants.
  • Vitamin D3 (cholecalciferol): Produced by UV irradiation of 7-dehydrocholesterol in the skin.
• Actions: Active transport of calcium and phosphate in the gut and renal tubules
• Deficiency symptoms: Rickets (children), osteomalacia (adults), hypocalcemia
• Sources: Sunlight exposure, fish oil, egg yolks
• Clinical use: Prevent/treat rickets, osteomalacia, osteoporosis, hypoparathyroidism, psoriasis, renal osteodystrophy.

Vitamin E

• Group of compounds (alpha-tocopherol is the most potent), fat-soluble
• Action: Antioxidant, protecting cell membranes from lipid peroxidation
• Sources: Vegetable oils, seeds, nuts, leafy greens.
• Deficiency symptoms: Red blood cell hemolysis in infants, posterior column and cerebellar dysfunction, pigmentary retinopathy

Vitamin K

• Group of naphthoquinones (K1 from diet; K2 from intestinal bacteria), fat-soluble
• Crucial for synthesis of vitamin K-dependent clotting factors (II, VII, IX, X)
• Sources: Green leafy vegetables, liver, legumes
• Deficiency symptom: Hemorrhage

Summary

• Vitamins are essential for growth and development.
• Vitamin deficiencies can range from mild to severe.
• Prompt management is key for optimal health.

Explore the essential roles of vitamins in metabolism and the classification of vitamins as water-soluble and fat-soluble. This quiz dives deep into Vitamin A, its functions, sources, deficiency symptoms, and excess symptoms. Test your knowledge on how vitamins contribute to health and well-being.