Vitamins and Vitamin A Overview

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)

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)

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

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

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.

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

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

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)

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)

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.

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

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