Vitamins: Functions, Sources, Deficiencies, and Toxicity

Posted on Dec 16, 2024 in Biology

Vitamin A

Vitamin A is a group of compounds organized into two classes:

  • Retinoids: Preformed vitamin A found in food of animal origin, such as meat, eggs, and dairy products.
  • Carotenoids: Precursors of vitamin A present in plant foods (fruits and vegetables), like beta-carotene from green leaves.

Features

  • Cell differentiation
  • Reproduction
  • Growth
  • Development of bones and teeth
  • Synthesis and maintenance of a healthy epithelium (like the retina)
  • Immune system integrity
  • Prevention of night blindness (an essential component of rhodopsin, a light-sensitive pigment)

Metabolism

Preformed vitamin A is more bioavailable and better absorbed than carotenoids.

  • Stored mainly in the liver.
  • Transported in the blood by retinol-binding protein (RBP) and prealbumin.

Deficiency

  • Limited access to food.
  • Low consumption of vitamin A or carotene.
  • Low-fat diet.
  • Keratinization: dry skin.
  • Xerophthalmia: dry eye. It is the early stage of night blindness, followed by xerosis (dryness and corneal opacity).

Toxicity = Hypervitaminosis

  • Can be acute or chronic.
  • Caused by over-supplementation with preformed vitamin A.
  • Not associated with high doses of beta-carotene.
  • Excess carotene can cause orange coloring on the hands and mouth.

B Vitamins

B1 Thiamine

(First discovered in the B complex)

  • Essential for DNA formation and synthesis of acetylcholine (a neurotransmitter).
  • Active form: thiamine pyrophosphate (TPP), a component of coenzymes.
  • Transforms carbohydrates and proteins into energy.
  • Found mostly in muscle and liver.
  • Excreted in urine (half-life of 9 to 19 days).
  • Sources: fortified cereals and breads, fish, lean meat, and milk.
  • Deficiency: common in alcoholics and people with cardiovascular or neurological problems, affecting metabolism.
  • Toxicity: renally eliminated (no known problems).

B2 Riboflavin

  • Heat-stable.
  • Fluorescent pigment.
  • Functions: part of enzymes, helps release energy in metabolic pathways of carbohydrates, promotes healthy growth.
  • Metabolism: absorbed by active transport, excreted in urine.
  • Sources: cereals, nuts, milk, eggs, leafy greens, lean meats.
  • Deficiency: glossitis (inflammation of the tongue), cheilosis (cracks in the corners of the mouth), angular stomatitis (mouth inflammation).
  • Toxicity: no known problems.

B3 Niacin

Two active forms: nicotinamide and nicotinic acid.

  • Stable to heat, acid, light, and oxygen.
  • Functions: forms enzymes in the electron transport chain, involved in metabolic pathways of carbohydrates, steroids, and red blood cells.
  • Metabolism: almost completely absorbed. Levels measured by metabolites excreted in urine.
  • Sources: dairy products, poultry, fish, lean meats, nuts, and eggs.
  • Deficiency: pellagra, which causes dementia, diarrhea, and dermatitis (the 3 Ds).
  • Toxicity: decreases LDL and increases HDL; only an issue with supplements.

B6 Pyridoxine

  • Composed of pyridoxine (plants, more stable) and pyridoxal (animals). Both are destroyed by light or neutral and alkaline media.
  • Functions: involved in amino acid metabolism, synthesizes and develops red blood cells, converts tryptophan to niacin.
  • Metabolism: passive absorption, stored in liver and muscle, excreted in urine.
  • Sources: beans, nuts, eggs, cereals, bread, fish, meats, vegetables.
  • Deficiency: seizures, depression, secondary pellagra, microcytic anemia.
  • Toxicity: often used in therapies for neurological syndromes, menstrual issues, and carpal tunnel.

B9 Folic Acid or Folate

Discovered as an antianemic factor for pregnant women.

  • Folate: natural form.
  • Folic acid: more bioavailable synthetic form.
  • Functions: synthesis of coenzymes, metabolism of amino acids, regeneration of enzymes, DNA synthesis, and cell division.
  • Metabolism: actively and passively absorbed, binds to proteins in the blood for transport, mainly stored in the liver, excreted in bile.
  • Sources: beans, legumes, citrus fruits, whole grains, poultry, pork, seafood, and liver.
  • Deficiency: anemia, birth defects (anencephaly, spina bifida).
  • Toxicity: may increase colorectal cancer risk.

B12 Cobalamin

One of the more complex vitamins.

  • Synthetic form: cyanocobalamin.
  • Red color (cobalt ore).
  • Sources: foods of animal origin (eggs, seafood, milk, and derivatives).
  • Destroyed in the presence of heavy metals, oxidizers, and reducers.
  • Functions: essential for coenzymes, DNA formation, maturation of red blood cells, amino acid activation, synthesis of nucleoproteins and neurotransmitters.
  • Metabolism: binds to intrinsic factor in the stomach’s acidic environment, absorbed in the ileum, stored in the liver. Measured by complete blood count (CBC).
  • Deficiency: anemia, confusion, impaired neurological function, and impaired erythropoiesis.
  • Toxicity: no comment.

Vitamin C

  • Structure similar to glucose.
  • Humans cannot synthesize it.
  • Destroyed by light, heat, alkaline media, copper or iron minerals, and oxygen.

Features

  • Electron donor for enzymes.
  • Forms collagen, serotonin, and norepinephrine.
  • Protects vitamin A and polyunsaturated fatty acids from oxidation.
  • Prevents aging.
  • Facilitates the absorption of calcium and iron.
  • Involved in carcinogenic processes.
  • Participates in the synthesis of leukocytes.

Metabolism

90% is reabsorbed.

Increased Intake Recommended For

  • Smokers.
  • Those with infections such as pneumonia and tuberculosis.
  • Those with high collagen demands (burns, fractures).

Sources

Citrus fruits, green peppers, strawberries, tomatoes, broccoli, white potatoes.

Deficiency

Scurvy, anemia, bruising, weakness, bleeding gums.

Toxicity

Kidney stones, nausea, vomiting, diarrhea, increased uric acid excretion.

Vitamin D

  • Group of sterol compounds (steroids).
  • Precursors activated by exposure to sunlight.
  • Can be synthesized in the body (when exposed to sunlight) or consumed as a supplement (butter, cheese, margarine, cereals, fish).

Features

  • Aids intestinal absorption of calcium and phosphorus for bones and teeth.
  • Helps regulate plasma levels of calcium and phosphorus.
  • Supports skeletal muscle, heart, and nervous system function.
  • Affects cellular activity of the skin, pancreas, ovaries, and other organs.
  • May decrease the risk of breast cancer in pre-menopausal women.

Factors That Interfere With Requirements

  • Periods of rapid growth.
  • Older adults.
  • Liver and kidney disorders.
  • Dark skin (less vitamin D production).
  • Drug use.
  • Latitudes above 42ยบ.

Deficiency

  • Low plasma calcium levels.
  • Reduced tooth enamel calcification.
  • Alteration in bone mineralization.
  • Rickets in children (thinning and softening of the bones due to extreme lack of calcium).
  • Osteomalacia in adults.

Toxicity

  • High toxicity.
  • Excessive increase in intestinal calcium absorption and bone resorption (hypercalcemia and calcium deposition in organs).
  • Altered dental training and calcification (hypoplasia).
  • May cause hypervitaminosis.
  • Symptoms: loss of appetite, polydipsia, vomiting, diarrhea, fatigue, decreased bone density.
  • Hypercalcemia, kidney damage, and heart damage.

Vitamin E

  • Compounds with the metabolic activity of alpha-tocopherol.
  • Found in corn, nuts, olives, greens, wheat germ, and vegetable oils.

Features

  • Potent antioxidant.
  • Protects against lipid oxidation in cell membranes.
  • Prevents white blood cell hemolysis.
  • Aids in red blood cell formation.
  • Protects vitamin A from oxidation.
  • Prevents cataracts with carotenoids.
  • Inactivates free radicals.
  • Prevents the carcinogenic effect of nitrosamines.
  • Stimulates the immune response.
  • Prevents LDL oxidation (plasma lipoproteins).

Metabolism

  • Absorbed with dietary fat.
  • Alpha-tocopherol is absorbed 20 to 80%.
  • Stored in most organs (especially liver and adipose tissue).
  • Transported by lipoproteins.
  • Excreted in bile and possibly urine and skin.

Requirements

DRI:

  • Children older than 13 years: 6-11 mg/day
  • Men and women: 15 mg/day

UL:

  • Children: 200-800 mg/day
  • Adults: 1000 mg/day

Deficiency

Rare. More common in premature infants.

Toxicity

3 g per day can cause bleeding gums.

Vitamin K

  • Plants: phylloquinone (K1)
  • Gastrointestinal tract: menaquinone (K2) secreted by bacteria.
  • Synthetic and water-soluble: menadione (K3)

Features

  • Fundamental in the process of coagulation in the liver.
  • Activates proteins involved in bone formation.

Metabolism

  • Stored in the liver and excreted in bile and urine.
  • Metabolized along the intestine (by bacteria).
  • Levels measured by blood clotting tests.

Deficiency

Common in newborns, people with liver disease, those with intestinal flora disturbed by antibiotics, and vitamin K antagonists.

Toxicity

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