Vitamins: Types and Functions

Vitamins

• Vitamins are organic substances needed for normal cell function, growth, and development.
• They are required in microgram (µg) to milligram (mg) quantities per day, classified as micronutrients.
• Vitamins are categorized as fat-soluble or water-soluble.

Fat-Soluble Vitamins

• Fat-soluble vitamins (A, D, E, and K) dissolve in fat and accumulate in the body.
• They do not need to be consumed daily as the body stores them.

Water-Soluble Vitamins

• Water-soluble vitamins (vitamin C and the B-complex vitamins) dissolve in water before absorption; therefore, they cannot be stored.
• Any unused water-soluble vitamins are primarily lost through urine.

Vitamin A (Retinoids)

• Vitamin A exists in various forms: retinol, retinal, and retinoic acid.
• The body can convert beta-carotene and other carotenoids to retinol.
• Functions:
  • Vision
  • Reproduction
  • Growth
  • Stabilizing cellular membranes

Vitamin A Deficiency

• Rare as it can be found in animal liver.
• Deficiency may occur due to fat malabsorption.
• Deficiency can cause vision loss and blindness.
• Can also cause complications in skin, heart, lungs, tissues, and the immune system.

Vitamin A Excess (Hypervitaminosis A)

• Acute toxicity from a single massive dose leads to abdominal pain, nausea, vomiting, severe headaches, dizziness, sluggishness, and irritability, followed by skin desquamation and recovery.
• Chronic toxicity from moderately high doses is characterized by joint and bone pain, hair loss, dryness and fissures of the lips, anorexia, benign intracranial hypertension, weight loss, and hepatomegaly.

Vitamin A Excess (Carotenemia)

• Reversible yellowing of skin.
• Does not cause toxicity as its metabolic conversion is regulated by vitamin A status.

Vitamin D (Calciferols)

• Vitamin D is a group of fat-soluble vitamins from food and hormones the body produces.
• Responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and for various biological effects.

Vitamin D Functions

• Regulation of Calcium and Phosphate:
  • Increases intestinal absorption of calcium.
  • Resorption and formation of bone via parathyroid hormone (PTH).
  • Reduces renal excretion of calcium.

Vitamin D Deficiency

• Rickets in children.
• Osteomalacia in adults.

Vitamin E (Tocopherols)

• Important antioxidant, preventing oxidative damage to cell membranes.
• Stored in tissues, especially adipose tissue.

Vitamin E Deficiency

• Deficiencies in mainly three groups:
  • Fat malabsorption (e.g., cystic fibrosis).
  • Premature, very low birth weight infants.
  • Rare congenital disorders of fat metabolism (e.g., abetalipoproteinemia).
• Can result in haemolytic anemia, myopathy, retinopathy, and neuropathy.

Vitamin E Excess

• Low toxicity
• High intakes may impair absorption of other fat-soluble vitamins, resulting in vitamin K deficiency and bleeding problems.

Vitamin K

• Promotes blood clotting.
• Required for the conversion of several clotting factors and prothrombin.
• Necessary for liver synthesis of plasma clotting factors II, VII, IX, and X.

Vitamin K Sources

• Vitamin K1 (phylloquinone).
• Synthesized by plants and present in food.
• Vitamin K2 (menaquinone).
• Synthesized in humans by intestinal bacteria.
• Synthetic vitamin Ks:
  • K3 (menadione).
  • K4 (menadiol).

Vitamin K Deficiency

• Rare in adults.
• Bleeding can occur.
• Newborn infants may be deficient.
• Haemorrhagic disease of the newborn develops readily as intestinal flora have not become established within the first week of birth and early breastmilk is low in vitamin K.

Vitamin K Excess

• Vitamin K1 is relatively safe.
• Synthetic forms (especially vitamin K3) are more toxic.
• High doses can cause oxidative damage, red cell fragility, and methaemoglobin formation.
• Can cause liver and brain damage in premature infants.

Water-Soluble Vitamins

• Vitamin C
  • Adults need 40 mg/day.
  • Higher requirements in individuals with diets devoid of fresh fruits and vegetables, smokers, and those who are pregnant or recovering from surgery.
• Vitamin B complex (multiple B vitamins exist)

Vitamin C - Function

• Collagen synthesis
• Antioxidant
• Iron absorption (facilitates intestinal absorption by keeping it in the Fe²⁺ state).

Vitamin C Deficiency (Scurvy)

• Easy bruising and bleeding, teeth and gum disease, hair loss.
• Treated with vitamin C supplements.
• Symptoms such as joint pain usually resolve within 48 hours.
• Full recovery usually takes two weeks.

Vitamin B1 (Thiamine)

• Exists as free form, monophosphate (TMP), triphosphate (TTP), and pyrophosphate (TPP).
• Coenzyme in the production of energy from nutrients.
  • Transketolase − pentose phosphate pathway
  • Pyruvate dehydrogenase
  • α−ketoglutarate dehydrogenase

Thiamine Deficiency

• Fatigue, irritability, poor memory, loss of appetite, sleep disturbances, abdominal discomfort, and weight loss.
• May lead to a severe thiamine deficiency (beriberi) with nerve, heart, and brain abnormalities.

Vitamin B2 (Riboflavin)

• Important in energy production, carbohydrate, fat, and protein metabolism, and formation of antibodies and red blood cells.
• Central component of the cofactor (FAD).

Vitamin B2 Deficiency

• Sore throat, sore tongue, sore mouth, and sore corners of lips

Vitamin B3 (Niacin)

• Also known as nicotinic acid.
• Acts as coenzymes to more than 200 enzymes involved in redox reactions.
• NAD and NADP production.

Vitamin B3 Deficiency (Pellagra)

• Diarrhea
• Dementia
• Dermatitis

Vitamin B6

• Pyridoxine/Pyridoxal/Pyridoxamine
• Pyridoxal-5′-phosphate cofactor for amino acid metabolism (transamination, deamination, decarboxylation).
• Conversion of tryptophan to niacin.
• Release of glucose from glycogen; haem synthesis.

Vitamin B12 (Cobalamin)

• Released from food by stomach acid and enzymes; binds to proteins.
• Pancreatic enzymes degrade proteins releasing vitamin B12, which then binds to the intrinsic factor (IF), secreted by the stomach.
• In the small intestine, receptors take up the vit B12-IF complex in the presence of calcium supplied by the pancreas. – 1% of Vitamin B12 can be absorbed passively.

Vitamin B12 Deficiency

• Pernicious anemia
• Autoimmune destruction of IF-producing cells in the stomach.
• Malabsorption
• Lack of stomach acid and pancreatic disease, resulting in neurologic symptoms.

Folate

• Coenzyme in methylation reactions and DNA synthesis.
• Many foods are fortified with folic acid.
• Higher requirements during pregnancy.

Folate Deficiency

• Causes:
  • Malabsorption.
  • Drugs that interfere with folic acid metabolism.
  • Disease states increasing cell turnover (e.g., leukemia, hemolytic anemias).
• Symptoms:
  • Increased cardiovascular disease risk.
  • Macrocytic anemia (lethargy, weakness).
  • Fetal developmental abnormalities.

Biotin

• Required for cell growth, fat and amino acid metabolism.
• Cofactor for carbon dioxide transfer in several carboxylase enzymes.
• Deficiency is rare as gut flora produce biotin in excess of daily requirements.
• Number of metabolic disorders where problems exist with biotin use.

This quiz covers the essential information about vitamins, including their classifications as fat-soluble and water-soluble vitamins. You'll learn about the importance of vitamins, their functions in the body, and the consequences of deficiencies. Test your knowledge on various vitamins and their roles in human health.