Nutrition: Vitamins Overview Quiz

Vitamins

• Vitamins are organic compounds needed by humans in small amounts
• They are not produced in adequate quantities by the body and must be obtained from the diet.
• Vitamins are classified as water-soluble or fat-soluble.

Water-Soluble Vitamins

• Water-soluble vitamins are easily excreted in urine and do not typically accumulate in the body.
• Deficiencies can develop quickly.
• Examples include folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid.

Fat-Soluble Vitamins

• Fat-soluble vitamins are absorbed, transported, and stored with dietary fat.
• They are not readily excreted, so significant amounts can accumulate in the liver and adipose tissue.
• Deficiencies can take years to develop.
• Examples include vitamins A, D, K, and E.

Vitamin C

• Ascorbic acid, the active form, is a crucial reducing agent in the body.
• It's a coenzyme in hydroxylation reactions, required for connective tissue (collagen) synthesis and wound healing.
• Vitamin C facilitates the absorption of non-heme iron in the digestive tract.
• Deficiency results in scurvy, a condition characterized by sore gums, loose teeth, fragile blood vessels, hemorrhage, swollen joints, and fatigue, defective connective tissue, and microcytic anemia.

Folic Acid

• Tetrahydrofolate (THF) is the reduced coenzyme form crucial for one-carbon metabolism.
• It receives one-carbon fragments from various donors, transferring them to intermediates in the synthesis of amino acids, purine nucleotides, and the pyrimidine nucleotide thymidylate.
• A deficiency can result in megaloblastic anemia due to diminished synthesis of purine nucleotides and TMP.
• This will also impair cell division.
• Common causes include increased demand (pregnancy/lactation), malabsorption, alcoholism, and drugs like methotrexate.

Vitamin B12

• Vitamin B12 is synthesized exclusively by microorganisms and is not present in plants.
• It acts as a coenzyme in two essential reactions:
• re-methylation of homocysteine (Hcy) to methionine.
• isomerization of methylmalonyl coenzyme A (MMA) to succinyl CoA.
• B12 deficiencies result in unusual branched-fatty acids accumulating in cell membranes, especially in the nervous system.
• It's crucial for the proper functioning of the central nervous system.
• Vitamin B12 is absorbed in the stomach and intestines, requiring intrinsic factor.
• Deficiency can be caused by insufficient intake, malabsorption issues such as pernicious anemia (lack of intrinsic factor) or gastrectomy, and increased demand (pregnancy/lactation).

Folate Trap in Vitamin B12 Deficiency

• Folate cannot be converted to other THF forms, the N5-methyl form accumulates,
• The levels of other THF forms decrease, resulting in a deficient supply of the required THF forms for cellular function.

Vitamin B12 Deficiency

• In contrast to other water-soluble vitamins, vitamin B12 stores are significant and can last for years, resulting in a delayed onset of deficiency symptoms
• May be caused by reduced intake, increased demands (pregnancy/lactation); or malabsorption problems (pernicious anemia).
• Symptoms can be lifelong if untreated, and often include neurological manifestations.

Absorption of Vitamin B12

• B12 is released in the stomach from food.
• It binds to R-protein/haptocorrin.
• The complex moves through the intestine.
• Pancreatic enzymes release B12 from R-protein.
• B12 binds to intrinsic factor (IF).
• The cobalamin-intrinsic factor complex (B12-IF complex) is formed.
• The complex travels through the intestines and binds to a receptor.
• Cobalamin (B12 in the complex) enters the mucosal cell then the circulatory system and is stored in the liver.
• B12 is released into bile and efficiently reabsorbed.

Pernicious Anemia

• An autoimmune condition where the stomach's parietal cells are destroyed (lack of IF).
• B12 cannot be absorbed.
• Patients with prior gastric surgery (or gastrectomy) are at risk.
• Deficiency can cause various neurological and psychological symptoms.

Pyridoxine (Vitamin B6)

• Includes pyridoxine, pyridoxal, and pyridoxamine.
• All have a pyridine ring, but differ in the functional group.
• Exists as pyridoxal phosphate (PLP), the biologically active coenzyme.
• PLP is a coenzyme for many enzymes involved in amino acid metabolism.
• Deficiency is rare but can be observed in malnourished infants, women on oral contraceptives; and those with alcoholism.
• Toxicity observed at higher doses (over dietary recommendations).

Thiamine (Vitamin B1)

• Exists as thiamine pyrophosphate (TPP), the active form of the molecule.
• TPP is crucial in carbohydrate metabolism, oxidative decarboxylation of pyruvates and a-ketoglutarate;
• Essential for proper function of the central nervous system.
• Deficiency results in symptoms such as beriberi and Wernicke-Korsakoff syndrome (typically associated with chronic alcohol abuse).

Niacin (Vitamin B3)

• Exists as nicotinamide adenine dinucleotide (NAD+), and its phosphorylated derivative, nicotinamide adenine dinucleotide phosphate (NADP+).
• These are important coenzymes in oxidation-reduction reactions.
• Can be synthesized from the amino acid tryptophan.
• Deficiency leads to pellagra (with symptoms of dermatitis, diarrhea, and dementia),
• Toxicity arises at high dosage.

Riboflavin (Vitamin B2)

• Active forms include flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
• FMN and FAD are crucial for oxidation-reduction reactions.
• deficiency does not result in major diseases typically.

Biotin (Vitamin B7)

• A carrier of activated carbon dioxide in various carboxylation reactions, such as the synthesis of fatty acids and amino acids.
• Biotinidase is enzyme necessary for recycling of biotin, and deficiency is a notable cause of newborn screening tests.
• Dietary biotin deficiency can be induced through dietary restrictions.

Pantothenic Acid (Vitamin B5)

• A component of coenzyme A (CoA) essential in acyl group transfer.
• Also involved in fatty acid synthesis pathways.
• Deficiencies don't appear to be common.

Vitamin D

• Vitamin D is a group of sterols with hormone-like functions.
• The active form is 1,25-dihydroxycholecalciferol (calcitriol).
• Calcitriol regulates calcium and phosphorus levels through effects on the intestines, kidneys, and bone.
• Vitamin D is synthesized in the skin via UV light exposure.

Vitamin K

• Functions in post-translational modification of proteins, notably in blood clotting (glutamic acid residues).
• Vitamin K, exists in plant (phylloquinone (K1)) and microbial (menaquinone (K2)) form. - Deficiency in infants is common due to their sterile gut; bacterial production is missing, and this is remedied by injection.
• Warfarin, an anticoagulant, inhibits Vitamin K epoxide reductase.

Vitamin E

• A group of tocopherols with antioxidant activity, primarily a-tocopherol.
• Protects against non-enzymatic oxidation.
• regeneration of vitamin E active form is important.

Vitamin A

• Retinol is the preformed vitamin.
• also exists as retinoids- retinoids include naturally occurring forms of Vitamin A (retinol and metabolites) and synthetic forms (drugs
• retinoids function in vision, reproduction, tissue growth and maintainence of epithelial tissue.
• deficiency may cause night blindness.
• Toxic effects at high dosage (e.g., liver enlargement).