Vitamins

Question 1

Fat Soluble Vitamins

Answer 1

• A, D, E, K
• Absorption dependent on gut (ileum) and pancreas
• Toxicity more common than for water-soluble vitamins, because these accumulate in fat.
• Malabsorption syndromes (steatorrhea), such as CF and sprue, or mineral oil intake can cause fat-soluble vitamin deficiencies.

Question 2

Water-soluble vitamins

Answer 2

• B1 (thiamine: TPP)
• B2 (riboflavin: FAD, FMN)
• B3 (niacin: NAD+)
• B5 (pantothenic acid: CoA)
• B6 (pyridoxine: PLP)
• B7 (biotin)
• B9 (folate)
• B12 (cobalamin)
• C (ascorbic acid)
  All washed out easily from body except B12 and folate (stored in the liver.
  B-complex deficiencies often result in dermatitis, glossitis, and diarrhea.

Question 3

Vitamin A (retinol)

Answer 3

Function: Antioxidant, constituent of visual pigments; essential for differentiation of epithelial cells into specialized tissue; prevents squamous metaplasia. Used to treat measles and AML subtype M3.
Deficiency: night blindness, dry skin
Excess: skin changes, teratogenic

Question 4

Vitamin B1 (thiamine)

Answer 4

Function: In TPP, a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase, branched chain amino acid dehydrogenase
Deficiency: ATP depletion worsened by glucose infusion; highly aerobic tissues (brain and heart) are affected first. Causes Wernicke-Korsakoff Syndrome and beriberi. Seen in malnutrition and alcoholism.

Question 5

Wernicke-Korsakoff

Answer 5

Confusion, ophthalmoplegia, ataxia (classic triad) + confabulation, personality change, memory loss (permanent). Damage to medial dorsal nucleus of thalamus, mammillary bodies.

Question 6

Dry beriberi

Answer 6

Polyneuritis, symmetrical muscle wasting

Question 7

Wet beriberi

Answer 7

High-output cardiac failure (dilated cardiomyopathy), edema

Question 8

Vitamin B2 (riboflavin)

Answer 8

Function: Cofactor in oxidation and reduction (e.g., FADH2)
Deficiency: the 2 C’s of B2, Cheilosis (inflammation of lips, scaling and fissures at the corners of the mouth, and Corneal vascularization.

Question 9

Vitamin B3 (niacin)

Answer 9

Function: Constituent of NAD+, NADP+ (used in redox reactions). Derived from tryptophan. Synthesis requires B6.
Deficiency: Glossitis, pellagra (3 D’s of B3: diarrhea, dermatitis, dementia).
Excess: Facial flushing (due to pharmacologic doses for treatment of hyperlipidemia).

Question 10

Vitamin B5 (pantothenate)

Answer 10

Function: Essential component of CoA (a cofactor for acyl transfers) and fatty acid synthase.
Deficiency: Dermatitis, enteritis, alopecia, adrenal insufficiency.

Question 11

Vitamin B6 (pyridoxine)

Answer 11

Function: Converted to pyridoxal phosphate, a cofactor for transamination (AST, ALT), decarboxylation reactions, glycogen phosphorylase. Synthesis of cystathionine, heme, niacin, histamine, serotonin, epinephrine, NE, and GABA.
Deficiency: Convulsions, hyperirritability, peripheral neuropathy (inducible by INH and OCPs), sideroblastic anemias (due to impaired hemoglobin synthesis and iron excess)

Question 12

Vitamin B7 (biotin)

Answer 12

Function: Cofactor for carboxylation enzymes (which add a 1-C group): pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase
Deficiency: Relatively rare. Dermatitis, alopecia, enteritis. Caused by antibiotic use or excessive ingestion of raw eggs (avidin in egg whites avidly binds biotin)

Question 13

Vitamin B9 (folic acid)

Answer 13

Function: Converted to THF, a coenzyme for 1-carbon transfer/methylation reactions. Important for synthesis of nitrogenous bases in DNA and RNA.
Deficiency: Macrocytic, megaloblastic anemia; NO neurologic symptoms. Most common vitamin deficiency in U.S. Seen in alcoholism and pregnancy.
Factoids: Found in leafy green vegetables. Small reserve pool stored mainly in liver. Supplemental folic acid in pregnancy reduces neural tube defects.

Question 14

Vitamin B12 (cobalamin)

Answer 14

Function: Cofactor for homocysteine methyltransferase and methylmalonyl-CoA mutase.
Deficiency: Macrocytic, megaloblastic anemia, hypersegmented PMNs, neurologic Sx (paresthesias, subacute combined degeneration) due to abnormal myelin. Prolonged deficiency leads to irreversible NS damage.
Factoids: Found in animal products. Synthesized only by microorganisms. Very large reserve pool (years) in the liver. Deficiency usually caused by malabsorption (sprue, enteritis, tapeworm), lack of intrinsic factor (pernicious anemia, gastric bypass), or absence of terminal ileum (Crohn’s disease). Elevated MM-CoA and Homocysteine.

Question 15

Vitamin C (ascorbic acid)

Answer 15

Function: Antioxidant, facilitates iron absorption, hydroxylation of proline and lysine in collagen synthesis, conversion of dopamine to NE by dopamine-B-hydroxylase
Deficiency: Scurvy (swollen gums, bruising, hemarthrosis, anemia, poor wound healing); weakened immune response.
Excess: Nausea, vomiting, diarrhea, fatigue, sleep problems. Increased risk of iron toxicity (e.g., transfusions, hereditary hemochromatosis).

Question 16

Vitamin D

Answer 16

Factoids: D2 = ergocalciferol from plants; D3 = cholecalciferol from milk, sun exposure
Function: Increased intestinal absorption of Ca and phosphate, bone mineralization
Deficiency: Rickets in children (bone pain and deformity), osteomalacia in adults (bone pain and muscle weakness), hypocalcemic tetany. Breast milk has low vitamin D (supplement in dark-skinned infants)
Excess: Hypercalcemia, hypercalciuria, loss of appetite, stupor. Seen in sarcoidosis (increased activation of vitamin D by epithelioid macrophages).

Question 17

Vitamin E

Answer 17

Function: Antioxidant (protects erythrocytes and membranes from free-radical damage).
Deficiency: Increased fragility of erythrocytes (hemolytic anemia), muscle weakness, posterior column and spinocerebellar tract demyelination (resembles Friedrich’s ataxia).

Question 18

Vitamin K

Answer 18

Function: Gamma carboxylation of glutamic acid residues on various proteins concerned with blood clotting. Synthesized by intestinal flora.
Deficiency: Neonatal hemorrhage with increased PT and PTT but normal bleeding time. Can also occur after prolonged use of broad-spectrum antibiotics.
Factoids: Necessary for synthesis of clotting factors II, VII, IX, X and proteins C and S. Warfarin is a vitamin K antagonist. Not in breast milk; neonates are given vitamin K injection at birth to prevent hemorrhage. Non-acute treatment of warfarin OD/bleed.