Vitamin deficiencies

Question 1

Vitamin A (retinol)

Answer 1

Function: antioxidant, essential for normal differentiation of epithelial cells into specialized tissue

Deficiency: Night blindness, dry scaly skin, alopecia, corneal degeneration (keratomalacia), immune suppression (vulnerability to measles)

Excess: Teratogen

Question 2

Vitamin B1 (thiamine)

Answer 2

Function: thiamine pyrophosphate (TPP) is a cofactor for several dehydrogenase rxns:

• Pyruvate dehydrogenase
• Alpha-ketoglutarate dehydrogenase in TCA cycle
• Transketolase in HMP shunt
• Branched-chain ketoacid dehydrogenase in metabolism of valine, isoleucine, and leucine

Deficiency (alcohol interferes with absorption):

• Impaired glucose breakdown
• Wernicke-Korsakoff syndrome
• Infantile beriberi (fulminant cardiac syndrome)
• Adult beriberi (dry beriberi characterized by symmetrical peripheral neuropathy of distal extremities; wet beriberi characterized by neuropathy and cardiomegaly)

Question 3

Vitamin B2 (riboflavin)

Answer 3

Function: FAD and FMN used as cofactors in redox rxns

Deficiency: Cheilosis (inflammation of lips, scaling and fissures at corners of the mouth); Corneal neovascularization; Magenta-colored tongue

Question 4

Vitamin B3 (niacin)

Answer 4

Function: NAD+ and NADP+ used in redox rxns

Derived from tryptophan (Hartnup disease –> deficiency); synthesis requires Vit B2 & B6

Deficiency: Pellagra (Diarrhea, Dementia, Dermatitis)

Excess: Flushing, hyperglycemia, hyperuricemia

Question 5

Vitamin B5 (pantothenate)

Answer 5

Function: component of coenzyme A:

• Fatty acid synthase
• Fatty acyl CoA synthetase
• Pyruvate dehydrogenase
• alpha-ketoglutarate dehydrogenase (TCA cycle)

Question 6

Vitamin B6 (pyridoxine)

Answer 6

Function: Pyridoxal phosphate used in aminotransferases (protein catabolism) and in aminolevulinate synthase (heme synthesis); used in synthesis of heme, niacin, histamine, serotonin, epi, norepi, dopamine, GABA

Deficiency: sideroblastic anemia, convulsions, hyperirritability, cheilosperipheral neuropathy

Most common cause of deficit is isoniazid therapy

Question 7

Vitamin B7 (biotin)

Answer 7

Function: cofactor for decarboxylation:

• Pyruvate carboxylase (gluconeogenesis)
• Acetyl-CoA carboxylase (fatty acid synthesis)
• Propionyl-CoA carboxylase (odd-chain fatty acids, Val, Met, Ile, Thr)

Most common cause of deficiency - excessive consumption of eggs (avidin is a biotin-binding protein)

Deficiency: alopecia, bowel inflammation, muscle pain

Question 8

Vitamin B9 (folate)

Answer 8

Function: THF is a coenzyme used in methylation reactions; important for synthesis of purines (A,G) and thymidine (pyrimidine)

Most common cause of deficiency - alcoholics and pregnancy

Deficiency: macrocytic megaloblastic anemia; homocystinemia with risk of DVT and atherosclerosis; neural tube defects in fetus

Question 9

Vitamin B12 (cobalamin)

Answer 9

Function: cofactor for homocysteine methyltransferase (produces methionine, SAM) and methylmalonyl-CoA mutase (odd chain fatty acids)

Most common cause of deficiency - pernicious anemia

Deficiency: macrocystic megaloblastic anemia; atrophic glossitis, parethesias and subacute combined degeneration due to abnormal myelin (shuffling broad-based gait)

Question 10

Vitamin C (ascorbic acid)

Answer 10

Function: prolyl and lysyl hydroxylases (collagen synthesis), dopamine hydroxylase (catecholamine synthesis), reduces iron to Fe+2 state to facilitate absorption

Deficiency: Increased BT, Normal PT; scurvy (swollen gums, bruising, hemarthorsis, anemia, poor wound healing, perifollicular and subperiosteal hemorrhages, corkscrew hair)

Excess: calcium oxalate nephrolithiasis

Question 11

Vitamin D

Answer 11

Function: increases intestinal absorption of calcium and phosphate, increases bone mineralization

Deficiency: Rickets, osteomalacia, hypocalcemic tetany

Question 12

Vitamin E (tocopherol/tocotrienol)

Answer 12

Function: antioxidant (protects membrane lipids from peroxidation; helps prevent the formation of fatty streaks)

Deficiency: hemolytic anemia, posterior column and spinocerebellar tract demyelination

Question 13

Vitamin K

Answer 13

Function: cofactor for gamma-carboxylation of glutamate on factors II, VII, IX, X, and proteins C and S

Deficiency: Increased PT/PTT but normal BT; hemorrhagic disease

Question 14

Zinc

Answer 14

Function: Transcription factor motif (zinc fingers), cofactor in many enzymatic rxns Deficiency: delayed wound healing, hypogonadism, alopecia, dysgeusia, anosomia, acrodermatitis enteropathica