VITAMIN
FUNCTION
DEFICIENCY
CAUSE · CLUE
Cofactor for carboxylases: pyruvate → oxaloacetate, acetyl-CoA → malonyl-CoA, propionyl-CoA → methylmalonyl-CoA
Dermatitis, alopecia, enteritis, lactic acidosis
Raw egg whites (avidin binds biotin), long-term antibiotics
THF carries one-carbon units for purine and thymidine synthesis; absorbed in jejunum
Megaloblastic anemia, hypersegmented neutrophils, glossitis, no neuro signs; ↑ homocysteine, normal MMA
Alcohol, pregnancy, poor diet, MTX, trimethoprim, phenytoin, sulfa · neural tube defects if low early in pregnancy
Methionine synthase (homocysteine → methionine, regenerates THF) · methylmalonyl-CoA mutase (MMA → succinyl-CoA)
Megaloblastic anemia + neuro: subacute combined degeneration (dorsal columns, lateral CST, spinocerebellar), peripheral neuropathy, dementia; ↑ homocysteine, ↑ MMA
Pernicious anemia (anti-IF, anti-parietal cell), gastrectomy, ileal resection/Crohn, vegan diet, D latum, metformin, PPIs
Freed by acid/pepsin → R-binder → pancreatic proteases release → intrinsic factor → terminal ileum
Any step can fail
Pancreatic insufficiency also ↓ B12
Without B12, folate stays stuck as N⁵-methyl-THF
Functional folate deficiency
Folate fixes the anemia but not the nerves — never give folate alone if B12 low
Vitamin C — ascorbic acid
Prolyl/lysyl hydroxylation (collagen), keeps iron Fe²⁺ (↑ absorption), dopamine → norepinephrine (dopamine β-hydroxylase)
Scurvy: swollen bleeding gums, perifollicular hemorrhages, corkscrew hairs, bruising, poor healing, anemia, hemarthrosis
Tea-and-toast elderly, restrictive diets · excess → oxalate stones, ↑ iron absorption (hemochromatosis)
Methemoglobinemia treatment
Vitamin C reduces Fe³⁺ → Fe²⁺
—
Methylene blue first-line; vitamin C as adjunct
Needs B12 + folate (→ methionine) or B6 (→ cystathionine)
↑ Homocysteine → thrombosis, atherosclerosis
Also ↑ in homocystinuria (9.04)