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Vitamin B1 (thiamine) - Deficiency - Impaired glucose breakdown p ATP depletion worsened by glucose infusion; highly aerobic tissues (eg, brain, heart) are affected first. In alcoholic or malnourished patients, give thiamine before dextrose to reduce risk of precipitating Wernicke encephalopathy....

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  • August 17, 2024
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  • 2024/2025
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FIRST AID USMLE STEP 1 - VITAMINS
Vitamin B1 (thiamine) - Deficiency - Impaired glucose breakdown p ATP depletion worsened by
glucose infusion; highly aerobic tissues (eg, brain, heart) are affected first. In alcoholic or malnourished
patients, give thiamine before dextrose to reduce risk of precipitating Wernicke encephalopathy.
Diagnosis made by increase in RBC transketolase activity following vitamin B1 administration



Vitamin A (retinol) - Excess - Acute toxicity—nausea, vomiting, vertigo, and blurred vision. Chronic
toxicity—alopecia, dry skin (eg, scaliness), hepatic toxicity and enlargement, arthralgias, and
pseudotumor cerebri. Teratogenic (cleft palate, cardiac abnormalities), therefore a ⊝ pregnancy test and
two forms of contraception are required before isotretinoin (vitamin A derivative) is prescribed.



Vitamin A (retinol) - Function - Antioxidant; constituent of visual pigments (retinal); essential for
normal differentiation of epithelial cells into specialized tissue (pancreatic cells, mucus-secreting cells);
prevents squamous metaplasia. Used to treat measles and acute promyelocytic leukemia (APL).

.



Vitamin B1 (thiamine) - Extra - Think ATP: α-ketoglutarate dehydrogenase, Transketolase, and
Pyruvate dehydrogenase. Spell beriberi as Ber1Ber1 to remember vitamin B1. Wernicke-Korsakoff
syndrome —confusion, ophthalmoplegia, ataxia (classic triad) + confabulation, personality change,
memory loss (permanent). Damage to medial dorsal nucleus of thalamus, mammillary bodies. Dry
beriberi —polyneuritis, symmetrical muscle wasting. Wet beriberi —high-output cardiac failure (dilated
cardiomyopathy), edema.



Vitamin B1 (thiamine) - Function - In thiamine pyrophosphate (TPP), a cofactor for several
dehydrogenase enzyme reactions: +Pyruvate dehydrogenase (links glycolysis to TCA cycle) +α-
ketoglutarate dehydrogenase (TCA cycle) +Transketolase (HMP shunt) +Branched-chain ketoacid
dehydrogenase



Vitamin B12 (cobalamin) - Deficiency - Macrocytic, megaloblastic anemia; hypersegmented PMNs;
paresthesias and subacute combined degeneration (degeneration of dorsal columns, lateral corticospinal
tracts, and spinocerebellar tracts) due to abnormal myelin. Associated with increased serum
homocysteine and methylmalonic acid levels, along with 2° folate deficiency. Prolonged deficiency ->
irreversible nerve damage.

, Vitamin B12 (cobalamin) - Extra - Found in animal products. Synthesized only by microorganisms.
Very large reserve pool (several years) stored primarily in the liver. Deficiency caused by malabsorption
(eg, sprue, enteritis, Diphyllobothrium latum ), lack of intrinsic factor (pernicious anemia, gastric bypass
surgery), absence of terminal ileum (surgical resection, eg, for Crohn disease), or insufficient intake (eg,
veganism). Anti-intrinsic factor antibodies diagnostic for pernicious anemia.

Vitamin A (retinol) - Deficiency - Night blindness (nyctalopia); dry, scaly skin (xerosis cutis); corneal
degeneration (keratomalacia); Bitot spots on conjunctiva; immunosuppression.



Vitamin B12 (cobalamin) - Function - Cofactor for methionine synthase (transfers CH3 groups as
methylcobalamin) and methylmalonyl-CoA mutase. Important for DNA synthesis.



Vitamin B2 (riboflavin) - Deficiency - Cheilosis (inflammation of lips, scaling and fissures at the
corners of the mouth), Corneal vascularization.



Vitamin B2 (riboflavin) - Extra - FAD and FMN are derived from riboFlavin (B2 ≈ 2 ATP). The 2 C's of
B2 .



Vitamin B2 (riboflavin) - Function - Component of flavins FAD and FMN, used as cofactors in redox
reactions, eg, the succinate dehydrogenase reaction in the TCA cycle.



Vitamin B3 (niacin) - Deficiency - Glossitis. Severe deficiency leads to pellagra, which can be
caused by Hartnup disease, malignant carcinoid syndrome ( increased tryptophan metabolism), and
isoniazid ( decreased vitamin B6). Symptoms of pellagra: Diarrhea, Dementia (also hallucinations) ,
Dermatitis (C3/C4 dermatome circumferential "broad collar" rash [Casal necklace], hyperpigmentation of
sun- exposed limbs A ).



Vitamin B3 (niacin) - Excess - Facial flushing (induced by prostaglandin, not histamine; can avoid
by taking aspirin with niacin), hyperglycemia, hyperuricemia.



Vitamin B3 (niacin) - Extra - NAD derived from Niacin (B3 ≈ 3 ATP). The 3 D's of B3 . Hartnup
disease —autosomal recessive. Deficiency of neutral amino acid (eg, tryptophan) transporters in
proximal renal tubular cells and on enterocytes -> neutral aminoaciduria and decreased absorption from
the gut -> increased tryptophan for conversion to niacin -> pellagra-like symptoms. Treat with high-
protein diet and nicotinic acid

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