8. Thiamine (Vitamin B1) | Functions, Beriberi, Wernicke–Korsakoff Syndrome MBBS Biochemistry USMLE

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Thiamine (Vitamin B1) | Functions, Beriberi, Wernicke–Korsakoff Syndrome | MBBS Biochemistry | USMLE Step 1

👋 Hello future doctors and biochem learners! Thiamine (Vitamin B1) is the “energy vitamin”, essential as a coenzyme in carbohydrate metabolism. Its deficiency leads to the classic disorders Beriberi and Wernicke–Korsakoff syndrome, which are favorite exam questions in MBBS, NEET PG, FMGE, and USMLE Step 1.

This lecture covers the chemistry, absorption, coenzyme role, deficiency features, and clinical aspects of Thiamine (Vitamin B1). 🧬📚

🌟 Chemistry & Sources

Water-soluble vitamin.

Active form: Thiamine Pyrophosphate (TPP).

Sources: Whole grains, legumes, nuts, pork, yeast.

Easily destroyed by heat (cooking).

🌟 Absorption, Transport & Storage

Absorbed in jejunum/ileum.

Transported freely in plasma or bound to albumin.

Small body stores → deficiency appears quickly if intake is low.

🌟 Functions (Coenzyme Roles of TPP)

1️⃣ Pyruvate Dehydrogenase Complex: Links glycolysis → TCA cycle.
2️⃣ α-Ketoglutarate Dehydrogenase: TCA cycle.
3️⃣ Branched-chain α-ketoacid Dehydrogenase: BCAA metabolism.
4️⃣ Transketolase: HMP shunt (important for NADPH production).

👉 Mnemonic: “ATP” → α-ketoglutarate dehydrogenase, Transketolase, Pyruvate dehydrogenase.

🌟 Deficiency of Thiamine

1️⃣ Beriberi

Dry Beriberi: Peripheral neuropathy, muscle wasting, foot drop, wrist drop.

Wet Beriberi: Cardiac failure, dilated cardiomyopathy, edema.

Seen in malnutrition, polished rice diet.

2️⃣ Wernicke–Korsakoff Syndrome

Common in chronic alcoholics (poor intake + impaired absorption).

Wernicke’s Triad: Confusion, Ataxia, Ophthalmoplegia.

Korsakoff’s features: Memory loss, confabulation, psychosis.

Exam clue: Symptoms improve with thiamine administration.

Diagnostic: RBC transketolase activity ↑ after thiamine.

🌟 Toxicity

Rare (water-soluble).

Excess excreted in urine.

🩺 Clinical Aspects

Thiamine supplementation: given before glucose in alcoholics to prevent precipitating Wernicke’s encephalopathy.

Infantile Beriberi: Breastfed infants of deficient mothers → tachycardia, edema, cyanosis.

🎯 Exam Integration

Coenzyme = TPP.

Deficiency = Beriberi + Wernicke–Korsakoff.

Enzyme test = RBC transketolase activity.
👉 Classic exam vignette: “Alcoholic with confusion, ataxia, eye signs → treat with Thiamine before glucose.”

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❓Should we make the next lecture on Vitamin B2 (Riboflavin – FMN, FAD, angular cheilitis, glossitis) to continue the Water-Soluble Vitamins series? Drop your request in the comments below! 😊

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