Water-Soluble Vitamins: B Complex and C

Water-Soluble Vitamins Overview & B1 - Nerve Nourisher

• General WSV Properties: Absorbed via active/facilitated transport; minimal body storage (except B12); excess excreted in urine; low toxicity risk.
• Thiamine (B1):
  • Active form: Thiamine Pyrophosphate (TPP).
  • TPP is coenzyme for (📌 ATP-B):
    • Pyruvate dehydrogenase (PDH)
    • α-ketoglutarate dehydrogenase (α-KGDH)
    • Transketolase (HMP shunt)
    • Branched-chain ketoacid dehydrogenase (BCKDH)
  • Deficiency:
    • Beriberi: Dry (polyneuropathy); Wet (cardiac failure, edema).
    • Wernicke-Korsakoff Syndrome: Wernicke's (📌 COA: Confusion, Ophthalmoplegia, Ataxia); Korsakoff's (amnesia, confabulation).
  • Sources: Whole grains, pork. RDA: ~1.2 mg/day. structure and Beriberi clinical presentation)

⭐ Activity of erythrocyte transketolase is a reliable index of thiamine status.

B2 (Riboflavin) & B3 (Niacin) - Electron Shuttlers

• B2 (Riboflavin)

  • Active forms: Flavin Mononucleotide ($FMN$), Flavin Adenine Dinucleotide ($FAD$).
  • Role: Key in redox reactions (e.g., succinate dehydrogenase in TCA cycle).
  • Deficiency (Ariboflavinosis): Cheilosis, angular stomatitis, glossitis, seborrheic dermatitis, corneal vascularization.

• B3 (Niacin)

  • Active forms: Nicotinamide Adenine Dinucleotide ($NAD^+$), Nicotinamide Adenine Dinucleotide Phosphate ($NADP^+$).
  • Role: Central to redox reactions. Synthesized from Tryptophan.

    ⭐ About 60 mg of tryptophan is equivalent to 1 mg of niacin.

  • Deficiency (Pellagra): 📌 3Ds: Dermatitis (photosensitive), Diarrhea, Dementia; Death if severe.
    • Causes: Hartnup disease, carcinoid syndrome, isoniazid use.
  • Uses: Treats hyperlipidemia. Toxicity: Niacin flush (prostaglandin-mediated).

B5 (Pantothenate) & B6 (Pyridoxine) - Acyl & Amino Aces

• B5 (Pantothenic Acid):
  • Component: Coenzyme A (CoA), Acyl Carrier Protein (ACP).
  • Role: Acyl transfer reactions; key in fatty acid synthesis/oxidation.
  • Deficiency: Rare; Burning feet syndrome.
• B6 (Pyridoxine): Active form: Pyridoxal Phosphate (PLP).
  • Role: Amino acid metabolism (transamination, decarboxylation); neurotransmitter & heme synthesis; glycogenolysis.
  • Deficiency: Peripheral neuropathy, sideroblastic anemia, convulsions (especially infants).
  • Drug Interactions: Isoniazid, Penicillamine (can cause deficiency).
  • Toxicity: Sensory neuropathy with high doses.

⭐ Isoniazid therapy can lead to Vitamin B6 deficiency by forming an inactive derivative with PLP.

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B7 (Biotin), B9 (Folate) & B12 (Cobalamin) - One-Carbon & Cell Crafters

Biotin (B7): "Biotin for Carboxylation" 📌

• Coenzyme: Pyruvate carboxylase, Acetyl-CoA carboxylase, Propionyl-CoA carboxylase.
• Deficiency (rare): Avidin (raw eggs), antibiotics → dermatitis, alopecia.

Folate (B9): "Folate for Formation (DNA)" 📌

• Active: Tetrahydrofolate (THF). One-carbon transfers for DNA (purines, thymidylate) synthesis.
• Deficiency: Megaloblastic anemia (MCV > 100), ↑homocysteine, neural tube defects. Folate trap (B12 def.).

Cobalamin (B12): "B12 for Brain & Blood" 📌

• Cobalt; Intrinsic Factor for absorption.
• Reactions:
  • Homocysteine $\xrightarrow{B12, THF}$ Methionine
  • Methylmalonyl-CoA $\xrightarrow{B12}$ Succinyl-CoA
• Deficiency: Megaloblastic anemia, pernicious anemia, neurological (SCD), ↑homocysteine & ↑methylmalonic acid (MMA).

⭐ Elevated serum methylmalonic acid and homocysteine levels are characteristic of Vitamin B12 deficiency, whereas only homocysteine is elevated in folate deficiency.

Vitamin C (Ascorbic Acid) - Collagen & Antioxidant Champion

• Chemistry & Sources: Ascorbic acid. Sources: Citrus fruits (amla, lemon), guava, green leafy vegetables. RDA: 60-90 mg/day.
• Key Functions:
  • Antioxidant (regenerates Vitamin E).
  • Collagen synthesis (hydroxylation of proline & lysine).
  • ↑ Non-heme iron absorption.
  • Carnitine & norepinephrine synthesis.
  • Immune support.
• Deficiency (Scurvy):
  • Impaired wound healing, bleeding gums (gingivitis).
  • Perifollicular hemorrhages, corkscrew hairs, arthralgia.
• Toxicity: GI upset, nausea, diarrhea; oxalate kidney stones with high doses (> 2 g/day).

⭐ Vitamin C is essential for the hydroxylation of proline and lysine residues in procollagen, a key step in collagen synthesis.

High‑Yield Points - ⚡ Biggest Takeaways

• Thiamine (B1) deficiency: Beriberi, Wernicke-Korsakoff syndrome. Coenzyme: TPP.
• Riboflavin (B2) deficiency: Oral-ocular-genital syndrome. Coenzymes: FAD, FMN.
• Niacin (B3) deficiency: Pellagra (4Ds). Synthesized from tryptophan.
• Pyridoxine (B6) deficiency: Peripheral neuropathy, sideroblastic anemia. Isoniazid induces deficiency.
• Folate (B9) deficiency: Megaloblastic anemia, neural tube defects.
• Cobalamin (B12) deficiency: Megaloblastic anemia, neurological deficits. Requires intrinsic factor.
• Vitamin C (Ascorbic acid) deficiency: Scurvy. Essential for collagen synthesis, enhances iron absorption.