Vitamins Quiz: C, B9, and B1 Insights

Vitamins II: Water Soluble Vitamins

• Learning Objectives: Identify water-soluble vitamins, state their functions, understand associated deficiencies, and enumerate their clinical indications.

Classification

• Water-Soluble Vitamins:

  • Non-B complex: Ascorbic acid (vitamin C)
  • B Complex:
    • Energy releasing: Thiamine (vitamin B₁), Riboflavin (vitamin B₂), Niacin (vitamin B₃), Pantothenic acid (vitamin B₅), Biotin (vitamin B₇)
    • Hematopoietic: Riboflavin (vitamin B₂), Niacin (vitamin B₃), Pantothenic acid (vitamin B₅), Pyridoxine (vitamin B₆), Folate (vitamin B₉), Cobalamin (vitamin B₁₂)
    • Other: Pyridoxine (vitamin B₆), Folate (vitamin B₉), Cobalamin (vitamin B₁₂)

• Fat-Soluble Vitamins:

  • Vitamin A (retinol, β-carotenes)
  • Vitamin D (cholecalciferol)
  • Vitamin K (phylloquinones, menaquinones)
  • Vitamin E (tocopherols)

Vitamin C (Ascorbic Acid)

• Naturally Present: In some foods, added to others, and as a dietary supplement.
• Essential Dietary Component: Humans cannot synthesize vitamin C endogenously.
• Recommended Dietary Allowance (RDA): 90 mg/day for adult men, 75 mg/day for adult women.
• Functions:
  • Reducing agent (antioxidant)
  • Regeneration of vitamin E
  • Maintenance of connective tissue and wound healing (collagen).
  • Coenzyme in hydroxylation reactions.
• Deficiency:
  • Scurvy (sore and spongy gums, loss of teeth, fragile blood vessels, poor wound healing, frequent infections).
  • Microcytic anemia

Folic Acid (Vitamin B9)

• Sources: Leafy and dark green vegetables.
• Role in Metabolism: Key role in one-carbon metabolism (methyl, methylene, methenyl, formyl, or formimino) for DNA, polyamines, amino acids, creatine, and phospholipids synthesis.
• Deficiency: Likely the most common vitamin deficiency in the United States (particularly in pregnant women and those with alcoholism),
• Consequences: Megaloblastic anemia, Neural tube defects (supplementation recommended before conception and during the first trimester).
• Toxicity Issues: High-dose supplementation may be associated with an increased risk of cancer

Vitamin B12 (Cobalamin)

• RDA: 2.4 µg/day.
• Sources: Food from animal origin (liver, red meat, eggs, dairy products, fortified cereals).
• Synthesis: Synthesized only by microorganisms, not by plants.
• Function: Re-methylation of homocysteine to methionine, which requires N5-methyl THF. Deficiency results in elevated homocysteine levels.
• Deficiency: Pronounced in rapidly dividing cells (bone marrow and intestinal mucosal cells); megaloblastic anemia
• Clinical Significance: Related to neural tube defects.

Thiamine (Vitamin B1)

• Active Form: Thiamine pyrophosphate (TPP).
• Activation: Activated by transferring a pyrophosphate group from adenosine triphosphate (ATP).
• Coenzyme Role: Serves as a coenzyme in the oxidative decarboxylation of α-keto acids (important in Krebs' cycle)
• Energy Metabolism: Essential for energy metabolism (especially in the central nervous system).
• Deficiency: Decreased ATP production and impaired cellular function.

Riboflavin (Vitamin B2)

• Active Forms: Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
• Coenzyme Role: Tightly bound to flavoenzymes that catalyze oxidation or reduction of a substrate. Critically important for energy production.
• Stability: Stable to heat, but water-soluble, thus lost during food processing.
• RDA: Males 1.3 mg/day, Females 1.1 mg/day.
• Deficiency (Ariboflavinosis): Inflammation of membranes (mouth, skin, eyes, and GI tract)

Niacin (Vitamin B3)

• Alternative Names: Nicotinic acid or nicotinamide.
• Conversion: Nicotinamide in the diet can be converted into nicotinic acid in the body.
• Tryptophan Precursor: Dietary tryptophan is a precursor (1% of dietary protein).
• Active Forms: NAD (nicotinamide adenine dinucleotide) and NADP.
• RDA: Males 16 mg NE/day, Females 14 mg NE/day.
• Function: Important for metabolic reactions (Krebs' cycle).
• Deficiency (Pellagra): Diarrhea, dermatitis, dementia, and death (the "four Ds"). Primary pellagra from malnutrition (lack of niacin or tryptophan), secondary from impaired niacin absorption.

Pantothenic Acid (Vitamin B5)

• Adequate Intake: 5 mg/day for adults.
• Active Form: Coenzyme A (CoA).
• Function: Essential for energy metabolism, formation of acetyl CoA (Krebs' cycle), fatty acid synthesis, cholesterol synthesis, and ketone body synthesis.
• Sources: Moderate amounts in all nutrients; destroyed by food processing.
• Deficiency: Rare but can cause vomiting, hypoglycemia, and cramps.

Pyridoxal (Vitamin B6)

• Collective Term: Includes pyridoxine, pyridoxal, and pyridoxamine.
• Sources: Pyridoxine mainly in plants; pyridoxal and pyridoxamine primarily in animal foods.
• Active Form: Pyridoxal phosphate (PLP), serves as a coenzyme for many reactions involving amino acids (transamination, deamination, decarboxylation, condensation).
• RDA: 1.3 mg/day for adults
• Clinical Indications: Isoniazid use may lead to B6 deficiency. Therefore, dietary supplementation with B6 is often given as an adjunct to this treatment.
• Toxicity: Pyridoxine is the only water-soluble vitamin with significant toxicity, causing neurotoxicity (depression, fatigue, irritability, headaches, nerve damage, muscle weakness).

Biotin (Vitamin B7/H)

• RDA: 30 µg/day for adults.
• Enzyme Role: Coenzyme for decarboxylase enzyme in the TCA (Krebs' cycle) and gluconeogenesis
• Sources: Moderate amounts in most foods. Gut normal flora can produce biotin.
• Deficiency: rare but may cause depression, lethargy, or hair loss.

Test your knowledge on essential vitamins, including Vitamin C (ascorbic acid), B9 (Folic Acid), and B1 (Thiamine). This quiz covers recommended dietary allowances, deficiency symptoms, and primary functions of these vital nutrients. See how well you understand the importance of these vitamins in health.