Vitamins Study Notes

Chapter 6: Vitamins

The Nature of Vitamins

  • Role of Vitamins

    • Act as coenzymes: Vitamins often function as coenzymes in metabolic processes, enhancing the actions of enzymes.
    • Specific Functions: Each vitamin has distinct biochemical functions within the body that contribute to health.

  • Classification of Vitamins

    • Vitamins are classified based on their solubility into two main categories:
    • Fat-Soluble Vitamins: A, D, E, K
    • Water-Soluble Vitamins: C, and B complex vitamins (e.g., Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic acid, Biotin, Choline)

  • Dietary Reference Intakes (DRIs)

    • Recommended daily allowances including various measures:
    • International Units (IUs): Often used for vitamins A, D, and E.
    • Micrograms (mcg) and Milligrams (mg): Common units for measuring other vitamins.

Fat-Soluble Vitamins:

Vitamin A
  • Types: Includes preformed Vitamin A (retinol) and provitamin A carotenoids.
  • Absorption, Metabolism, and Excretion:
    • Key processes involve intestinal absorption and conversion into active forms, impacting vision, immune function, and skin health.
  • Functions: Vital for vision, skin health, and immune function.
  • Deficiency: Can result in night blindness and increased infection risk.
  • Sources: Found in liver, fish oils, milk, and brightly colored fruits and vegetables.
  • Toxicity: Can occur with excessive intake, leading to symptoms like headaches and liver damage.
Vitamin D
  • Absorption, Metabolism, and Excretion:
    • Synthesized in the skin via sunlight exposure (cholesterol + sunlight) and obtained from dietary sources.
    • Active forms include Vitamin D3 (cholecalciferol from animal sources) and Vitamin D2 (ergocalciferol from plant sources).
  • Functions: Crucial for calcium absorption, regulation of calcium and phosphorus levels in the blood, and bone mineralization.
  • Deficiency: Can lead to rickets in children and osteomalacia in adults.
  • Dietary Reference Intakes (DRIs) and Sources: Recommended intake varies; sources include fatty fish, fortified foods, and supplements.
  • Interfering Factors: Conditions like obesity and certain gut malabsorption disorders can affect vitamin D efficacy.
  • Toxicity: Rare but may cause hypercalcemia and related complications.
Vitamin E
  • Absorption, Metabolism, and Excretion:
    • Absorbed along with fats from the diet and stored in adipose tissue.
  • Functions: Acts mainly as an antioxidant, protecting cell membranes from oxidative damage.
  • Deficiency: May lead to neurological problems due to membrane damage.
  • Sources: Includes vegetable oils, nuts, and green leafy vegetables.
  • Stability and Interfering Factors: Sensitive to heat and light; can be lost through food processing.
  • Toxicity: Rare but could lead to an increased risk of bleeding.
Vitamin K
  • Absorption, Metabolism, and Excretion:
    • Absorbed in the intestine and stored in the liver.
  • Functions: Essential for blood clotting, bone metabolism, and regulating calcium levels in the blood.
  • Deficiency: Can lead to increased bleeding and bone weakness.
  • Sources: Found in green leafy vegetables, certain fruits, and bacterial synthesis in the gut.
  • Stability and Interfering Factors: Sensitive to heat; various medications can affect absorption.
  • Toxicity: Generally considered safe, but high doses can interfere with anticoagulant therapies.
Clicker Question on Vitamin K Functions
  • Functions of vitamin K include:
    • Bone formation
    • Epithelial tissue growth
    • Red blood cell formation
    • Blood Clotting (correct answer)

Water-Soluble Vitamins:

Vitamin C
  • Absorption, Metabolism, and Excretion:
    • Easily absorbed and not stored in large quantities; excess excreted via urine.
  • Functions: Important for collagen synthesis, immune function, and antioxidant protection.
  • Deficiency: Lead to scurvy characterized by bleeding gums and weakness.
  • Stability and Preservation: Sensitive to heat and light; often lost during food processing.
  • Increased Needs: Smokers and individuals under stress may require higher intake.
  • Food Processing Use: As an antioxidant in preserving food quality.
  • Toxicity: High doses can cause gastrointestinal disturbances.
B-Complex Vitamins:
Thiamin (Vitamin B1)
  • Absorption, Metabolism, and Excretion:
    • Well absorbed through the small intestine; excess is excreted via urine.
  • Functions: Essential for carbohydrate metabolism and nerve function.
  • Deficiency: Can lead to Beriberi, affecting the cardiovascular and nervous system.
  • Stability and Interfering Factors: Sensitive to heat and sulfites; cooking can reduce levels.
  • Toxicity: Generally non-toxic; excess is excreted.
Riboflavin (Vitamin B2)
  • Absorption, Metabolism, and Excretion:
    • Absorbed through the intestine and utilized in energy metabolism.
  • Functions and Pharmaceutical Potential: Involved in redox reactions and may help with migraines.
  • Deficiency: Results in sore throat, cracks on the outsides of the lips, and inflammation.
  • Stability and Interfering Factors: Sensitive to light.
  • Toxicity: Considered safe with no established toxic level.
Niacin (Vitamin B3)
  • Absorption, Metabolism, and Excretion:
    • Absorbed in the small intestine and metabolized in the liver.
  • Function: Contributes to energy production and DNA repair.
  • Deficiency: Can lead to Pellagra, characterized by dermatitis, diarrhea, and dementia.
  • Sources and Stability: Found in meat, fish, and grains; stable in heat.
  • Toxicity: High doses may cause flushing and liver damage.
Vitamin B6 (Pyridoxine)
  • Absorption, Metabolism, and Excretion:
    • Absorbed from the intestine; involved in amino acid metabolism.
  • Functions: Important for neurotransmitter synthesis and red blood cell formation.
  • Deficiency: Can result in anemia, irritability, and peripheral neuropathy.
  • Sources and Stability: Contains whole grains, fish, and potatoes; heat-stable.
  • Toxicity: Excess can lead to neuropathy and sensory loss.
Folate (Vitamin B9)
  • Absorption, Metabolism, and Excretion:
    • Absorbed in the upper intestine; vital for DNA and RNA synthesis.
  • Functions: Crucial for cell division and DNA synthesis.
  • Deficiency: Can cause anemia and neural tube defects in pregnancy.
  • Dietary Reference Intakes (DRIs): Varies based on age and life stage, particularly for pregnant women.
  • Sources and Stability: Dark leafy greens, legumes, and fortified grains; sensitive to heat and light.
  • Interfering Factors: Alcohol can inhibit absorption.
  • Toxicity: High intakes may mask B12 deficiency.
Vitamin B12 (Cobalamin)
  • Absorption, Metabolism, and Excretion:
    • Requires intrinsic factor for absorption in the ileum.
  • Functions: Important for DNA synthesis and neurological function.
  • Sources: Predominantly found in animal products; fortified cereals for vegans.
  • Deficiency: Can lead to pernicious anemia and neurological issues.
  • Interfering Factors: Vegan diet and certain gastrointestinal conditions may affect absorption.
  • Toxicity: Generally considered safe; no known toxicity.
Other Essential Nutrients
  • Pantothenic Acid: Part of coenzyme A; deficiency is rare but can lead to fatigue and irritability.
  • Biotin: Coenzyme in energy metabolism; deficiency may lead to hair loss and skin issues.
  • Choline: Important for neurotransmitter synthesis; excessive intake has implications for cardiovascular health.

Vitamin Supplements

  • Guidelines for Use:
    • Supplements are not substitutes for a healthy diet; no groups promote regular use of multivitamins without considering diet quality.
    • Intake should not exceed 100% of the recommended dietary allowance/adequate intakes (RDA/AIs).
Clicker Question Regarding Vitamin C Deficiency
  • An individual with a vitamin C deficiency may develop:
    • Fat absorption problems
    • Scurvy (correct answer)
    • Beriberi
    • Night blindness
Answer to Vitamin C Deficiency
  • The correct answer is B: Signs of scurvy can appear within 1 month of vitamin C intake of less than 10 milligrams per day (National Institutes of Health, February 11, 2016).
  • Fat absorption problems signal vitamin K deficiency.
  • Beriberi is related to thiamin deficiency.
  • Night blindness is caused by vitamin A deficiency, leading to xerophthalmia.