3.1 Vitamins: Fat-soluble and water-soluble vitamins, functions, and deficiencies

Vitamins are essential micronutrients our bodies need to function properly. They're split into two groups: fat-soluble (A, D, E, K) and water-soluble (B-complex and C). Each type has unique characteristics in how they're absorbed, stored, and used by our bodies.

Fat-soluble vitamins can be stored in our body fat, while water-soluble ones are used quickly or flushed out. Both types play crucial roles in health, from supporting vision and bone strength to boosting our immune system and helping our bodies make energy from food.

Fat-soluble vs Water-soluble Vitamins

Absorption and Transport

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• Fat-soluble vitamins (A, D, E, and K) are absorbed along with dietary fats in the small intestine require bile acids for absorption
  • Transported in the lymphatic system and bloodstream by lipoproteins
• Water-soluble vitamins (B-complex and C) are absorbed directly into the bloodstream from the small intestine do not require bile acids for absorption

Storage and Excretion

• Fat-soluble vitamins can be stored in the liver and adipose tissue for extended periods excess amounts can lead to toxicity
• Water-soluble vitamins are not stored in significant amounts in the body excess amounts are excreted in the urine making toxicity less common than with fat-soluble vitamins

Vitamin Functions for Health

Vision, Immune Function, and Cell Health

• Vitamin A (retinol) plays a crucial role in:
  • Vision
  • Immune function
  • Cell differentiation
  • Maintaining healthy skin and mucous membranes
• Vitamin E (tocopherol):
  • Potent antioxidant that protects cell membranes from oxidative damage
  • Supports immune function

Bone Health, Blood Clotting, and Metabolism

• Vitamin D (calciferol) is essential for:
  • Calcium and phosphorus absorption
  • Bone health
  • Immune function
  • Can be synthesized in the skin upon exposure to sunlight
• Vitamin K (phylloquinone and menaquinone) is necessary for:
  • Blood clotting
  • Bone metabolism
• B-complex vitamins (thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, vitamin B12, and folate) have various roles in:
  • Energy metabolism
  • Nervous system function
  • Red blood cell formation
  • DNA synthesis
• Vitamin C (ascorbic acid):
  • Powerful antioxidant that supports collagen synthesis
  • Supports immune function and iron absorption

Vitamin Deficiencies and Toxicities

Fat-soluble Vitamin Deficiencies and Toxicities

• Vitamin A deficiency can lead to:
  • Night blindness
  • Xerophthalmia (dry eyes)
  • Increased susceptibility to infections
• Vitamin A toxicity can cause:
  • Liver damage
  • Birth defects
  • Bone abnormalities
• Vitamin D deficiency results in:
  • Rickets in children
  • Osteomalacia in adults
• Vitamin D toxicity can cause:
  • Hypercalcemia (high blood calcium)
  • Kidney stones
  • Calcification of soft tissues
• Vitamin E deficiency is rare but may cause:
  • Neurological problems
  • Hemolytic anemia in premature infants
• Vitamin E toxicity is uncommon but can interfere with vitamin K metabolism and blood clotting
• Vitamin K deficiency can lead to bleeding disorders while toxicity is rare due to its low potential for accumulation

Water-soluble Vitamin Deficiencies and Toxicities

• B-vitamin deficiencies can cause various disorders:
  • Beriberi (thiamin deficiency)
  • Ariboflavinosis (riboflavin deficiency)
  • Pellagra (niacin deficiency)
  • Megaloblastic anemia (vitamin B12 and folate deficiency)
• B-vitamin toxicities are rare due to their water-soluble nature
• Vitamin C deficiency causes scurvy characterized by:
  • Connective tissue weakness
  • Poor wound healing
  • Bleeding gums
• Vitamin C toxicity is rare but may cause gastrointestinal distress and kidney stones in high doses

Vitamin Interactions and Bioavailability

Nutrient Interactions and Absorption

• Fat-soluble vitamins require dietary fat and bile acids for optimal absorption while water-soluble vitamins are absorbed more readily
• Vitamin D enhances calcium and phosphorus absorption while vitamin C improves non-heme iron absorption
• Vitamin E and vitamin C work synergistically as antioxidants to protect cells from oxidative stress
• Vitamin B12 absorption depends on the presence of intrinsic factor a protein secreted by the stomach

Factors Affecting Bioavailability and Utilization

• Folate bioavailability is affected by food processing and cooking methods with synthetic folic acid being more bioavailable than naturally occurring folate
• Certain medications such as orlistat (a weight-loss drug) can interfere with the absorption of fat-soluble vitamins
• Genetic variations can influence vitamin metabolism and requirements such as the MTHFR gene variant affecting folate metabolism