U01.01.061 Vitamins: fat soluble

Fat-soluble vitamins (A, D, E, and K) are absorbed and transported through the body in a manner distinct from water-soluble vitamins. Their absorption and utilization heavily depend on the function of the ileum and the pancreas.

Key Points:

Absorption: Fat-soluble vitamins require dietary fat for absorption in the small intestine, specifically the ileum. They are transported in the bloodstream via lipoproteins.
Storage: These vitamins are stored in fat tissue and the liver, which contributes to a higher risk of toxicity due to accumulation.
Toxicity: Fat-soluble vitamin toxicity is more common than water-soluble vitamin toxicity. This is because excess fat-soluble vitamins are not easily excreted and can accumulate in the body.

Deficiency Risk Factors:

Certain conditions can impair fat-soluble vitamin absorption and lead to deficiencies, such as:

Malabsorption Syndromes:
- Cystic fibrosis
- Celiac disease
Other Risk Factors:
- Mineral oil intake (which interferes with fat absorption)

Table: Fat-Soluble Vitamins and Absorption

Vitamin	Role in the Body	Absorption Site	Toxicity Symptoms	Deficiency Risk Factors
Vitamin A	Vision, immune function, skin health	Ileum	Nausea, dizziness, liver damage	Cystic fibrosis, mineral oil intake
Vitamin D	Calcium and phosphate metabolism, bone health	Ileum	Hypercalcemia, kidney stones	Cystic fibrosis, celiac disease
Vitamin E	Antioxidant protects cell membranes	Small intestine	Hemolysis, muscle weakness	Malabsorption syndromes, mineral oil
Vitamin K	Blood clotting, bone health	Small intestine	Bleeding, bruising	Celiac disease, cystic fibrosis

Points to Remember:

Absorption of Fat-Soluble Vitamins: Dependent on pancreatic enzymes and the ileum.
Deficiency Risks: Conditions such as cystic fibrosis, celiac disease, and mineral oil intake impair absorption.
Toxicity: Fat-soluble vitamins are stored in fat, making them more prone to toxicity compared to water-soluble vitamins.
Malabsorption Syndromes: Lead to deficiencies in fat-soluble vitamins due to impaired absorption of dietary fat.

USMLE Step 1 Review Series

Curriculum

U01.01.061 Vitamins: fat soluble

Key Points:

Deficiency Risk Factors:

Table: Fat-Soluble Vitamins and Absorption

Points to Remember:

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