Vitamins are organic substances found in minute quantities in food that are essential for metabolism. Both fat-soluble (which dissolve in fat and thus can be stored by the body) and water-soluble (which dissolve in water and thus cannot be stored by the body) vitamins play a variety of physiologic roles in the body. Vitamin concentrations in blood, urine, and certain body tissues can be measured and reflect the nutritional status of the patient.

Vitamins have varying modes of action. For instance, vitamin E is an antioxidant, vitamin C is an enzyme cofactor, and vitamin A is an anti-infection agent.

Sources of fat-soluble vitamins include dietary substances and biologic or intestinal microorganisms. Fat-soluble vitamins include vitamin A (retinol or carotene), vitamin D (calciferol), vitamin E (tocopherol), and vitamin K (consisting of phylloquinones or K₁, menaquinones or K₂, and menadiones or K₃).

The sources of water-soluble vitamins are dietary substances and intestinal microorganisms. Water-soluble vitamins include vitamin C (ascorbic acid) and the B-complex vitamins, such as biotin, vitamin B₁₂ (cobalamin), folate (folic acid), vitamin B₃ (niacin), vitamin B₆ (pyridoxine), vitamin B₂ (riboflavin), vitamin B₁ (thiamine), and pantothenic acid.

These tests are measurements of nutritional status. Low levels indicate recent inadequate oral intake, poor nutritional status, or malabsorption problems. They may not reflect tissue stores. High levels indicate excessive intake, intoxication, or absorption problems.

Subtopic(s):

• Reference Values
• Procedure
• Clinical Implications
• Interfering Factors
• Interventions