• Forms, properties, sources, functions, effects of deficiencies and Recommended Daily Allowances (RDAs)/Reference Intakes (RIs) of fat-soluble and water-soluble vitamins
Vitamins are one of the micronutrients. The human body synthesises few vitamins: they must be obtained from food or manufactured supplements. Each vitamin has its own specific functions. Insufficient amounts of vitamins in the diet may cause deficiency diseases.
Classification of vitamins Fat-soluble vitamins
• Normally found in food that contains fat • Can be stored in the body for several months
Vitamin A: retinol and beta-carotene Vitamin D: cholcalciferol and ergocalciferol Vitamin E: tocopherol Vitamin K: naphthoquinones
Water-soluble vitamins
• Found in a wide variety of food • Not stored in the body (excess are excreted)
Vitamin C: ascorbic acid B group vitamins: B1 thiamine
B6 pyrodoxine
B2 riboflavin B12 cobalamin B3 niacin
FAT-SOLUBLE VITAMINS Vitamin A (retinol and beta-carotene)
Forms • Retinol (pure vitamin A): easily absorbed. Stored in the liver.
HL
Properties of retinol (pure vitamin A)
• A yellow, fat-soluble alcohol • Insoluble in water • Soluble in organic solvents, e.g. acetone
• Heat stable, but affected by prolonged high temperatures
• Destroyed by oxygen
• Beta-carotene (pro-vitamin A): not easily absorbed. Converted to retinol in the lining of the intestine.
Properties of beta-carotene (pro-vitamin A)
• A yellow or orange fat-soluble oil • Insoluble in water • Soluble in fat solvents, e.g. alcohol • Heat stable, but affected by prolonged high temperatures • Unaffected by oxygen • A powerful antioxidant that has the ability to counteract the damaging effects of free radicals (chemicals that can damage the human body)
