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Chapter 9The Fat-Soluble Vitamins

Fat-Soluble Vitaminsn Vitamins A, D, E and K n Require bile and dietary fat for absorptionn Once absorbed, they are transported with fats

through the lymphatic system in chylomicronsbefore entering the blood

n Can be stored in body fat so intakes can vary without a risk of deficiency (as long as there are average intakes over time)

n Because they can be stored in body fat, fat-soluble vitamins are not easily excretedq This increases the risk of toxicity with high intakes

Vitamin An Found preformed, from animal products or

supplements, or in precursor form, from plant foods, in the dietq Preformed vitamin A compounds are known as retinoids

q Plants contain precursors to vitamin A known as carotenoids

n Plays a key role in night vision, cell differentiation and growth regulation

n A derivative of retinoic acid is used topically to treat certain skin conditions

Vitamin A: Dietary Sources

Forms of Vitamin A

Vitamin A and the Visual Cycle

Vitamin A and Gene Expression

Vitamin A and Keratin

Vitamin A Deficiency and Toxicityn Vitamin A deficiency can cause night

blindness as well as permanent blindnessn Vitamin A deficiency can be caused by

insufficient intake of vitamin A, fat, protein or zinc

n Preformed vitamin A can be toxic if taken in high amounts

n Medications made from vitamin A, such as Retin-A or Accutane, can cause serious side effects

Vitamin A Hypercarotenemia

Vitamin D (Cholecalciferol)n The “sunshine vitamin”

q Can be produced in the skin by exposure to UV light

n Toxic at high levels, so there are strict limitations on the categories of foods that can be fortified with vitamin D

n Important for bone health, normal functioning of the parathyroid gland and regulation of the immune system

Vitamin D: Dietary Sources

Vitamin D: Synthesis and Activation

Vitamin D and Calcium Absorption

Vitamin D: Deficiency and Toxicityn When vitamin D is deficient, dietary calcium

cannot be absorbed efficiently and there can be improper bone mineralization and abnormalities in bone structure

n Rickets—vitamin D deficiency in childrenn Osteomalacia—vitamin D deficiency in adultsn Oversupplementation of vitamin D can result in

high blood and urine calcium concentrations, depositing of calcium in blood vessels and kidneys, cardiovascular damage and possibly death

Vitamin D Deficiency

Vitamin E (Tocopherol)n Vitamin E has antioxidant propertiesn Alpha-tocopherol—the form of vitamin E

absorbed by the human bodyn Absorption depends on normal fat

absorptionq Once absorbed, vitamin E is incorporated into

chylomicronsn Vitamin E deficiency in newborns might

result in hemolytic anemia

Vitamin E: Dietary Sources

The Antioxidant Function of Vitamin E

Vitamin Kn Named for koagulation, the Danish word

for coagulationn Phylloquinone—vitamin K in plantsn Menaquinones—form of vitamin K found

in fish oil and meats, and synthesized by bacteria

n Abnormal blood coagulation is the major symptom of vitamin K deficiency

n Vitamin K deficiency is very rare in the U.S.

Vitamin K: Dietary Sources

Vitamin K and Blood Clotting

Benefits and Risks of Fat-Soluble Vitamin Supplements

Who Needs Supplementation?

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