Chapter 9 THE FAT-SOLUBLE VITAMINS

Fat-Soluble Vitamins Vitamins A, D, E and K are fat-soluble vitamins. Fat-soluble vitamins require bile and dietary fat for absorption. Once absorbed, they are transported with fats through the lymphatic system in chylomicrons before entering the blood. Fat-soluble vitamins can be stored in body fat, meaning that intakes can vary without a risk of deficiency (as long as there are average intakes over time). Because they can be stored in body fat, fat-soluble vitamins are not easily excreted. This increases the risk of toxicity with high intakes. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin A Vitamin A is found preformed, from animal products or supplements, or in precursor form, from plant foods, in the diet. Vitamin A plays a key role in night vision, cell differentiation and growth regulation. Preformed vitamin A compounds are known as retinoids. Plants contain precursors to vitamin A known as carotenoids. A derivative of retinoic acid is used topically to treat certain skin conditions. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin A in the Diet Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin A and the Visual Cycle Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin A and Gene Expression Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin A Deficiency and Toxicity Vitamin A deficiency is a threat to the health, sight and lives of millions of children around the world. Vitamin A deficiency can be caused by insufficient intake of vitamin A, fat, protein or zinc. Preformed vitamin A can be toxic if taken in high amounts. Medications made from vitamin A, such as Retin A or Accutane, can cause serious side effects. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin D Vitamin D is known as the “sunshine vitamin” because it can be produced in the skin by exposure to UV light. Only a few foods are natural sources of Vitamin D, including liver, fatty fish, fish oils and egg yolks. Vitamin D can be toxic at high levels, so there are strict limitations on the categories of foods that can be vitamin D-fortified. Vitamin D is important for bone health, normal functioning of the parathyroid gland and regulation of the immune system. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin D in the Diet Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin D from UV Light or the Diet Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin D Deficiency and Toxicity When vitamin D is deficient, dietary calcium cannot be absorbed efficiently and there can be improper bone mineralization and abnormalities in bone structure. In children, vitamin D deficiency can result in rickets; in adults, osteomalacia. 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. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin E Vitamin E is also called tocopherol. Vitamin E has antioxidant properties. Alpha-tocopherol is the form of vitamin E absorbed by the human body. Vitamin E absorption depends on normal fat absorption. Once absorbed, vitamin E is incorporated into chylomicrons. Vitamin E deficiency in newborns might result in hemolytic anemia. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin E in the Diet Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin E is an Antioxidant Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin K Vitamin K was named for koagulation, the Danish word for coagulation. Vitamin K is found in several forms, including phylloquinone and menaquinones. Abnormal blood coagulation is the major symptom of vitamin K deficiency. Vitamin K deficiency is very rare in the US. Copyright 2012, John Wiley & Sons Canada, Ltd.

Vitamin K in the Diet Copyright 2012, John Wiley & Sons Canada, Ltd.

A Summary of the Fat-Soluble Vitamins Copyright 2012, John Wiley & Sons Canada, Ltd.

A Summary of the Fat-Soluble Vitamins Copyright 2012, John Wiley & Sons Canada, Ltd.

Benefits and Risks of Fat-Soluble Vitamin Supplements Copyright 2012, John Wiley & Sons Canada, Ltd.

Label Literacy About 40% of Canadian adults use vitamin and mineral supplements. You can purchase almost any nutrient as an individual supplement or you can choose from a number of combinations of nutrients, herbs and other components. Health Canada regulates minimum and maximum doses of vitamins and minerals that are permitted in a supplement. The maximum allowable dose is usually the UL. Copyright 2012, John Wiley & Sons Canada, Ltd.

Label Literacy (continued) The information included on supplement labels can be used to determine if a supplement includes the nutrients you want and whether they are present in appropriate amounts. Supplements can be part of an effective strategy to promote good health, but they should never be considered a substitute for other good health habits and should never be used instead of medical therapy. Copyright 2012, John Wiley & Sons Canada, Ltd.

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