Interactive Summaries

Chapter 10: Fat-Soluble Vitamins

Vitamin A

The body uses active forms of vitamin A, known collectively as the . While all three forms have essential functions, is the key player in the vitamin A family. In well-nourished people, the stores more than (90%) of the body's vitamin A. The remainder is stored in adipose tissue, lungs, and kidneys. Vitamin A is important to vision. In the eye, retinal combines with opsin to form a pigment called which makes it possible to see in dim light. Vitamin A is also involved in color vision as part of the pigment in . A lack of vitamin A effects rod cells first so as a vitamin A deficiency worsens emerges before . A large proportion of the body’s vitamin A is in the form of retinoic acid. It is involved in cell differentiation, the process when develop into specific types of cells with unique functions.

The best sources of provitamin A carotenoids are dark green and vegetables. Ten percent of the vitamin A content in animal foods is in the form of retinol and the remaining 90% is . Vitamin A deficiency is the leading cause of in the world.

Vitamin D

The body can synthesize all of the vitamin D it needs with just sufficient amounts of . Vitamin D is considered both a vitamin and a . Adequate vitamin D prevents a childhood disease called . The liver and adipose tissue store vitamin D. When it is needed the liver and kidneys convert stored vitamin D to , which works with parathyroid hormone and from the thyroid gland to regulate blood calcium levels. When blood calcium levels are too high calcitonin inhibits the activity of and shifts the balance towards the activity of the osteoblasts. This activity removes calcium ions from the bloodstream and deposits them in new bone. Infants are born with stores of vitamin D that last up to . Adults can get an adequate supply of vitamin D as long as they expose their face, hands, and arms to the sun about 1/3 to 1/2 the time it would take you to burn . Other than fortified products, good amounts of vitamin D can also be found in . In the United States, rickets is sometimes seen in children who have fat malabsorption syndromes such as . is a related skeletal problem seen in adults with a vitamin D deficiency that results in softened bones and bending of the spine.

Vitamin E

Unlike vitamins A and D, vitamin E . Adipose tissue stores 90 percent of the body’s vitamin E and the rest can be found in . Vitamin E is an antioxidant that it is enhanced by and selenium. Your body normally creates some free radicals to control unwanted molecules. If the body fails to control them, these free radicals will start to damage healthy cells, leading to chronic diseases such as . To prevent vitamin E deficiency, the intake requirement is related to body size and intake. contains the highest concentration of usable vitamin E. Much of the vitamin E in oils is destroyed during processing by oxidation. Vitamin E is usually transferred from mother to fetus in the last weeks of pregnancy. If a baby is born prematurely and does not have adequate vitamin E stores, the baby may develop which occurs after oxidation causes red blood cells to burst.

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