Interactive Summaries

Chapter 9: Vitamins: Vital Keys to Health

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. Vitamin A deficiency is the leading cause of in the world.

Vitamin C

Vitamin C plays an important role in the formation of the most abundant protein in the human body . Like vitamin E, Vitamin C works as an . Vitamin C is needed to synthesize . The first signs of scurvy arise after of a vitamin C free diet. Scurvy is in developed countries. Less severe signs of inadequate vitamin C intake are .

If a healthy person consumes more than of vitamin C a day for a prolonged period of time this may lead to nausea, abdominal cramps, and nosebleeds. Vitamin C has been reputed to prevent or cure .

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. 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 . is a related skeletal problem seen in adults with a vitamin D deficiency that results in softened bones and bending of the spine.

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