Nutrition & Diet Chapter 8 - Vitamins

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retinoids or preformed vitamin A

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-found in animal foods (such as fish and organ meats)

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-carotenoids

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-plant sources
-carotenoids are converted into provitamin A (converted into vitamin A as needed)
-include beta-carotene (orange-yellow pigment in carrots), lutein and zeaxanthin

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Functions of Vitamin A

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Promote Night and Color Vision

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Promote Night and Color Vision

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-allows cells in the eye to adjust from bright to dim light (such as seeing the headlights of
an oncoming car

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night blindness

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-retina is unable to adjust to low levels of light

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xerophthalmia

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-cells that line the cornea lose the ability to produce mucus
-“dry eye”
-increases the risk of abrasion from surface dirt/dust and bacterial infection

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vitamin A deficiency is generally a problem in

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children in less developed nations

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macular degeneration

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associated with changes in the macular area of the eye
(provides detailed vision)
-age, smoking and genetics are risk factors
-carotenoids in the diet may lower the risk of age related macular degeneration and may reduce the risk of cataracts

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epithelial cells

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line or cover body surfaces
-skin
-lining of body systems including respiratory, digestive and urinary
-important barriers to prevent bacterial infection
-some epithelial cells secrete mucus that serves as a lubricant

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decrease in vitamin A results in

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decrease in mucus production which can increase
infection rates

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vitamin A is referred to as

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the “anti-infection” vitamin

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vitamin A thus effects gene expression

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use of DNA information on a gene to produce a protein

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carotenoids

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may help prevent cancers
-act as antioxidants
-decrease the risk of oral and lung cancer
-lycopene, a dietary carotenoid, may decrease skin cancer risk and may protect
against prostate cancer
-found in watermelon and tomatoes

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-most researchers are convinced that beta-carotene supplementation offers

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no protection against cancer

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-Retin-A

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-topical treatment for acne

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analog form of vitamin A

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-analog is a chemical compound that differs slightly from another
compound

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Accutane

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-oral drug for the treatment of serious acne
-acts to regulate development of cells in the skin
-contraindicated during pregnancy
-induces toxic symptoms and can cause birth defects in offspring

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-preformed vitamin A sources

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-liver and fish oils
-vitamin A fortified milk, breakfast cereals and margarines

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-provitamin A carotenoids

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-dark green and yellow-orange vegetables and some fruits
-carrots, winter squash and sweet potatoes (yellow-orange)
-spinach and broccoli (dark green)
-peaches, cantaloupe and apricots

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deficiencies of vitamin A may be noted within the following groups

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-preschool children who do not consume enough vegetables
-individuals with alcoholism or liver disease (limits vitamin A storage)
-individuals with severe fat-malabsorption
-elderly individuals and the urban poor

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skin cells produce prohormone vitamin D

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when exposed to UVB rays from the sun

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the liver and kidney convert prohormone vitamin D into

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its active hormone form (1,25-
dihydroxyvitamin D)

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UVB exposure provides

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80% to 100% of our vitamin D needs

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1,25-dihydroxyvitamin D

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-helps regulate the absorption of calcium and phosphorus from the intestine
-is also involved in the deposition of calcium in the bones

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calcitonin

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-produced by the thyroid gland
-promotes the removal of calcium from the blood into the bone
-lowers blood calcium levels

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parathyroid hormone

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-produced by the parathyroid gland
-promotes the removal of calcium from the bone into the blood
-increases blood calcium levels

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rickets

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-infants and children
-bones weaken and bow due to softening of the bones
-recent studies have shown rickets to be a problem in breast-fed infants with
little sun exposure
-prevention (under physician’s guidance) involves supplemental vitamin D
-rickets is also a problem in children with poor fat absorption
-cystic fibrosis (pancreatic ducts are blocked and enzymes are not released)

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-osteomalacia

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-adults
-means “soft bones”
-caused by inefficient calcium absorption in the small intestine or poor
conservation of calcium by the kidneys
-calcium is removed from bone to replace deficiencies in the diet
-bones become porous and weak and easily fracture

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Sources of Vitamin D

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-fatty fish (ex. sardines and salmon)
-fortified milk, yogurt and breakfast cereals