chapter 8
what is retinal?
Aldehyde form of vitamin A.
what is a vitamin?
An essential organic (carbon-containing) compound needed in small amounts in the diet to help regulate and support chemical reactions and processes in the body.
_______, the orange-yellow pigment in carrots, is the only carotenoid that can be sufficiently absorbed and converted into _______ to play a significant role as a source of vitamin A and as a powerful antioxidant.
Beta-carotene, retinol
what is 1,25-dihydroxyvitamin D3 (calcitriol)
Biologically active form of vitamin D
Xerophthalmia can progress to the stage where there is an accumulation of dead cells and secretions on the surface of the eye. This condition is called
Bitot's spots
_______ are phytochemicals, that is, chemicals within plants that have health-promoting properties for humans.
Carotenoids
_______ by themselves may play a role in preventing cancer, as a by-product of their antioxidant activity. Population studies show that regular consumption of foods rich in ________ decreases the risk of ____
Carotenoids (x2) lung and oral cancers.
what are retinoids?
Chemical forms of preformed vitamin A; one source is animal foods.
what is xerophthalmia
Hardening of the cornea and drying of the surface of the eye, which can result in blindness.
Vitamin D regulates blood calcium in three ways:
(1) it influences the absorption of calcium and phosphorus from the small intestine; (2) in combination with PTH and calcitonin, it regulates calcium excretion via the kidney; and (3) it affects the deposition or withdrawal of minerals from the bones
To be classified as a vitamin, a compound must meet the following criteria:
(1) the body is unable to synthesize enough of the compound to maintain health and (2) absence of the compound from the diet for a defined period produces deficiency symptoms that, if caught in time, are quickly cured when the compound is resupplied.
Dietary carotenoids do not produce toxic effects because
(1) their rate of conversion into vitamin A is relatively slow and regulated and (2) the efficiency of carotenoid absorption from the small intestine decreases markedly as oral intake increases.
The human production of vitamin D begins when the ultraviolet B (UVB) rays of the sun convert a cholesterol precursor of vitamin D ____ found in the skin into an inactive form of vitamin D ____. This compound must be activated to ________ in the liver and to ______ in the kidney before it can function as the vitamin D hormone.
(7-dehydrocholesterol) (cholecalciferol) 25-hydroxyvitamin D3 (calcidiol) 1,25-dihydroxyvitamin D3 (calcitriol)
what is retinoic acid
Acid form of vitamin A.
what is Osteomalacia
Adult form of rickets. The bones have low mineral density and subsequently are at risk for fracture.
Dark skin pigmentation, geographic latitude, time of day, season of the year, weather conditions, and amount of body surface covered with clothing or sunscreen affect the skin's exposure to ___ and therefore influence
UVB rays vitamin D synthesis.
vitamins in vegetables
Vitamin A Vitamin K Folate Vitamin C
vitamins in fruits
Vitamin A and Vitamin C
what is night blindness
Vitamin A-deficiency disorder that results in loss of the ability to see under low-light conditions.
what is a megadose?
Intake of a nutrient beyond estimates of needs to prevent a deficiency or what would be found in a balanced diet; 2 to 10 times human needs is a starting point for such a dosage.
It can result from inadequate calcium intake, inefficient calcium absorption in the intestine, or poor conservation of calcium by the kidneys. It occurs most commonly in people with kidney, stomach, gallbladder, or intestinal disease (especially when most of the intestine has been removed) and in people with cirrhosis of the liver. what disease is this?
Osteomalacia
what is 7-dehydrocholesterol
Precursor of vitamin D found in the skin.
what are carotenoids
Precursors of vitamin A found in plant foods.
what is vitamin D3 (cholecalciferol)
Previtamin form found naturally in some animal sources, including fish and egg yolks.
What is bioavailability?
The degree to which an ingested nutrient is digested and absorbed and thus is available to the body.
what is a fetus?.
The developing human life form from 8 weeks after conception until birth.
what is tissue saturation?
The limited storage capacity of water-soluble vitamins in the tissues.
what is scurvy?
The vitamin C-deficiency disease characterized by weakness, fatigue, slow wound healing, opening of previously healed wounds, bone pain, fractures, sore and bleeding gums, diarrhea, and pinpoint hemorrhages on the skin.
Water-soluble vitamins are handled much differently than fat-soluble vitamins. After being ingested, the B vitamins from food are first broken down from their active ______ forms into free vitamins in the stomach and small intestine. The vitamins are then absorbed, primarily in the _______-
coenzyme, small intestine
Food cooperatives, ____________, and farmers' markets are great sources of freshly harvested fruits and vegetables.
community-supported agriculture (CSA)
Without vitamin A, mucus-forming cells, such as those in the intestines and lungs, do what? For the eye, this can lead to ____
deteriorate and lose function. blindness
The fat-soluble vitamins (A, D, E, and K) are absorbed along with _____. These vitamins then travel with dietary fats as part of ______ through the bloodstream to reach body cells.
dietary fat, chylomicrons
These vitamins can build up to toxic levels in the body if you consume too many of them, because it is hard for your body to excrete them. what vitamin is this>
fat-soluble vitamins
______ are not readily excreted, so some can easily accumulate in the body and cause toxic effects.
fat-soluble vitamins
Vitamin A fights infection by
helping the cells produce protective mucus in the eyes and in the intestinal tract and other epithelial cells
Water-soluble vitamins are transported to the liver via the _______ and are distributed to body tissues. Once inside cells, the active coenzyme forms are _____
hepatic portal vein, resynthesized
A high carotenoid concentration in the blood (called ________) can occur if someone routinely consumes large amounts of carrots or takes pills containing beta-carotene (more than 30 milligrams daily) or if infants eat a great deal of squash. The skin turns _____, particularly the palms of the hands and soles of the feet.
hypercarotenemia yellow-orange
During early fetal growth, vitamin A functions in the differentiation and maturation of cells, which ultimately forms
tissue and organs
For most water-soluble vitamins, when you consume more than the RDA or AI, the kidneys efficiently filter the excess from the blood and excrete these compounds in ____-
urine
Almost all (90%) of ______ is stored in the liver; the remaining 10% is in adipose tissue, kidneys, and the lungs.
vitamin A
At the genetic level, _______-- binds to receptors on DNA to increase synthesis of a variety of proteins. Some of these proteins are required for growth
vitamin A
There are two forms of vitamin D:
vitamin D2 and vitamin D3.
Vitamins can be divided into two broad classes based on solubility:
vitamins A, D, E, and K are fat-soluble vitamins, whereas the B vitamins and vitamin C are water-soluble vitamins.
your body cannot easily store most of the ten _______. Your body can, however, excrete most excess _______ to avoid toxic buildups.
water-soluble vitamins (x2)
If vitamin A deficiency progresses, the cells that line the cornea of the eye (the clear window of the eye) lose the ability to produce mucus. The eye then becomes dry. This disease is called _______, which means dry eye.
xerophthalmia
Carotenoids are found in
yellow-orange and dark green vegetables and some fruits; food sources include spinach, carrots, sweet potatoes, and apricots.
The RDA for vitamin A (see margin) is expressed in________. These units consider the activity of both _______ that are synthesized into vitamin A in humans
retinol activity equivalents (RAE). preformed vitamin A and the carotenoids
There are three active forms of vitamin A:
retinol, retinal, and retinoic acid.
When retinol is stored, it is esterified (joined to a fatty acid) and becomes
retinyl
Vitamin D deficiency can occur at any time, but when it occurs during infancy and early childhood, the resulting disease is known as
rickets
Excretion of vitamins varies primarily on their
solubility
What is the best source of vitamin D?
sunlight
Vitamin D2 (ergocalciferol) is a
synthetic product derived from the irradiation of plant sterols (ergosterol) and is used in some supplements.
what is retinol?
the alcohol form of vitamin A
Vitamin D3 (cholecalciferol)—
the form synthesized in the human body—is more commonly used in supplements and fortified foods.
Fat-soluble vitamins are stored mostly in
the liver and fatty tissues.
vitamins in protein
thiamin riboflavin niacin biotin vitamin B-6 vitamin B-12 choline
vitamins in grains
thiamin, riboflavin, niacin, folic acid
The B vitamins include
thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, folate, and vitamin B-12.
what is 25-hydroxyvitamin D3 (calcidiol or calcifediol)
Form found in blood. Sometimes shortened to 25 (OH)D3.
what is vitamin D2 (ergocalciferol)
Form found in nonanimal sources, such as in some mushrooms.
___________ are effective ways to add vitamin D to your diet.
Fortified foods and supplements
During the early months of pregnancy, a high intake of preformed vitamin A is especially dangerous because it may cause fetal malformations and spontaneous abortions. why is this?
because vitamin A binds to DNA and thus influences cell development.
Typically, about 50% to 90% of the water-soluble vitamins in the diet are absorbed, which means they have relatively high ________.
bioavailability
Rods detect _____, and are responsible for night vision. Cones are responsible for ______. Rods and cones require _____ for normal function.
black and white, night vision color vision vitamin A
Vitamin A deficiency is the leading cause of _______ worldwide.
blindness
The skeletal abnormalities of rickets include
bowed legs, thick wrists and ankles, curvature of the spine, a pigeon chest (chest protrudes above the sternum), skull malformations, and pelvic deformities
Plants contain pigments called
carotenoids
Carotenoids may play a role in preventing cardiovascular disease in persons at high risk. This role may be linked to _____
carotenoids' ability to inhibit the oxidation of low-density lipoproteins (LDLs)
In general, humans require a total of about ____ of vitamins for every ______ of food consumed
1 ounce (28 grams) 150 pounds (70 kilos)
When vitamin D levels are adequate, about ______- of dietary calcium is absorbed by the small intestine. If blood levels of vitamin D are low, the small intestine is able to absorb only about _______ of calcium from the diet, which is not enough to maintain the calcium requirements for bone health and other functions.
30-40% 10-15%
When fat absorption is efficient, about ______ of the fat-soluble vitamins are absorbed.
40-90%
what is a coenzyme?
A compound (e.g., water-soluble vitamin) that combines with an inactive enzyme to form a catalytically active form. In this manner, coenzymes aid in enzyme function.
what is a international unit (IU)
A crude measure of vitamin activity, often based on the growth rate of animals in response to the vitamin. Today IUs have largely been replaced by more precise milligram or microgram measures.
What is rickets?
A disease characterized by poor mineralization of newly synthesized bones because of low calcium content. Arising in infants and children, this deficiency is caused by insufficient amounts of the vitamin D hormone in the body.
what is a retina?
A light-sensitive lining in the back of the eye. It contains retinal.
What is macular degeneration?
A painless condition leading to disruption of the central part of the retina (in the eye) and, in turn, blurred vision.
what is a prostate gland?
A solid, chestnut-shaped organ surrounding the first part of the urinary tract in the male. The prostate gland secretes substances into the semen.
what is a provitamin A
A substance that can be converted into vitamin A.
what is Community-supported agriculture (CSA)
Farms that are supported by a community of growers and consumers who provide mutual support and share the risks and benefits of food production, usually including a system of weekly delivery or pickup of vegetables and fruit, and sometimes dairy products and meat.
Vitamin D is a fat-soluble vitamin with two unique qualities. what are those?
First, vitamin D is the only nutrient that is also a hormone. Second, vitamin D is the only nutrient that can be produced in the skin upon exposure to ultraviolet light.
Vitamin A is in a group of compounds known as
Retinoids
vitamins in dairy
Riboflavin Choline] Vitamin D Vitamin B12
what is retinyl
Storage form of vitamin A.
What is a fat soluble vitamin?
Vitamins that dissolve in fat and the substances such as ether and benzene but not readily in water. These vitamins are A, D, E, and K.
What is a water soluble vitamin?
Vitamins that dissolve in water. These vitamins are the B vitamins and vitamin C.
The other two carotenoids that can be converted into vitamin A (though not very effectively) are
alpha-carotene and beta-cryptoxanthin.
Vitamin A is found in
animal sources such as fish, liver, eggs, fortified milk, fortified margarine, and yogurt.
Light entering the eye reaches a lining called the ____. The _____ consists of _________.
retina (x2), rods, cones, and nerve cells
Vitamin D is involved in gene expression and cell growth; it binds to and subsequently affects cells of the
immune system, brain and nervous system, parathyroid gland, pancreas, skin, muscles, and reproductive organs.
Due to the role of vitamin D in calcium absorption, excretion, and release of calcium from bone, supplementation with high doses of vitamin D can cause calcium levels in the blood to ____ above the normal range.
increase
what is hyperkeratosis?
is a condition in which skin cells produce too much keratin, blocking the hair follicles and causing "gooseflesh" or "toadskin" appearance. The excessive keratin in these skin cells causes the skin to be hard and dry.
Vitamin A performs important functions in
light-dark vision and, to a lesser extent, color vision.
The ________ (also known as the macula lutea, meaning yellow spot) is in the central area of the retina and is responsible for the most _______. It contains the carotenoids lutein and zeaxanthin in high enough concentrations to impart a yellow color.
macula detailed central vision
The main function of vitamin D (calcitriol) is to __________. Together with the hormones _________, vitamin D closely maintains blood calcium within a narrow range
maintain the normal range of calcium and phosphorus in the blood. parathyroid hormone (PTH) and calcitonin
Calcium deposits in organs can cause _____ and ____. Toxicity symptoms of too much vitamin D also include
metabolic disturbances, cell death weakness, loss of appetite, diarrhea, vomiting, mental confusion, and increased urine output.
Vitamins are considered _______-, because you need vitamins in much smaller quantities than carbohydrates, fats, and proteins.
micronutrients
Vitamin A-deficient children experience stunted growth. For bones to grow and elongate, _______. Vitamin A assists with _____ of healthy bone tissue
old bone must be remodeled (broken down) so that new bone can be formed breakdown and formation
About 65% of the vitamin A in the typical North American diet comes from _________, whereas_________- dominates in the diet among poor people in other parts of the world.
preformed vitamin A sources provitamin A
The dietary carotenoid lycopene (the red pigment found in tomatoes, watermelon, pink grapefruit, and guava) seems to protect against what type of cancer?
prostate
