Chapter 11 Fat soluble vitamins
What are the three ways vitamin D raises blood concentrations of bone minerals?
- When the diet is sufficient, vitamin D enhances mineral absorption from the GI tract - When the diet is insufficient, vitamin D provides the needed minerals from other sources: reabsorption by the kidneys and mobilization from the bones into the blood - Vitamin D may work alone, as it does in the GI tract, or in combination with parathyroid hormone, as it does in the bones and kidneys.
What are the major roles of vitamin A?
-Promoting vision -Participating in protein synthesis and cell differentiation, thereby maintaining the health of epithelial tissues and skin -Supporting reproduction and regulating growth
What does one microgram of retinol count as in RAE?
1 RAE, just as 12 micrograms of dietary beta-carotene
How long would it take for vitamin A deficiency symptoms to appear if a person stopped eating it?
1-2 years for a healthy adult, but much sooner for a growing child
What do the WHO and Nations International Children's Emergency Fund (UNICEF) recommend for children with measles?
2 doses of vitamin A supplements, given 24 hours apart
What is the UL for vitamin A?
3000 micrograms for adults, which applies only to the preformed vitamin
What is the RDA for vitamin A?
700 micrograms for women 900 micrograms for men
Vitamin A status depends mostly on the adequacy of vitamin A stores, ______ percent of which are in the liver.
90
What is the active form of vitamin D?
A hormone
When light passes through the cornea of the eye and strikes the retina, rhodopsin responds Then...
As it does, opsin is released and retinal shifts from a cis to a trans configuration, just as fatty acids do during hydrogenation
What major roles does beta-carotene play in the body?
First, it serves as a vitamin A precursor, Second some beta-carotene acts as an antioxidant capable of protecting the body against disease
Where is more vitamin A found than in the retina?
In the cells lining the body's surfaces
Although overconsumption of beta-carotene from foods may turn the skin yellow, is it harmful?
No
Do massive doses of vitamin A help acne?
No
Do plants contain retinoids?
No
Can beta carotene, which is found in a variety of fruits and veggies contribute to vitamin A toxicity?
No, because it is not converted efficiently enough. It is just stored in the fat under the skin
Is vitamin A deficiency common in the US?
No, but it is in developing countries
Do beets and corn have vitamin A?
No, they are made from xanthophylls, which are pigments found in plants responsible for the color changes seen in autumn leaves.
What foods have significant sources of vitamin A?
Retinol: fortified milk, cheese, cream, butter, fortified margarine, eggs, liver Beta-carotene: spinach and other dark green, leafy vegetables, broccoli, deep orange fruits (apricots, cantaloupe) and vegetables (squash, carrots, sweet potatoes, pumpkin)
The epithelial tissue on the outside of the body is made of what?
Skin, vitamin A, and beta-carotene, which help protect against skin damage from sunlight
Severity of the measles virus in developing countries often correlates with what?
The degree of vitamin A deficiency; deaths are usually due to related infections such as pneumonia and severe diarrhea
Without vitamin A what happens to the goblet cells in the GI tract?
They diminish in number and activity, limiting their secretions
What does vitamin A deficiency affect on the epithelial cells of the skin?
To change shape and begin to secrete the protein keratin, causing the skin to become dry, rough, and scaly
What helps support immune functions?
Vitamin A
What is blindness due to a lack of vitamin A known as?
Xerophthalmia
Is overconsumption of beta-carotene from supplements from supplements harmful?
Yes
rhodopsin
a light-sensitive pigment of the retina that contains the retinal form of vitamin A and the protein opsin.
What is retinol activity equivalents (RAE)?
a measure of vitamin A activity; the amount of retinol that the body will derive from a food containing preformed retinol or its precursor, beta-carotene.
pigment
a molecule capable of absorbing certain wavelengths of light so that it reflects only those that we perceive as a certain color.
In excess, what may beta-carotene act as?
a prooxident
What is each rhodopsin molecule composed of?
a protein called opsin bounded to a molecule of retinal, which plays a central role in vision
What is a teratogen?
a substance that causes abnormal fetal development and birth defects.
What may excessive vitamin A during pregnancy lead to?
abnormal cell death in the spinal cord, which increases the risk of birth defects including spina bifida and cleft palat
How much vitamin A do multivitamins normally supply?
about 1200 - 1500 micrograms; much more than most people need
The beta-carotene in dark green, leafy vegetables is ________, but masked by large amounts of the green pigment ____________.
abundant chlorophyll
What is essential to achieving peak bone mass before age 30?
adequate nutrition and regular exercise
Why is vitamin A lost when milk is skimmed?
because it is fat soluble. So they are fortified to provide the same amount as in whole milk
Why does vitamin A status depend on a person's protein status?
because retinol-binding protein serves as the vitamin's transport carrier inside the body.
When are high intakes (daily supplemental intakes of vitamin A equivalent to roughly four times the RDA for women) to be the most damaging during pregnancy?
before the 7th week
What is the carotenoid with the gretest vitamin A activity?
beta-carotene
What carries vitamin D to target organs, most notable the intestines, kidneys, and bones?
binding protein
What does vitamin D contribute to along with other nutrients such as vitamin A and K, the hormones parathyroid and calcitonin, the protein collagen, and the minerals calcium, phosphorus, magnesium, and fluoride?
bone making and maintenance
What other tissues respond to vitamin D?
brain and nerve cells muscle cells immune system regulate cells of adipose tissue
How do organs respond to vitamin D?
by making the minerals needed for bone growth and maintenance available.
What does mucus do?
coats and protects the epithelial cells from invasive microorganisms and other potentially damaging substances, such as gastric juices.
Role of vitamin D in the immune system
defends against infectious diseases
What is preformed vitamin A?
dietary vitamin A in its active form.
Adverse effects of beta-carotene supplements are most evident in people who:
drink alcohol and smoke cigarettes.
Role of vitamin D in the muscle cells
encourages growth in children and preserves strength in adults
What cells does vitamin A help to promote?
epithelial and goblet
What are the richest sources of retinoids?
foods derived from animals;liver, fish liver oils, milk and milk products, butter, and eggs
Providing vitamin A to children diagnosed with measles reduces the risk of dying by ________.
half
What does Retinoic acid act like?
hormone, regulating cell differentiation, growth, and embryonic development
Where is retinal active?
in vision and is also an intermediate in the conversion of retinol to Retinoic acid
Role of vitamin D in the adipose tissue
influence the development of obesity
Much of the retinal is converted back to what?
its active cis form and combined with the opsin protein to regenerate rhodopsin.
What is the second stage of xerophthalmia?
keratomalacia (KARE-ah-toe-ma-LAY-shuh), the softening of the cornea that leads to irreversible blindness.
What causes night blindness?
lack of vitamin A at the back of the eye, the retina
What causes total Blindness?
lack of vitamin A at the front of the eye, the cornea
Beta-carotene's absorption and conversion are significantly _______ efficient than those of the retinoids.
less
What are the tissues that line the inside of the body that vitamin A helps to maintain?
mucous membranes found: the linings of the mouth, stomach, and intestines; the linings of the lungs and the passages leading to them; the linings of the urinary bladder and urethra; the linings of the uterus and vagina; and the linings of the eyelids and sinus passageways.
What is one of the first detectable signs of vitamin A deficiency and promotes early diagnosis?
night blindness
What happens when a vitamin A deficiency causes less mucus?
normal digestion and absorption of nutrients falter, and this, in turn, worsens malnutrition by limiting the absorption of whatever nutrients the diet may deliver
What does retinol (vitamin A) help support with reproduction in women?
normal fetal development during pregnancy
What may some retinal become?
oxidized to retinoic acid, a biochemical dead end for the visual process
xerophthalmia
progressive blindness caused by inadequate mucus production due to severe vitamin A deficiency.
Role of vitamin D in the brain and nerves
protects against cognitive decline and slows the progression of Parkinson disease.
What does vitamin A in the cells lining the body's surfaces participate in?
protein synthesis and cell differentiation
Visual activity leads to what?
repeated small losses of retinal, necessitating its constant replenishment either directly from foods or indirectly from retinol stores.
What does retinol support?
reproduction and is the major transport and storage form of the vitamin
What do vitamin A deficiencies cause in many countries around the world?
responsible for a million or more unnecessary deaths and cases of blindness each year.
What are two forms of acne fighting agents that are made from vitamin A?
retin-a Accutane
How are vitamin A's recommendations expressed?
retinol activity equivalents (RAE)
What has been genetically modified for countries who do not eat enough vitamin A or beta carotene?
rice; Commonly called golden rice because of its yellowish tinge, this rice offers a promising solution to world malnutrition
What does beta-carotene look like?
rich, deep yellow, almost orange, compound
night blindness
slow recovery of vision after flashes of bright light at night or an inability to see in dim light; an early symptom of vitamin A deficiency.
vitamin A participates in the dismantling of what?
small bones to make larger ones
What does retinol (vitamin A) help support with reproduction in men?
sperm development,
What roles does vitamin A play in the eye?
t helps maintain a crystal-clear outer window, the cornea (KOR-nee-uh), and it participates in the conversion of light energy into nerve impulses at the retina
What is the first stage of xerophthalmia?
the cornea becomes dry and hard because of inadequate mucus production—a condition known as xerosis
What is remodeling?
the dismantling and re-formation of a structure.
retina
the innermost membrane of the eye, composed of several layers, including one that contains the rods and cones.
What is cell differentiation?
the process by which immature cells develop specific functions different from those of the original that are characteristic of their mature cell type.
opsin
the protein portion of visual pigment molecules.
cornea
the transparent membrane covering the outside of the eye.
With the help of vitamin A and the bone dismantling cells, what happens to selected sites in the bone?
they are destroyed because they are not needed
What happens when a child lacks vitamin A?
they fail to grow; given vitamin A supplements, these children gain weight and grow taller.
What is vitamin D's specific role in bone health?
to assist in the absorption of calcium and phosphorus, thus helping to maintain blood concentrations of these minerals. The bones grow denser and stronger as they absorb and deposit these minerals.
What inhibits replication of the measles virus?
vitamin A
What do many vegetables and some fruits contain?
vitamin A precursors (carotenoids)
What may excessive intake of vitamin A do to the bones?
weaken them and contribute to fractures and osteoporosis
When do Vitamin A toxicity symptoms start to develop?
when all the binding proteins are loaded, and vitamin A is free to damage cells
When may vitamin A toxicity occur since it is very unlikely?
when concentrated amounts of preformed vitamin A in foods derived from animals, fortified foods, or supplements are consumed
How do many countries nourish their people with vitamin A?
with biofortified corn, rice, and cassava to protect against vitamin A deficiencies