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The
Fat-Soluble Vitamins
Vitamin A
There are two basic types of vitamin A - retinoids and beta-
carotene. Retinoids come from animal sources such as liver and
eggs. Beta-carotene comes from plant sources, particularly deep
green, orange or yellow vegetables and fruits.
Vitamin A Functions
1. Vitamin A helps many body processes work. It is most known
for its vision-related functions. People who have mild vitamin
A deficiencies may have night blindness. Those with more severe
vitamin A deficiencies may become totally blind.
2. Vitamin A helps to build the immune system so the body
is more resistant to disease.
3. Vitamin A plays a role in cell growth.
4. Vitamin A is important to healthy fetal development.
5. A vitamin A deficiency can cause the taste buds on the
tongue to be less sensitive.
6. Vitamin A is an antioxidant. Antioxidants protect the body
from some of the negative effects of oxygen. Vitamins C and E
are also antioxidants. The antioxidant vitamins may protect against
cancer, aging, heart disease and other diseases.
Vitamin A Deficiency and Toxicity Symptoms
A lack of vitamin A can produce several symptoms in the body.
Some of these include hardening of the skin, night blindness,
clouding of the cornea, liver damage and reduced growth rate
in children. Vitamin A deficiency is not frequently a problem
in the United States for two reasons. The first is that most
people have enough food to eat. Over eating is a bigger problem
than deficiency. The second reason is that vitamin A is not water-soluble,
so excess amounts can build up in the blood, causing toxicity.
The symptoms of too much vitamin A (toxicity) can range from
headaches and joint pain to dry skin, hair loss and even death.
The RDA for vitamin A is 800 micrograms per day for men and
1000 micrograms per day for women.
Sources of Vitamin A
Good sources of retinoid vitamin A include liver, fish oil,
eggs, margarine and milk that have been fortified with vitamin
A. Good sources of beta-carotene include dark green, leafy vegetables
and deep orange or yellow vegetables. Carrots, squash, broccoli,
spinach and sweet potatoes are all good sources of beta-carotene.
Remember: carrots = carotene!
Vitamin D
Vitamin D is slightly different from the 12 other vitamins.
This is the only vitamin that can be made in the body. When the
skin is exposed to sunlight, the skin cells can make enough vitamin
D to meet the body's needs. Usually, about 15 minutes per day
of exposure to the sun is sufficient. Lighter-skinned and young
people may need less sun, while darker-skinned and older people
may need more. When vitamin D is made by the skin, it is called
a hormone.
 Vitamin D can also be obtained
from foods. When a person gets the vitamin D they need from food
rather than sunlight, vitamin D is a true vitamin. In the United
States, milk is fortified with vitamin D, so even people who
are not frequently in the sun can get enough vitamin D. Eggs,
liver and fish oils are another dietary vitamin D source.
Vitamin D Functions
Vitamin D's major function is to keep the bones supplied with
the calcium they need to stay strong. Depending on how much calcium
the bones need, vitamin D can cause the intestines to absorb
more calcium from food or the kidney to excrete less calcium.
Vitamin D Deficiency and Toxicity Symptoms
A lack of vitamin D in the diet can cause rickets, which is
a disease characterized by weakened bones. Symptoms of rickets
are bowed legs, enlarged head and deformed pelvis. Because vitamin
D is a fat-soluble vitamin, it is possible to have too much in
the body, causing toxicity. Children can have toxic levels of
vitamin D if they consume just 5 times the RDA level. Too much
vitamin D causes weakness, diarrhea, vomiting, mental confusion
and calcium deposits in the organs.
Vitamin E
Vitamin E is an antioxidant, along with vitamins A and C.
Vitamin E prevents free radicals (compounds in the body that
look for electrons) from taking too many electrons from the body
cells. Without vitamin E protecting the cell's electrons, the
cell could be damaged or destroyed.
A vitamin E deficiency could cause destruction of the red
blood cells in both children and adults.
Many people believe that vitamin E can halt or reverse the
aging process or improve sexual function. However, these myths
haven't been scientifically proved.
Vitamin E Deficiency and Toxicity
A vitamin E deficiency can be hard to detect because it can
remain hidden for a long time. Those with the greatest risk for
a vitamin E deficiency are people whose bodies can't absorb fat
because of a disease such as cystic fibrosis. Symptoms of a vitamin
E deficiency are usually neurological disorders that affect the
eyes or spine.
Vitamin E is not a very toxic substance. If a person does
consume too much though (over 500 micrograms per day), they might
have symptoms such as nausea and vomiting, headaches, diarrhea
and fatigue.
Sources of Vitamin E
Foods that contain high amounts of vitamin E include plant
oils (corn, sunflower, safflower, soybean, peanut and others),
margarine, leafy greens, oatmeal, peaches, eggs, liver, nuts,
milk and whole grains. The RDA for vitamin E is 10 milligrams
per day for men and 8 milligrams per day for women. A balanced
diet usually provides an adequate amount of vitamin E.
Vitamin K
The major function of vitamin K is to aid in blood clotting.
Vitamin K is needed by the body to make blood-clotting factors
(agents that help the blood to clot) such as prothrombin. Without
vitamin K, a person who receives a cut or scratch may continue
to bleed. This is because the body can't make the clotting factors
needed to form a scab. Frequently, when a person suffers a cerebrovascular
accident (a stroke), their doctor prescribes a drug that keeps
the blood from clotting too much. People taking these types of
medications should consult their doctor or dietitian before consuming
too much vitamin K because it could interfere with the medicine.
Excess bleeding is the biggest symptom of a vitamin K deficiency.
This is especially dangerous for those about to undergo surgery.
Vitamin K toxicity is very rare because it is removed from the
body easily.
Green leafy vegetables are the best sources of vitamin K.
Food sources include spinach and other leafy greens, green beans,
broccoli and peas. Liver also contains vitamin K. The RDA for
vitamin K is 60-80 micrograms per day for adults. Most people
consume several times this amount, so deficiency is usually not
a problem.
  
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