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|
| Proper name |
Retinol
|
| Category |
Vitamin
|
| Functions |
Essential
for the formation of visual purple (rhodopsin), the pigment in the eye that
allows vision.
Essential for maintaining the integrity of epithelial tissue, i.e., the
skin and mucus membranes, and linings of many organs and tissues.
Supports immune function, primarily by maintaining the health of the skin
and mucus membranes, thus creating a barrier to infection. Vitamin A is
also an anti-oxidant.
Helps reduce the risk of cancer, particularly of epithelial cell cancers
such as cancers of the mouth, bladder, skin, stomach, cervix and breast.
This effect is best documented for the ingestion of natural sources of beta
carotene.
Necessary for the growth of bone and teeth, especially the enamel of teeth,
and for the growth of soft tissue as well.
Required for sexual maturation during adolescence and for adult reproductive
health as well. Deficiency of vitamin A can cause degeneration of the reproductive
glands and sterility. |
| RDA |
Men
5,000 IU, Women
4,000 IU, Pregnant 5,000 IU, Lactating 1,200 IU, Children 2, 000 to 4,000
IU |
| Therapeutic
dose |
10,000
to 25,000 IU. Doses in excess of 100,000 IU have been used under medical
supervision. - Persons with hepatitis, cirrhosis, gall stones or other impediments
to normal amounts of bile in the intestines may need to take the micellized
form of vitamin A. - Persons with pancreatitis or cystic fibrosis may need
to take the aqueous or micellized forms of vitamin A. |
| Toxicity |
Toxic
effects have been reported in adults taking over 50,000 IU oil soluble vitamin
A daily for several years and one case of taking 18,500 to 60,000 IU of
water soluble A for several months. On the other hand, doses as high as
1,000,000 IU have been taken for 5 years without toxicity. Vitamin A excess
is the most common cause of vitamin toxicity. - Symptoms of hypervitaminosis
A include: dry itchy skin, brittle nails, hair loss, bone pain, gingivitis,
headaches, muscle and joint pain, thickening of long bones, loss of hair,
superficial retinal hemorrhages, exopthalmos (bulging eyes), anorexia, jaundice,
fatigue, diarrhea, susceptability to infections, night sweats, peripheral
edema, headaches (from increased intracranial pressure), hepatic enlargement
and dysfunction, and tingling in the extremities. - Fetal malformations
were noted in the fetus of a mother who ingested 150,000 IU of vitamin A
daily for 2 months around the time of conception. |
| Best
forms
|
Micellized
or Aqueous Deficiency symptoms - Night blindness or poor night vision. Drying
and hardening of the epithelial tissue of the eye and in extreme cases,
blindness. - Dry, scaly rough skin with small, hard bumps (hyperkeratinosis).
- Bone deformities and dental carries. - Lack of sexual maturation or functioning.
|
| Food
sources |
Halibut
or cod liver oil, liver, egg yolk, butter, cream and kidney are food sources
of vitamin A. There are many plant sources of pro-vitamin A, i.e., beta
carotene. |
| Lab
tests |
Serum
vitamin A. |
| Drug
interactions |
Vitamin
A is depleted with ingestion of mineral oil, Colestipol, Cholestyramine
and Neomycin. Nutrient interactions - Works well with other nutrients. Facilitates
zinc absorption. Requires vitamin E for absorption. |
| Metabolism |
Vitamin A is fat soluble and needs to be consumed with fat in order to
be absorbed. Pancreatic lipase is needed to split fats into smaller units
and mix them with water (hydrolysis) in the upper intestine. Bile is needed
so that vitamin A may be transported with fat and bile in minute globules
called micelles to the intestinal wall. - Vitamin A may be produced in
the body by splitting beta carotene in the intestines. Beta carotene is
found in plants and is composed of two vitamin A molecules joined head
to head. An enzyme in the intestines separates the molecules. - 90% of
the body's vitamin A is stored in the liver. These stores can last 6-12
months on average without additional intake of vitamin A.
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