Retinol (RET-uh-nol) is the scientific name for vitamin A,
a vitamin found only in animals. It occurs as a yellowish to
orange powder with a slight brownish cast and is a relatively
stable compound. Retinol is converted in the body from an
alcohol to the corresponding aldehyde, retinal (C20H28O), one
of the primary chemical compounds involved in the process
by which light is converted to nerve impulses in the retina of
the eye. Vitamin A is also required for a number of other
biochemical reactions in the body, including growth and
development of tissue and maintenance of the immune system
a vitamin found only in animals. It occurs as a yellowish to
orange powder with a slight brownish cast and is a relatively
stable compound. Retinol is converted in the body from an
alcohol to the corresponding aldehyde, retinal (C20H28O), one
of the primary chemical compounds involved in the process
by which light is converted to nerve impulses in the retina of
the eye. Vitamin A is also required for a number of other
biochemical reactions in the body, including growth and
development of tissue and maintenance of the immune system
Vitamin A is synthesized in animal bodies through a
variety of pathways. One important source of vitamin A is a
group of related compounds called the carotenes, substances
responsible for the yellowish or orangish appearance of
fruits and vegetables such as carrots, sweet potatoes, squash,
cantaloupe, apricots, pumpkin, and mangos. Some leafy
green vegetables, such as collard greens, spinach, and kale,
are also good sources of the carotenes. The most important of
the carotenes is b-carotene (beta-carotene), C40H56. The oxidation
of carotenes in animal bodies converts them to retinol.
The chemical structure of retinol was determined in 1931
by Swiss chemist Paul Karrer (1889–1971), and the compound
was first prepared synthetically shortly thereafter by Austrian-
German chemist Richard Kuhn (1900–1967). The first
successful process for producing retinol commercially was
developed in the mid-1940s by German chemist Otto Isler
(1920–1992), then employed at the pharmaceutical company
Roche, located in Sissein, Germany. Isler’s process involved a
complex series of reactions that begins with the combination
of a fourteen carbon hydrocarbon and a six carbon hydrocarbon
to create the fundamental backbone from which the
retinol molecule is constructed. Regular production of vitamin
A began in 1948 with a projected output of 10 kilograms
per month, which before long was raised to 50 kilograms per
month. The Roche plant at Sissein continues to produce
retinol today.
Vitamin A is probably best known for its role in maintaining
normal vision. Deficiencies of the compound are
likely to manifest themselves earliest in a variety of eye
problems, most commonly night blindness. Night blindness
is a condition in which one loses the ability to distinguish
objects in reduced light. If left untreated, vitamin A deficiencies
may lead to decreased ability to see in normal light and,
eventually, to complete blindness.
But vitamin A has been shown to have a number of other
functions in the body. It is essential for the maintenance of
growth, bone formation, reproduction, proper immune system
function, and healing of wounds. A number of additional
claims have been made for the compound, although evidence
is not as strong as it is for the above functions. For example,
it may be effective in preventing or treating a variety of
conditions such as measles, intestinal parasites, osteoporosis,
inflammatory bowel disease, bone marrow disorders, certain
types of cancer, tuberculosis, peritonitis, osteoarthritis, food
poisoning, Alzheimer’s disease, miscarriage, and HIV/AIDS.
In each of these cases, evidence is not yet strong enough to
show a clear-cut connection between retinol and disease, but
research is being conducted to determine how strong the
association may be.
Retinol is available commercially in a variety of formulations,
including tablets, capsules, and creams. Such products
usually contain a modified form of retinol that is more easily
absorbed by the body. For example, a product known as
tretinoin is a synthetic form of retinol known as all-trans
retinoic acid. The term all trans means that all of the double
bonds in retinoic acid are located on the same side of the
molecule. Products containing tretinoin are used to treat
acne, pimples, wrinkles, blackheads, freckles, sun-spots, and
even pre-cancerous lesions. They work by increasing the rate
with which the skin sheds old cells and replaces them with
new cells.
Vitamin A supplements in pill or capsule form are available
in two formulations, those that contain retinol and
those that contain beta carotene. It is not possible to take
too much of the latter type of vitamin A. The body will not
convert excess amounts of carotene into retinol but will,
instead, excrete the excess in the urine or stool. An excess
of retinol-based vitamin A, by contrast, may result in certain
medical problems. Since the vitamin is fat soluble, in
may be stored in body fat and reach relatively high concentrations
if too much is ingested. An excess of retinol in the
body may be associated with liver damage, osteoporosis,
rash, fatigue, bone and joint pain, nausea, insomnia, and
personality changes.
