Vitamin A

Vitamin A
A pale-yellow alcohol, soluble in fat but not in water.
In pure form, it is readily destroyed by oxidation and
light, which may cause losses during storage.
Source. Vitamin A is found in all animal tissues,
although it is particularly concentrated in the liver.
There are two different dietary sources for the vitamin:
animal sources which contain vitamin A itself,
mostly in the formof retinyl esters, and plant sources
which contain carotenoids that are converted to
vitamin A in animal tissues such as the absorptive
cells in the intestine. The most vitamin A–enriched
animal food source is fish liver oil. Plant carotenoids
are found in green and yellow fruits and vegetables
such as carrots, apricots, asparagus, broccoli, and
green leafy vegetables. Some fresh-water fish contain
vitamin A2, which differs slightly from vitamin A in
structure.

Bioassay. The vitamin A activity of carotenoids
varies with their chemical structure, with β-carotene
being the most potent. One international unit (IU)
of vitamin A has been set at 0. 3 microgram of vitamin
A or 0. 6 μg of β-carotene. This is somewhat
confusing since the efficiency of conversion of
β-carotene to vitamin A becomes greater in a deficiency
state. Although biological assays are sometimes
used, vitamin A and carotene are usually determined
by spectrophotometric techniques.

Physiological activities. In vitamin A deficiency,
the epithelial tissues of many organs are affected.
Growth failure occurs, and young animals can
suffer from neurological symptoms resulting from
pressures on the central nervous system. Changes
occur in the skin, mouth, respiratory tract, urogenital
tract, and some glands. Vitamin A deficiency is also
strongly associated with depressed immune function
and higher morbidity and mortality due to infectious
diseases such as diarrhea, measles, and respiratory
infections. A severe manifestation of vitamin A deficiency
is night blindness and inflammation of the
eyes (xerophthalmia), followed by irreversible blindness.
The symptoms seen in vitamin A deficiency
reflect the multiple roles of this compound in animals.
These roles are fulfilled by two compounds
that are synthesized from vitamin A in the body: vitamin
A aldehyde (retinaldehyde), which is critical
for vision, and vitamin A acid (retinoic acid), which
controls many physiological functions in both the
embryo and the adult. The similar chemical structures
of vitamin A, retinaldehyde, and retinoic acid
are shown at right.

Retinaldehyde. Retinaldehyde has a critical role in
sight. This compound binds to a protein termed
opsin to generate the visual pigment rhodopsin in
the retina. Rhodopsin is the “visual antenna” that
responds to light by sending signals to the brain.
Following absorption of light, rhodopsin releases
the bound vitamin A compound. Resynthesis of
rhodopsin by providing fresh molecules of retinaldehyde
is therefore essential for normal vision.

Retinoic acid. Retinoic acid is the active vitamin A
metabolite that is critical for many processes, such as
cell growth and differentiation, in the embryo and in
the adult. Retinoic acid exerts its effects by modulating
the expression of many genes. This activity is due
to the ability of the compound to control the activities
of proteins known as retinoid nuclear receptors.
When activated by retinoic acid, these proteins bind
to deoxyribonucleic acid (DNA) and regulate gene
transcription. Retinoic acid is currently used in treatment
of various pathologies such as skin disorders
Vitamin A: all-trans -retinol
11-cis -Retinaldehyde
All-trans -retinoic acid
9-cis -Retinoic acid
OH
O
O
OH
O OH
and certain types of cancer. See DEOXYRIBONUCLEIC
ACID (DNA).

Anti-Aging Skin Treatments

A big part of that is using what the American Academy of Dermatology (AAD) describes as by far the most beneficial, age-busting product available: sunscreen. Without a daily skin regimen that includes copious amounts of sunscreen (SPF 30 or higher) on all sun-exposed skin, no other anti-aging products matter, Neronha said.

While sunscreen prevents damage, other products can fight the wrinkles, sagging and brown spots that aging skin may already have. Some research-proven ingredients to look for include:

Retinol - Skin care professionals consider this form of Vitamin A the gold standard of effective topical treatments. Also available as prescription strength Retin-A, retinol is an ingredient in myriad over-the-counter products. It ramps up cell turnover in the top layers of the skin, decreasing wrinkles and improving skin tone, according to Neronha.

Retinol is the whole vitamin A molecule. In order to be active on skin cells, retinol must be broken down into retinoic acid in order to exert its action. Retinoic acid is also called tretinoin. Tretinoin is the active ingredient in prescription products such as Renova and Retin A.
Collectively, retinol and retinoic acid are referred to as retinoids. Retinoids are used in skin care to help slow down skin aging by increasing the production of collagen and hyaluronic acid. They may be used to treat photoaging, acne, pigmentation disorders such as melasma and solar lentigos, as well as rosacea. The result for users is a younger looking, smoother and more luminous skin.
Retinol does need to be available in decent concentrations in order to be effective. If a product doesn’t reveal how much retinol it contains, chances are that it’s negligible and may not deliver any significant benefit to your skin.
Retinol is very light and air sensitive, breaking down down quickly if exposed. When looking for a retinol cream, it’s extremely important to select products with packaging that will maintain the potency of the active ingredient. Jars, tubes and transparent containers are no-nos. Instead, opt for retinol products packaged in opaque, airless pumps. Because the product is protected from air and light, you can be assured that your product is active from the moment it’s opened until it’s finished.

How does Retinol Work?
Retinol breaks down into retinoic acid upon application to skin. Once absorbed, it encourages skin cells to communicate and function normally, a process that is often disrupted during the natural aging process. When skin cells communicate and function correctly, there are several benefits to skin:
· Increase in cell turnover in the top layer of skin (epidermis). The production of new skin cells causes skin to look brighter and smoother
· Stimulation of collagen production which leads to the appearance of smoother and plumper skin
· Reduces pigmentation associated with sun damage
In addition, retinol has been shown to help shrink oil glands which can reduce pore size and diminish scars. It may be helpful in the treatment of acne. Retinol also possesses antioxidant ability to help in the fight against free radicals, which can age skin.

Retinol Benefits
Retinol is an important part of any anti-aging skin care regimen. It offers the following benefits to skin:
· Tighten skin, diminish wrinkles and make your skin feel and look younger.
· Help skin look smoother with a luminescent glow.
· Help pores appear smaller, even out skin tones, and lighten discolorations.
· Cleanse pores and eliminate blemishes.