Vitamin A

Also known as Retinol.

Vitamin A

Vitamin A (retinol), a fat-soluble lipid , is either derived directly from animal foods such as liver, egg yolks, cream, or butter or is derived from beta- carotene , a pigment that occurs in leafy green vegetables and in yellow fruits and vegetables. Vitamin A is essential to skeletal growth, normal reproductive function, and the health of the skin and mucous membranes. One form, retinal, is a component of visual purple, a photoreceptor pigment in the retina of the eye (see vision ). In addition, beta-carotene, like other carotenoids, is now recognized as an important antioxidant.

A deficiency of vitamin A can cause retarded skeletal growth, night blindness, various abnormalities of the skin and linings of the genitourinary system and gastrointestinal tract, and, in children, susceptibility to serious infection. The eye disorders that result from a deficiency of vitamin A can lead to permanent blindness. Severe deficiency can cause death. As with the other fat-soluble vitamins, conditions that lead to an inability to absorb fats, such as obstruction of bile flow or excessive use of mineral oil, can produce a deficiency state. Overconsumption of vitamin A can cause irritability, painful joints, growth retardation, liver and spleen enlargement, hair loss, and birth defects. The National Research Council recommended daily dietary allowance for adults is 1,000 micrograms (retinol equivalents) for men and 800 micrograms for women.

What is Vitamin A?

Vitamin A is a fat-soluble nutrient that we obtain by ingesting animal fats, and which is stored in the liver. Our intestines are also able to manufacture this nutrient from beta-carotene, which is a carotenoid found in vegetables, especially carrots.

How can Vitamin A benefit you?

Vitamin A is a powerful antioxidant. Antioxidants can neutralize free radicals, which are highly reactive chemical substances in the body that can damage cellular material, causing premature disease and aging.

It is also a nutrient that plays essential roles in maintaining healthy vision - warding off night blindness; keeping skin cells healthy - alleviating skin disorders such as psoriasis, and often used in derivative form (prescription Retin-A) to treat acne and wrinkles; boosting the immune system; and healing wounds.

Other studies show vitamin A may help the important hormone insulin regulate blood sugar levels, and, therefore, may benefit people with diabetes.

Precautions about Vitamin A

Vitamin A, though crucial for good health, is one of the most potentially toxic if too much is ingested. Liver, especially, is extremely high in this vitamin because reserves are stored there. The RDA is currently set at,000 IU (International Units) for women and,000 IU for men. Some symptoms of toxicity can manifest as dry skin that easily cracks, soft and brittle nails, hair loss, fatigue, and nausea.

Opinion

Vitamin A is an important nutrient. Elderly people are often deficient in this nutrient due to poor dietary intake; in addition, the Western diet in general is high in processed foods, refined grains, and sugary snacks that all present poor sources.

Alarming studies have even now shown that, due to modern farming methods, the nutrient value in even healthy foods have declined drastically, making the use of supplements more important than ever.

As such, we believe that supplementing with Vitamin A should be considered. On the other hand, for most people, we don't believe the RDA should be exceeded due to potential toxicity. Only those who have consulted a physician and are looking for therapeutic benefit to treat a particular condition should consider taking more than the RDA.

Tips on Choosing a Vitamin A Supplement

• Vitamin A works synergistically with Vitamin E. As such, we recommend you take them together.
• Beta Carotene, as mentioned before, is changed to vitamin A only when the body has a need for it. Therefore, beta carotene cannot induce toxicity. There are some difference between beta carotene and vitamin A, however, so you may want to include both in your diet. We recommend choosing a supplement that contains both vitamin A and beta carotene.

Functions:

• Important catalyst for innumerable biochemical processes
• Antioxidant
• Reproductive function
• Growth and development - bone and cartilage development - cell membrane stability
• Epithelial tissue maintenance - mucous secretions
• Skin and mucosal membrane integrity
• Healthy hair
• Adrenal function
• Immune system response, Resistance to infection
• Required for good vision
• Constituant of visual pigments for color vision
• Helps to manufacture visual purple for night vision

Deficiency symptoms:

• Faulty tooth formation
• Skin problems
• Dry skin
• Itching
• Hyperkeratosis
• Nyctalopia
• Xerophthalmia
• Night blindness
• Loss of sense of taste

What is Vitamin A?

This vitamin is a clear yellow oil, that is fat soluble. The other three vitamins that are fat-soluble are D, E and K. Fat-soluble means it is absorbed and transported round the body in a similar way to fats. The chemical name for Vitamin A is Retinol. The body can also convert a substance called beta-carotene into Vitamin A too.

Where is it found?

As Vitamin A is a fat-soluble vitamin, it occurs in foods that contain fat such as fish oils, dairy produce, some seafoods, butter, whole milk, egg yolks and especially liver.

Beta-carotene is found in orange and green leafy vegetables. The darker the colour the more beta-carotene it contains. For example, spinach contains less beta-carotene than dark outer leaves of a savoy cabbage. Vegetables and fruit rich in beta-carotene are sweet potato, butternut squash, mangoes, apricots, broccoli, turnip greens, and cos lettuce. Fish oil, especially cod liver oil is sometimes used to make Vitamin A supplements.

Why is it needed?

It is needed for the healthy maintenance of skin especially skin that secretes mucous. If there is a deficiency then alterations in the skin can occur. The skin can go on to resemble skin of a pre-cancerous condition and given the right circumstances it could lead to cancer.

Vitamin A is needed for good night vision.

What happens if you are deficient?

Eye and bone development growth is inhibited and night blindness can occur too. A stunting of growth can occur with infertility problems too.

What conditions has it been used to treat?

Primary:

• Coeliac disease, (in cases of deficiency)
• Infection
• Night blindness

Secondary:

• Bronchitis
• Immune function
• Menorrhagia (heavy menstruation)
• Peptic ulcer
• Wound healing
• Acne

How much is normally taken?

Up to 25,000 IU or 7,5000 IU per day is considered safe, however there are contraindications if you are pregnant (refer to side effects and contraindications section below).

Are there any contraindications or side effects?

Excess Vitamin A is stored in the liver for up to two years. An overdose of Vitamin A can lead to bone and joint pain due to toxicity, other symptoms are skin dryness, itching and flaking of skin, hair loss, weakness, headaches, and problems with vision.

Pregnant women or those who think they are pregnant should not take more than 10,000IU (3,000 mcg) per day.

Deficiency Symptoms

• Night blindness:
  The prevalence of individuals with a history of night blindness (or local names for this condition) can serve as a useful indicator of VAD. Specialists can make quantitative measurements of dark adaptation, but these measurements can be difficult to standardize under field conditions. Also, the low prevalence of positive findings limits the use of night blindness in populations with mild to moderate levels of vitamin A deficiency.
• Xerophthalmia:
  Eye signs such as conjunctival xerosis and Bitot's spots can indicate the existence of VAD. However, these signs are somewhat variable and subjective so health workers must be carefully trained for accurate diagnosis. Additionally, the low prevalence of these findings means that very large samples are required to establish the disorder with any certainty, especially if only mild or moderate levels of deficiency are present. For these reasons the quantitative assessment of xerophthalmia is not likely to be a practical measure in populations with mild or moderate deficiency.
• Conjunctival impression cytology:
  In this technique filter paper is applied to the conjunctiva to remove epithelial cells, which are then classified histologically as positive or negative. The method is simple and minimally invasive and may provide an indication of the likelihood of deficiency for surveillance purposes. However, the results indicate only the positive findings and do not provide a continuous scale of deficiency. Moreover, interpreting the samples requires careful training and standardization. For these reasons conjunctival impression cytology falls short of providing a reliable, quantitative index of vitamin A status.
• Serum retinol:
  Measurement of retinol has been widely used to determine vitamin A status at the population level. The proportion of individuals with low retinol levels reflects the risk of deficiency. However, retinol does not reflect liver stores of vitamin A and may be affected by other factors such as infection and protein-energy malnutrition. Also, the method may not be practical under field conditions because of the need for venous blood samples, careful storage and transport of specimens, and sophisticated laboratory analysis. Retinol can be measured in a microsample of serum. The use of a filter paper and the Dried Blood Spot (DBS) method has been developed and used in India, Liberia, Mexico and Nepal, with the advantage that only a finger-prick by sterile lancet is required.
• Breastmilk vitamin A concentration:
  This is a unique indicator of vitamin A status because it provides information about the vitamin A status of both the mother and the breast-fed infant. The mother's secretion of vitamin A into the milk is directly related to her vitamin A status, at least when her vitamin A status is inadequate. All infants are born with low stores of vitamin A, thus the concentration of vitamin A in the breastmilk also serves as an indicator of an infant's likely vitamin A status.
• Relative dose response (RDR):
  Dose-response tests, based on measuring retinol response to an administered dose of vitamin A, measure vitamin A status more accurately. These tests have the significant advantage of reflecting liver stores of vitamin A; however, their acceptability is limited by the requirement that two blood samples be drawn. The modified relative dose-response (MRDR) test requires only a single venous sample, but it is complex for field application and its use as an indicator in continuing ongoing surveillance may be limited.
• Retinol-binding protein:
  The potential for retinol-binding protein to indicate vitamin A status is being explored. This test is highly correlated with serum retinol because it is the carrier protein for retinol in the circulation. When used as an indicator it has many of the limitations of serum retinol, including depression in response to infections and the lack of the ability to reflect liver stores. However, it has the advantage of being potentially measurable in a dried blood spot sample suitable for field application.

What is Vitamin A Deficiency (VAD)?

It is now estimated that correcting VAD can reduce child mortality by about 23%. Even moderate VAD significantly increases a child's risk of dying from an infectious disease. Children with VAD are more likely to have severe measles and severe or prolonged diarrhoea. Severe VAD can also cause blindness, and is indeed the primary cause of childhood blindness worldwide.

One of the first clinical signs of VAD is a difficulty or inability to see in dim light such as at dusk or at night. This condition is called 'night blindness', but often also has a local name.

However, the vast majority of children with VAD have no clinical signs.

What causes Vitamin A Deficiency (VAD)?

VAD occurs when insufficient vitamin A is consumed in the diet, too little is absorbed from foods eaten, or too much is lost due to illness. VAD also occurs when body stores are depleted at times of high requirement, such as during illness (particularly measles and diarrhoea), pregnancy and lactation, and phases of rapid growth.

Non-breastfed infants and children between the ages of-59 months experience more serious effects of VAD than any other groups, but pregnant and lactating women are also at high risk of VAD.

There are two main food sources rich in vitamin A:

• animal (eggs, liver, milk)
• plant (orange/yellow fruits and vegetables, green leafy vegetables)

The bioavailability of vitamin A from plant sources is lower than that of animal sources.

How can VAD be Prevented and Eliminated?

The elimination of VAD can best be achieved through a comprehensive approach that combines strategies. There are four main types of intervention for VAD:

• Supplementation
• Food fortification
• Dietary modification
• Infection control