Vitamin A

 Vitamin A

Introduction

It is an essential human nutrient. It is a fat soluble vitamin

Vitamin A is a generic term for a large number of related compounds(2)

It can be divided into two categories

Ø  Retinoids: in foods of animal origin, the major form of vitamin A is an alcohol (retinol), or as an acid (retinoic acid),they are called performed vitamin A, but can also exist as an aldehyde (retinal).

Ø  Carotenoids : Precursors to the vitamin (a provitamin) are present in foods of plant origin( colored fruits and vegetables ), some of the members of the carotenoid family are beta-carotene, alpha-carotene, and beta- cryptoxanthin .

Among these, beta-carotene is most efficiently made into retinol . Alpha-carotene and beta- cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene.

The discovery of vitamin A stemmed from research dating back to 1906 and it was the first lipo-soluble vitamin to be recognized by Moray 1922.

Sources

The richest food are (liver "beef, pork, chicken” , eggs , butter Milk and its products ).

carrots ,  Broccoli  , sweet potatoes , kale spinach .

Leafy vegetables , pumpkin , mango , apricots and papaya .

Fortified foods( low-fat , skim milk ,  margarine and most ready-to-eat and instant prepared cereals  )are often fortified with vitamin A because it is lost during processing ,  so  it is important to check the label on the package for the vitamin A content to obtain the RDA

2. Supplements:

The principal forms of preformed vitamin A (retinol ) are retinyl palmitate and retinyl acetate .

Beta carotene are common source of vitamin A in supplements.

Both may be combined in supplements

Equivalencies of retinoids and carotenoids (IU)

Vitamin A intake is often expressed in international units (IU) or as retinol equivalents (RE), with 1 micrograms retinol = 3.3 IU =6 micrograms beta carotene.

Recommended daily intake

Vitamin A US Dietary Reference Intake:

900 micrograms (3000 IU) for men

700 micrograms (2300 IU) for women.

Upper limit 3,000 micrograms (10,000 IU).

Role in the body :

Promoting vision (retinol – retinal )

Regulation of gene expression (retinoic acid )

Immunity (retinal and retinoic acid )

Supporting reproduction and growth(retinal)

Red blood cells production

Beta-carotene as antioxidant (4)

Disease Treatment

Vitamin A status

Vitamin A status depends on:

Adequacy of vitamin A stores , 90% of which are in the liver.

A person's protein status because retinol binding proteins serve as the vitamin's transport carriers inside the body .(4)

Nutrient interactions

Zinc

Zinc deficiency is thought to interfere with vitamin A metabolism in several ways affecting  vitamin A nutritional status in humans

Iron

Vitamin A deficiency may exacerbate iron deficiency anemia. (Moreover, studies in rats have shown that iron deficiency alters plasma and liver levels of vitamin A)

Deficiency
 Children who are considered to be at increased risk for subclinical vitamin A deficiency include:

Preschool age children.

Children living at or below the poverty level.

Children with inadequate health care or immunizations.

Children living in areas with known nutritional deficiencies.

Children with diseases of the pancreas, liver, or intestines, or with inadequate fat digestion or absorption.

Manifestations of hypovitaminosis

Night blindness, corneal drying (xerosis), triangular gray spots on eye (Bitot's spots), corneal degeneration and blindness (xerophthalmia) , impaired immunity (Vitamin A deficiency can be considered a nutritionally acquired immunodeficiency disease) , hypokeratosis (white lumps at hair follicles), softening of the cornea (keratomalacia).

Children who are only mildly deficient in vitamin A have    a higher incidence of respiratory disease and diarrhea as well as a higher rate of mortality from infectious  diseases

Vitamin A deficiency in the opt :

22% of children were found to have low vitamin -A plasma levels (<200 μg/L) , Furthermore, more than half of the children participating in the study (53.9%) had levels of vitamin A in the range of 200-299 μg/L , meaning that 75.9% of children had vitamin A levels below 300 μg/L.

The results showed a significant difference between the prevalence of vitamin A deficiency in the West Bank (18.9 per cent) compared to the Gaza Strip (26.5 per cent), but no difference with respect to gender, age groups or refugee status.

Overdose and toxicity
( Hypervitaminosis )

As vitamin A is fat-soluble, disposing of any excesses leads to toxicity.

Children are more vulnerable to toxicity because they need less and are more sensitive to overdoses

vitamin A toxicity occurs when all binding proteins are swamped and free vitamin A damages the cells .

Acute toxicity generally occurs at doses of 25,000 IU/kg.This can lead to nausea, jaundice, irritability, anorexia vomiting, blurry vision, headaches, muscle and abdominal pain and weakness, drowsiness and altered mental status.

Chronic toxicity occurring at 4,000 IU/kg daily for 6-15 months.In chronic cases, hair loss, drying of the mucous membranes, fever, insomnia, fatigue, weight loss, bone fractures, anaemia, and diarrhoea (5)

Overdose and toxicity
( Hypervitaminosis )

Liver toxicities can occur at levels as low as 15,000 IU per day to 1.4 million IU per day, with an average daily toxic dose of 120,000 IU per day.

In people with renal failure 4000 IU can cause substantial damage.

Beta carotene from food is likely to cause this toxicity as it is not converted efficiently enough in the body to vitamin A , it is stored in the fat just under the skin and turn skin yellow . In contrast from supplement is harmful.

Excessive vitamin A over years weakens the bone and contribute to osteoporosis

Birth defects and Safety in pregnancy

Excessive vitamin A  has a teratogenic risk (10000 IU before 7th week of pregnancy).

Some current issues and controversies about vitamin A

Since 1987, WHO has advocated the routine administration of vitamin A with polio, multi-antigen and measles vaccine in countries where vitamin A deficiency is a problem, also supplementation to  postpartum mothers can improve the vitamin A content of their breast milk.(6)

Vitamin A, beta carotene, and cancer

Dietary intake studies suggest an association between diets rich in beta-carotene and vitamin A and a lower risk of many types of cancer

Fontham ETH. Protective dietary factors and lung cancer. Int J Epidemiol 1990;19:S32-S42. [PubMed abstract]

Vitamin A and osteoporosis limited experience data

Results of some studies indicate that long term intake of performed vitamin A of 1500 mcg /day ( not beta carotenes) increases risk of osteoporotic fracture by affecting mineral bone density .

Recommendation to obtain adequate vitamin A :

Vitamin A can be lost from foods during preparation, drying , or storage. To prevent loss of vitamin A:

Use raw fruits and vegetables whenever possible.

Keep vegetables (except sweet potatoes) and fruits covered and refrigerated during storage.

Steam vegetables and braise, broil meats instead of frying. Some of the vitamin A is lost in the fat during frying.

Food labeling to obtain RDA and avoid overdose .

Fortified foods and supplementations

Extra vitamin A to prevent deficiency

World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) recommend vitamin A administration for all children diagnosed with measles,” Measles may increase the body's utilization of vitamin A, possibly because of the rapid destruction of epithelial surfaces”,  in communities where vitamin A deficiency is a serious problem and where death from measles is greater than 1%.

Fat malabsorption can result in diarrhea and prevent normal absorption of vitamin A ( Celiac disease, Crohn's disease, and Pancreatic disorders)

Vegetarians: should choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A

 Give supplements to postpartum women and promoting breastfeeding is the best way to protect babies from VAD.

For deficient children: periodic supply of high-dose vitamin A is indicated .

Vitamin A supplementation reduces severe morbidity and mortality from infectious diseases among children .