Vitamin A

Chemistry: fat-soluble vitamin. Its basic molecule is retinol (vitamin A alcohol). After absorption, retinol is transported via chylomicrons to the liver, where it is either stored as retinol ester or re-exported to the body. It is found in two forms in nature: Retinol ester (vitamin A) or Provitamin A carotenoids (previtamin A).


Sources:
-preformed vitamin A (retinol): animal foods (liver, milk, kidney, and fish oil), fortified foods, and drug supplements.
-provitamin A carotenoids and beta carotenes: plant sources, principally carrots, pumpkin and sweet potato, then green leafy vegetables.


Daily allowance:
The RDAs of vitamin A for various age groups are as follows:

• Infants aged 1 year or younger - 375 mcg
• Children aged 1-3 years - 400 mcg
• Children aged 4-6 years - 500 mcg
• Children aged 7-10 years - 700 mcg
• All males older than 10 years - 1000 mcg
• All females older than 10 years - 800 mcg including pregnant women.
• Lactating women 1300 mcg in the first 6 months and 1200 mcg in the second 6 months.
• Pregnant women do not require increased vitamin A supplementation. In fact, the Teratology Society advocates that women be informed of the possible risk of cranial neural crest defects and other malformations resulting from excessive use of vitamin A shortly before or during pregnancy.

Causes of vitamin D deficiency (VAD):
1-Dietary deficiency
2-Zinc deficiency
3-Iron deficiency
4-Protein deficiency
5-Abetalipoproteinemia
6-Malabsorbtion: like in Sprue, pancreatic insufficiency, post small bowel rescection or bypass, cystic fibrosis, cholestatsis ans inflammatory bowe disease (IBD).


Clinical presentations, signs and symptoms of vitamin D deficiency:
1-night blindness which may progress to complete blindness.
2-increased infections (respiratory, diarrhea..) due to impaired immunity
3-infertility due to impaired spermatogenesis and imaired empryogenesis leading to abortions
4-Bitot spots - Areas of abnormal squamous cell proliferation and keratinization of the conjunctiva in young children.
5-Dry skin, dry hair, broken fingernails and dry eyes (xerophthalmia)

6-Pruritus

7-Keratomalacia and Corneal perforation

8-Follicular hyperkeratosis (phrynoderma) secondary to blockage of hair follicles with plugs of keratin.

9-Decreases growth rate and slowed bone development.

 

 

Laboratory findings and workup:

Serum retinol is expensive but can be performed. Also checking serum albumi, zinc and iron profile may be helpful in 2ry cases.

X-ray of long bones may show bone growth delay and excessive depostion of periosteal bone in children.

Dark-adaptation threshold should be tested.

 

 

Prevention:

The Dietary Guidelines for Americans, from the US departments of Agriculture and Health and Human Services, recommend consumption of a variety of foods for a comprehensive nutrient intake.Vitamin A – rich foods include the following:

• Liver
• Beef
• Chicken
• Eggs
• Whole milk
• Fortified milk
• Carrots
• Mangoes
• Orange fruits
• Sweet potatoes
• Spinach, kale, and other green vegetables

Eating at least 5 servings of fruits and vegetables per day is recommended in order to provide a comprehensive distribution of carotenoids.
A variety of foods, such as breakfast cereals, pastries, breads, crackers, and cereal grain bars, are often fortified with 10-15% of the RDA of vitamin A.

Treatment of vitamin A deficiency:
For subclinical cases, dietary supplementation with fortified souces may be enough.

For VAD syndromes, treatment includes daily oral supplements, as follows:

• Children aged 3 years or younger - 600 mcg (2000 IU)
• Children aged 4-8 years - 900 mcg (3000 IU)
• Children aged 9-13 years - 1700 mcg (5665 IU)
• Children aged 14-18 years - 2800 mcg (9335 IU)
• All adults - 3000 mcg (10,000 IU)

Therapeutic doses for severe disease include 60,000 mcg (200,000 IU), which has been shown to reduce child mortality rates by 35-70%.

Always refer to your physician before taking or giving your kids any vitamin or medication.