Vitamin A deficiency

Introduction to vitamin A deficiency Vitamin Adeficiency is a systemic disease caused by the lack of vitamin A in the body. The main pathological change is the keratin degeneration of whole body epithelial tissue. Ocular symptoms appear earlier and significantly, and the ability to adapt to darkness is reduced, followed by conjunctival, corneal dryness, and finally corneal softening, and even perforation, so there are nightblindness, xerophthalmia, and keratomalacia. Etc., the disease is more common in infants and young children with malnutrition and long-term diarrhea. The peak incidence of infants and young children is more than 1 to 4 years old. It is rare to see more than 6 years old. It is more common in Asian and African developing countries. It is not rare in remote areas of China. . basic knowledge The proportion of illness: 0.025% Susceptible people: more than 1 to 4 years old Mode of infection: non-infectious Complications: dystrophy in children, corneal softening

Vitamin A deficiency

(1) Causes of the disease

1. Inappropriate diet When the baby is born, his liver stores little vitamin A and is quickly consumed. However, the content of colostrum is extremely high. Human milk and milk are the main sources of vitamin A needed by the baby. Other foods such as vegetables and fruits Eggs and liver can supply enough vitamin A, so proper diet can provide enough vitamin A, not to cause deficiency, but the food in infants is simple, such as insufficient milk, and no supplementary food, easy to cause subclinical Vitamin A deficiency, after weaning, if you use rice cake, batter, porridge, fat-free milk and other foods for a long time, without supplements rich in protein and fat, it can cause deficiency.

2, digestive diseases, digestive system of chronic diseases such as long-term diarrhea, chronic dysentery, intestinal tuberculosis, pancreatic diseases, etc. can affect the absorption of vitamin A, the liver is the main organ of vitamin A metabolism and storage, bile acid emulsifiable fat in bile Class, promotes the absorption of vitamin A, and can enhance the activity of -carotene-15,15 -oxygenase, and promote its conversion to retinol. Therefore, patients with hepatobiliary diseases such as congenital biliary atresia and chronic hepatitis, Prone to vitamin A deficiency, hepatitis caused by various viruses or toxic hepatitis complicated by infectious diseases, can also cause vitamin A deficiency, should be vigilant.

3, consumptive diseases such as chronic respiratory infections, prolonged pneumonia, measles, etc., on the basis of insufficient intake of vitamin A, due to increased consumption of vitamin A and symptoms, in addition, long-term intake of mineral oil (such as liquid paraffin Etc.), neomycin and methotrexate drugs can also affect the absorption of vitamin A, malignant tumors, urinary system diseases can increase the excretion of vitamin A, protein deficiency affects the synthesis of retinol transporters, causing vitamin A to try to lower in plasma , resulting in a lack of symptoms.

4, hypothyroidism and diabetes can make the conversion of beta carotene into retinol, resulting in a lack of vitamin A, and blood and skin accumulate a large amount of carotene, much like jaundice, but the bulbar conjunctiva is not yellow .

5, zinc deficiency and vitamin A combined with pre-albumin and vitamin A reductase are reduced, so that vitamin A can not be used and excreted, vitamin A deficiency can also occur, in recent years reported changes in nutritional status, also have an impact on the use of vitamin A .

(two) pathogenesis

Vitamin A exists in two forms, namely -ionone (beta-ionone) and its derivatives and provitamin A, also known as carotenoids. The participants are all fat-soluble. The former is an unsaturated one. Alcohols, which act in the form of retinol (vitamin A1) and 3-dehydroretinol (vitamin A2), which are found in the liver, fat, milk and egg yolk of mammals and marine fish. Vitamin A2 is found in the liver of freshwater fish and in the birds that feed these fish. The bioavailability of the latter is only 40% of the former. Carotenoids are an olefinic compound, mainly from plants, the most important of which is . Carotenoid-15,15 -oxygenase cleaves to produce two molecules of retinol, which are transported through the lymphatics of the intestinal mucosa to the liver for storage, and the retinol in the food is in the intestinal mucosa with palmitic acid ( Palmitic acid) is combined with palmitic acid retinoic acid and incorporated into chylomicrons. It is rotated by lymphatic vessels and taken up and stored by the liver. It is hydrolyzed into free retinol by the body and is a specific transporter in plasma. Retinol binding protein (RBP) and before Protein binding and transport to other tissues, vitamin A and carotene are relatively stable compounds, heat, acid, alkali, insoluble in water, stable in oil, less affected by general cooking process, vitamin C, E Antioxidants may be strong enough.

The main functions of vitamin A are: 1 constitute a photosensitive substance in the visual cells, maintaining the visual function under dark light. The rod cells in the human retina contain the photosensitive substance rhodopsin, which is composed of 11-cis retinal. (11-cisretinol) and opsin (opsin) combined, is a necessary substance under the dark light, this combination is a continuous reaction, requires enzymes and energy, there is only one retinal molecule in a rhodopsin molecule, After the light purple, the 11-cis retinal becomes all-in-retinal (alltians-retinol), which cannot be combined with opsin and separated from it. This process is called bleaching. In the dark, the object cannot be seen. After a series of chemical reactions, it becomes 11-cis retinal, and then recombines with opsin to form rhodopsin. It is a weak light substance. When the synthesis is reduced, the human body is weakly sensitive. The sensitivity is reduced, the dark adaptation is weakened, and severe night blindness occurs. The purple pigment needs to be continuously regenerated and updated, so it is necessary to continuously supplement vitamin A to maintain the ability to adapt to darkness. 2 Maintain cell membrane stability and maintain the integrity of skin and mucosal epithelial cells. And sound; 3 Into the normal growth of bones and teeth; enhance immune function and disease resistance barrier system; to maintain the normal function of the reproductive system; - erythrocyte porphyrin carotenoids reduce light sensitivity disease in children, so that symptoms.

When vitamin A is deficient, the above physiological processes cannot be performed normally, resulting in a series of clinical manifestations.

The main pathological changes of vitamin A deficiency are epithelial cell changes, which are preceded by atrophy. Following the proliferative response, the original cubic or columnar epithelium is metamorphosed into a stratified squamous epithelium with excessive keratinization and easy desquamation. The epithelial tissues of each part are not deformed at the same time, and the degree of deformation is different. Generally, the lesions of the conjunctiva and cornea are most prominent, followed by the respiratory tract, lacrimal gland, parotid gland, esophageal mucosa, pancreatic duct, urinary and reproductive system epithelial cells. When the skin is hyperkeratotic, the sebaceous glands and sweat glands are atrophied. After treatment, the above pathological changes gradually disappear.

Vitamin A deficiency prevention

Mainly for the supply of vitamin A in children, the method of supply varies according to age.

(1) A large amount of food containing vitamin A should be supplied to pregnant women during the fetal period.

(2) During the baby period, it is necessary to pay attention to human milk feeding. It is necessary to give fat-containing milk, bean food, carrot puree, egg yolk, etc. In addition, spinach soup, tomato juice, etc. can be added. The ability of immature children to absorb fat and vitamin A is weak. It is advisable to give concentrated vitamin A early, but in the application of concentrated Lu, avoid excessive poisoning. In infants, vitamin A 1500-2000 international units (IU, vitamin A1 IU equivalent to retinol 0.3 g, retinol 1 g) It is equivalent to 6 g of carotene].

(3) Larger children have been able to eat a variety of foods. The supply of vitamin A is generally not insufficient. Children need 2000 to 4500 IU. The absorption of chronic diseases is reduced. When consumption is increased, 3,000 to 5,000 IU per day can be given. However, attention should be paid to timely reduction, such as exceeding the required amount, which can cause chronic poisoning over time.

Prevention of vitamin A deficiency not only prevents night blindness, dry eye disease, avoids blindness, but also allows children to develop normally, and the chance of infection in various epithelial tissues can be reduced.

For areas with poor border areas and more common in the blind, it is necessary to pay attention to three aspects of work: 1 to promote the relationship between vitamin A supply and blind disease; 2 to prevent diarrhea and measles; 3 to pay attention to daily intake of vitamin A.

Vitamin A deficiency complications Complications, pediatric dystrophy, weight loss, corneal softening

Systemic symptoms of vitamin A deficiency such as weight loss, dry skin, loss of elasticity, hoarseness, etc., such as concurrent infections develop into full ocular inflammation, eventually blind.

Vitamin A deficiency symptoms Common symptoms Night blind dry skin Dry skin and conjunctival dry spots "chicken blind" or "bird blind" Weak eyes dry scars form dysentery dry spots

1. The earliest symptoms of ocular symptoms are unclear vision in the dark environment, difficulty in orientation, and night blindness. If not carefully examined, it is easy to ignore. After several weeks to several months, the conjunctiva and cornea gradually lose their luster and are slightly exposed in the air. Dry abnormalities, especially the conjunctiva on both sides of the cornea, the earliest changes, dry and wrinkled, keratinous epithelium gradually ruled, forming a white spot shaped like a foam, called the conjunctival dry spot, also known as Bieder's patch, At this time, the lacrimal gland epithelial cells are degenerated, the secretion of tears is reduced, and the epithelial cells of the lacrimal duct are occluded, the tears are less, the child is photophobic, the eye dryness is uncomfortable, the eye is painful, there is a feeling of rolling, often blinking, or by hand, easy to cause secondary infection, corneal gradual dryness, turbidity, white sputum and softening, disease progression, corneal ulceration, necrosis, perforation, extra-irisal and corneal scar formation within a few days to weeks, and finally Until blindness, the retina also has lesions, the fundus is dry, the two eyes are generally sick at the same time, sometimes both eyes have a disease, unilateral onset only occasionally, although the eye symptoms are mostly Several diseases appear earlier, but the eye symptoms of older children often appear after other symptoms.

2, the skin shows dry skin, keratinized hyperplasia, desquamation, keratinized in the hair follicle cavity, and protrudes from the epidermis, so there is a goose bump or coarse sand-like feeling when touching, the most prominent on the extremities and shoulders of the extremities, 4 Infants under the age of the child rarely see this symptom. In addition, there are nails with multiple lines, tarnishing, creases, and hair that is easy to fall off.

3, other manifestations due to vitamin A deficiency, respiratory and urinary tract epithelial proliferation and keratinization, and decreased immune function, easy to cause secondary respiratory infections and pyuria, tongue taste buds due to epithelial keratosis loss of taste function, affect appetite, and some children There may be vomiting, physical development retardation can be seen in infants and young children, severe anemia is caused by poor blood cell formation in the absence of vitamin A. Treatment with adequate iron can not correct anemia. It has been reported that small infants can develop sputum milk and add symptomatic control after vitamin A.

Vitamin A deficiency check

1. Determination of plasma vitamin A content: normal is 300 ~ 500g / L, less than 200g / L is abnormal.

2. Urine examination: counting epithelial cells, such as more than 3 epithelial cells per cubic millimeter (except urinary tract infection) is helpful for diagnosis.

3. Plasma retinal binding protein (RBP) assay: it can reflect the level of vitamin A, normal 40 ~ 50mg / L, children 23.1mg / L.

4. Determination of physiological blind spots: Physiological blind spots are a more sensitive indicator for judging the nutritional status of vitamin A. In the absence of physiological blind spots, the blind spots are reduced after treatment, and visual acuity returns to normal.

5. Retinal current map: The threshold changes and the b-wave becomes smaller.

6. Dark adaptation measurement: Goldman-Weekers dark adaptation meter, Feldman dark adaptation meter or YA-Z type dark adaptation meter can be used. The lack of dark adaptation ability is reduced, and the pupil is slow to respond to light.

7. Conjunctival impression cytology to understand the extent of conjunctival goblet cell density reduction.

Diagnosis and identification of vitamin A deficiency

diagnosis

Eyes with obvious symptoms, combined with feeding history, chronic digestive system or history of wasting disease, diagnosis is not difficult, because of vitamin A deficiency often have complications, so all malnutrition, chronic diarrhea, chronic diarrhea, or measles long-term bogey Mouth, children with photophobia, blind eyes should be carefully examined, the elderly should pay attention to changes in the skin, early and atypical cases, the eye changes are light, especially in infants and young children is easy to ignore, suspicious cases Can do the following checks to help diagnose: 1 with a small cotton swab physiological saline, gently scrape a little substance from the conjunctival surface, visible keratinocytes under the microscope; 2 serum vitamin A determination is the most reliable indicator, Normal children's serum vitamin A value is generally 300 ~ 500g / L, when the deficiency is reduced to 200g / L or even 100g / L; 3 take fresh mid-stage urine about 10mg plus 1% gentian violet solution, shake, For epithelial cell counts, there are up to 3 skin cells per cubic millimeter of normal urine; more than 3 or more, in addition to urinary tract inflammation, can indicate vitamin A deficiency, and urine sediments can be detected by high power microscope. The extent of epithelial keratinosis.

If the food is lack of vitamin A or has malabsorption, symptoms may appear within a few weeks. Infants with congenital biliary obstruction, infantile hepatitis syndrome, and if pneumonia may occur in a short period of time, dry eye should be noticed.

Differential diagnosis

1. Identification with keratoconjunctivitis.

(1) The surface of the conjunctiva is dry, dull and dull, easy to wrinkle, even as thick as the skin, the conjunctival blood vessels are blue, the cornea is dry and turbid, and the perception is slow.

(2) Consciously dry eyes, burning, severe vision loss.

(3) Adults are more common.

2. Other causes of night blindness, such as retinitis pigmentation, must be ruled out, secondary infection can make corneal changes worse, the therapeutic dose of vitamin A can help diagnose.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.