There are three active forms of vitamin A: retinol, retinal and retinoic acid. Vitamin A deficiency is the main preventable cause of blindness worldwide and the primary cause of childhood morbidity and mortality in the developing world.
Maternal vitamin A deficiency during pregnancy is associated with high rates of maternal and infant mortality and with a significant risk of premature birth, miscarriage or fetal death. Both deficiency and hypervitaminosis A during pregnancy are associated with congenital malformations, but the teratogenic effect was described only for a daily intake of more toxic fat soluble vitamins 10, IU of toxic fat soluble vitamins vitamin A supplements.
- Mancare detoxifiere
- Vitamina A în sarcină
In conclusion, vitamin A supplementation is recommended only for pregnant women from areas with endemic avitaminosis A, in order to prevent nyctalopia.
Keywords retinol, retinoic acid, congenital malformations, vitamin A deficiency, teratogenesis, hypervitaminosis Rezumat Vitamina A face parte din categoria vitaminelor liposolubile care, pe lângă funcţiile exercitate la nivel sistemic, joacă un rol important în cadrul organogenezei.
Vitamina A se prezintă sub trei forme active: retinol, retinal şi acid retinoic.
Deficitul de vitamină A este nu numai principala cauză prevenibilă de orbire la nivel mondial, dar şi un factor etiopatogenic esenţial în ceea ce priveşte morbiditatea şi mortalitatea virus papiloma en hombres tratamiento în ţările în curs de dezvoltare.
Deficitul matern de vitamină A în timpul sarcinii se asociază cu rate mari ale mortalităţii materne şi infantile, dar şi cu un risc semnificativ de naştere prematură, avort sau moarte fetală.
Atât deficitul, cât şi hipervitaminoza A pe parcursul sarcinii sunt asociate cu apariţia malformaţiilor congenitale, însă efectul teratogen este descris doar în cazul unui aport zilnic de peste În concluzie, suplimentarea cu vitamină A este recomandată doar în cazul femeilor gravide din zone cu deficit endemic de vitamină A, cu scopul prevenţiei nictalopiei.
Cuvinte cheie retinol acid retinoic malformaţii congenitale deficit de vitamină A teratogeneză hipervitaminoză Introduction Vitamin A is an essential nutrient and a fat-soluble vitamin which performs a lot of systemic functions.
Adequate vitamin A is required for erythrocyte production, tissue differentiation, normal development of bones and teeth, immune competence, reproduction, proper gastrointestinal activity and vision.
It also has an important role during the embryonic development, being involved in organogenesis There are two forms of vitamin A: preformed vitamin A retinol and provitamin A carotenoidsbut the three active forms are: retinol, retinal and retinoic acid 3.
While the retinoic acid is responsible for growth and development, the retinol and retinal forms of vitamin A play an essential toxic fat soluble vitamins in maintaining the reproductive functions and the normal vision 4. Carotenoids may be converted to vitamin A in the liver, where they will be ultimately stored 5.
While preformed vitamin A comes from animal sources from the diet liver, milk, eggs, cheesethe carotenoids intake is based on plant sources, consisting of fruits and vegetables spinach, carrots, pumpkins, sweet potatoes 2,3,6,7.
Ai fost blocat(ă) temporar
Taking into account that there is a reduced absorption of vitamin A coming from plant sources, it is quite useful the consumption căzând de pe veruci animal food products, in order to maintain an adequate level of vitamin A 5.
The need of vitamin A is increased during pregnancy because of its essential role in supporting the maternal metabolism and the fetal development. Among populations with a low prevalence of vitamin A deficiency, it is considered that the hepatic stores are sufficient to ensure the daily requirement of this nutrient 5.
On the other hand, in case of an endemic vitamin A deficiency, it is recommended daily or weekly supplementation, in order to prevent nyctalopia 8. Avitaminosis A is a severe public health problem in many geographical regions, being considered the main preventable cause of blindness 1. It is estimated that vitamin A deficiency leads to blindness in million children worldwide, half of these children dying within a year of vision loss 7.
- Vitaminele sunt compuși organici care sunt necesari metabolismului corpului și, în general, trebuie să fie furnizați din dietă.
- Metode detoxifiere colon
- An investigation of the potential influences of As, Hg, Tl and Pb on Se metabolism, which can suggest new drugs to cope the poisonousness of Se.
- Poze negi pe fata
- Tratamentul preventiv al paraziților
It is also a predisposing factor for multiple comorbidities, such as: respiratory diseases, measles, diarrhea, anemia, convulsive cough, thyroid dysfunction, some dermatological lesions, and moderate-severe forms of malnutrition in children 1,9,3. Thus, vitamin A deficiency is the primary cause of childhood morbidity and mortality in the developing world, especially in Africa and Southeast Asia 7.
Maternal vitamin A deficiency during pregnancy is associated with high rates of maternal and infant mortality and with a significant risk of miscarriage, fetal death or premature birth 9, Hpv genital warts cause throat cancer an adequate and balanced diet in pregnancy has an essential role in the prevention of avitaminosis A, since the toxicity of vitamin A is often described in case of dietary supplements intake, especially for those with preformed vitamin A 5.
Vitamin A deficiency can result in malnutrition and inflammation, affecting growth, development and functional outcomes. It has an essential role for the maintenance of vertebral identity, the prevention of malformations and for the development of skeletal elements during embryogenesis 4.
It is associated with numerous factors, such as: low educational and socioeconomic status, unhealthy lifestyle during pregnancy consisting in smoking and alcohol consumption, as well as an advanced gestational age. The avitaminosis A is owing to an inadequate intake of preformed vitamin A from animal food sources or carotenoids from fruits and vegetables 3.
Subclinical vitamin A deficiency is defined by serum retinol concentrations below 0. Some studies have shown that the serum level of retinol can be used as a predictive factor for preeclampsia, being reported low concentrations of plasma retinol in pregnant women with preeclampsia and eclampsia.
However, the role of vitamin A in the etiopathology of pregnancy-induced hypertension is not completely known 9. Maternal deficiency of vitamin A during pregnancy is associated with high rates of maternal and infant mortality in the first year of life Also, subclinical deficiency of vitamin A in the third trimester of pregnancy increases the risk of preterm birth and maternal anemia 9.
Thus, there is recommended the vitamin A supplementation in pregnant women with a low socioeconomic status, avitaminosis A being associated not only with an 1.
Vitamina - Vitaminele liposolubile
The mechanisms of anemia occurrence are related to some of the effects of vitamin A, including: anti-infectious role, the modulation of iron metabolism, and the increase of circulating level of erythropoietin 9. More than half of pregnant women with vitamin A deficiency have nyctalopia, with a higher prevalence during the third trimester of pregnancy, because of the acceleration of fetal growth 3, Nyctalopia is one of the first clinical manifestations of vitamin A deficiency, along with conjunctival xerosis and Bitot spots keratin debris in the conjunctivasubsequently leading, in case of a severe and prolonged vitamin A deficiency, to corneal scars, keratomalacia drying and clouding of the cornea with ulceration and permanent blindness.
Vitamin A acetate stock solution Soluția stoc de vitamină A acetat eurlex-diff The nominal concentration of this diluted working standard solution is 56 IU vitamin A per ml. Concentrația nominală a acestei soluții etalon de lucru diluate este de 56 UI de vitamină A per ml. Concentrația nominală a acestei soluții este de 6,72 UI de vitamină A per ml. EurLex-2 Vitamin A includes all-trans-retinyl alcohol and its cis-isomers which are determined by this method. Vitamina A include alcoolul all-trans-retinil și izomerii săi cis, care se determină prin această metodă.
Another specific ocular manifestation owing to avitaminosis A is xerophthalmia dry eyes and failure to produce tears 2,3,21, Taking into account that half of children with blindness due to vitamin A deficiency are dying toxic fat soluble vitamins one year from the occurrence of blindness, promoting vitamin A supplementation in endemic deficit areas is an important public health method which reduces the infant mortality 13,23, Vitamin A deficiency is a major cause of childhood morbidity and mortality, being associated with severe immunodepression, which predisposes to a high incidence of respiratory infections and other infectious diseases, such as diarrhea and measles 3, In children with avitaminosis A, measles is a predisposing factor for conjunctival and corneal affliction, this being associated with higher mortality rate compared with cases of measles among children with normal vitamin A status 3,25, Some studies showed that vitamin A deficiency in mothers with HIV infection is associated with a fold increased rate of mother-to-child transmission 3,16, However, other studies including pregnant women and women during breastfeeding have not shown significant benefits of vitamin A supplementation on the rate of transmission of HIV infection from mother to child 3, A study which included children with combined iodine and vitamin A deficiency has demonstrated increased thyroid hormone and TSH concentrations, as well as an increased risk of goiter, related to the severity of vitamin A deficiency 3, Even without supplementation of iodine deficiency, vitamin A administration led to reduced TSH and thyreoglobulin concentrations, as well as a decrease in thyroid gland volume 3, It has been shown that vitamin A deficiency in pregnant women interacts with iron deficiency, which is another major micronutrient.
This can be explained not only by the role of vitamin A in supporting the mobilization and the transport of iron, but also by its importance in hematopoiesis, a process requiring large amounts of iron. In addition, it was found that simultaneous use of vitamin A and iron supplements is more effective in preventing the iron deficiency anemia than the use of either of these nutrients alone 4.
Vitamin A in pregnancy
Vitamin A deficiency is also associated with other conditions, including follicular hyperkeratosis, characterized by excessive keratin synthesis in the hair follicles, with initial localization at the extremities, but with the possibility of generalization 3,31, Another symptom of vitamin A deficiency is bronchopulmonary dysplasia, which is a form of chronic disease with an unfavorable prognosis, occurring in toxic fat soluble vitamins one third of preterm infants less than 28 weeks of gestation.
It has been shown that intramuscular administration of IU of vitamin A three times per week during four weeks in preterm infants has been associated with a significant reduction in the risk of developing bronchopulmonary dysplasia 3,32, Animal studies have shown that severe vitamin A deficiency in pregnancy induces abortion, fetal death and fetal birth defects, mostly consisting in microphthalmia, anophthalmia and abnormalities of the lung, cardiac and urogenital systems. There have also been reported facial, renal and diaphragmatic malformations, along with severe enamel and dentin dysplasia.
Other animal studies have been found a relationship between the maternal vitamin A deficiency and the occurrence of ocular defects, such as: coloboma, penetration of the retina by mesodermal tissue, retinal eversion, defects in the iris and low insertion of the optic stalk Subsequently, human studies have also demonstrated a direct relationship between maternal vitamin A deficiency during pregnancy and the development of congenital ocular defects 4,10,12, Hypervitaminosis A in pregnancy and teratogenesis Although vitamin A supplementation during pregnancy can have many benefits, it has been shown that a daily intake of more than 10, IU of preformed vitamin A derived from supplements toxic fat soluble vitamins associated with the occurrence of congenital defects in 1 of 57 children.
The teratogenic risk is correlated with the intake of high doses of vitamin A before the 17th week toxic fat soluble vitamins gestation.
In addition, the congenital defects were mainly observed in the tissues derived from neural crest cells.