Журнал «Здоровье ребенка» 8 (51) 2013

Cystic fibrosis (CF) is inherited monogenic disorder that affects most critically the lungs and digestive system. Pancreatic insufficiency and diminished bile acid pool cause malabsorption of fat-soluble vitamins A, D, E and K. Deficiency and excess of these nutrients may contribute to the emergence of a large number of pathological conditions and exacerbate disease. Therefore, in the protocols of all European Cystic Fibrosis centers are recommended annually to determine the levels of vitamin A in patients followed by individual dose adjustment.

The term «vitamin A» includes the retinoid family, which includes retinol, dehydro-retinol, retinal and retinoic acid. Vitamin A enters the body with food in the form of retinol (animal products) and carotenoid (plant foods). Despite the large number of sources of vitamin A and its total content in food is not sufficient to physiological needs. Therefore, experts recommend prophylactic use of vitamins.

Ingested retinoids transported into enterocytes and hydrolyzing with various enzymes. Then retinol forms esters as components of chylomicrons are transported from the walls of the intestine into the lymphatic system and the thoracic duct to enter the circulatory system, and then direct to the liver. Most of it goes to the hepatocytes. Next retinol enters the endoplasmic reticulum, where a large number of contained retinol binding protein (RBP). Vitamin A intoxication occurs when retinol in plasma membranes occurs and is not in conjunction with RBP. Hepatocytes synthesize complex retinol-RBP and stellate cells absorb it. Normal reserves of vitamin A in stellate cells can provide the body with vitamins for a few months. They control the mobilization of retinol and maintain its concentration in normal ranges, irrespective of its flow into the body.

Lack of vitamin A can lead to specific eye and skin problems. It is associated with growth retardation, low nutritional status and oxidative stress. Excess of vitamin A can cause respiratory problems, bone lesions and lead to liver abnormality.

In the international system (SI) levels of micronutrients are measured in mg/dL (for vitamin A 1 mg/dL is equal 0.0349 mmol/l). Normal ranges of retinol plasma are 20–72 g/dL for children and adults and for newborns — 13–50 mg/dL.

Serum retinol deficiency understood better than its excess. Deficiency of vitamin A is defined when serum retinol is below 0.35 mmol/l.

Indications for supplementation vitamin A are the prevention and treatment of hypo- and avitaminosis. Prophylactic doses determined according to the daily needs of the human body for vitamins. The use of vitamin A in therapeutic doses should be done under medical supervision required.

For patients with CF, according to the protocol of the European countries, there are daily prophylactic doses of vitamin A (Table 1).