Vitamin A
Vitamin A or Retinol plays important role in the function retinal vision, growth, reproduction, embryonic development as well as in immune function. Vitamin A is also required for adaptive immunity and plays a role in the development of both T- helper cells and B-cells. Retinol and its metabolites and synthetic retinoids provide protective effects against the development of certain types of cancer by blocking tumor promotion, by inhibiting proliferation, by inducing apoptosis, by inducing differentiation or by performing combination of these actions. Fat malabsorption, particularly caused by celiac disease or chronic pancreatitis and protein -energy malnutrition predisposes to vitamin A deficiency. Clinical features of vitamin A deficiency include degenerative changes in eyes and skin and poor dark adaptation or night blindness. Vitamin A deficiency impairs innate immunity by impeding normal regeneration of mucosal barriers damaged by infection and by diminishing the function of neutrophils, macrophages, and natural killer cells. Toxic effects of hypervitaminosis A have occurred because of ingestion of excess vitamin or as a side effect of inappropriate therapy. Symptoms of acute toxicity from single massive dose present as abdominal pain, nausea, vomiting, severe headache, dizziness, sluggishness and irritability. Chronic toxicity shows symptoms like bone, join pain, hair loss, dryness and fissures of the lips, anorexia, benign intracranial hypertension, weight loss an hepatomegaly.
