Explain about the Toxicity - fat soluble Vitamin?

Because vitamin A is fat-soluble and can be stored, primarily in the liver, routine  consumption of large amounts of vitamin A over a period of time can result in toxic  symptoms, including liver damage, bone abnormalities and joint pain, alopecia,  headaches, vomiting and skin desquamation. In fact, symptoms that occur due to intakes in excess of those recommended over a prolonged period are referred to as symptoms of hyl7ervitarizinosis. Hypervitaminosis A appears to be due to abnormal transport and distribution of vitamin A and retinoid s caused by over loading of the plasma transport mechanisms. Very high single doses call cause transient acute toxic symptoms that may include bulging fontanel's in infants, headaches in older children and adults, and vomiting, diarrhoea, loss of appetite and irritability in all age groups.  Rarely does toxicity occur from ingestion of food sources of preformed vitamin A.  When this occurs, it usually results from very frequent consumption of liver products.  Toxicity from food sources of provitamin a, chiefly carotenoids, is not reported, except for the cosmetic yellowing of skin.

Most children aged 1-6 years tolerale single oral doses of 60,000 11g (2,00,000 IU)  vitamin A in oil at intervals of 4-6 months without adverse symptoms. Occasionally diarrhoea or vomiting is reported but these symptoms are transient with no lasting sequelae. Older children seldom experience toxic symptoms unless they habitually ingest vitamin A in excess of 7,500 mg (25,000 IU) for prolonged periods of time.  When women take vitamin A at daily levels of more than 7,500 mg (25,000 IU) during the early stages of gestation, foetal anoinalies aid poor reproductive outcomes are reported. Women who are pregnant or might become pregnant should avoid taking. Excessive amounts of vitamin A. A careful review of the latest available information by a WHO Expert Group recommended that daily intakes in excess of 3,000 mg (10.000 IU) or weekly intakes in excess of 7,500 mg (25,000IU) should not be taken at any period during gestation.