Harm of Vitamin A Excess

The toxic side effects of vitamin A mainly depend on the intake of retinol and retinyl ester, and are related to the physiological and nutritional status of the body. A liver vitamin A concentration of more than 300 mg/g is considered to be excessive and causes a corresponding clinical toxicity. Clinical manifestations of acute vitamin A overdose include severe rashes, headaches, and pseudo-cerebral coma leading to rapid death. Chronic overdose is relatively more common, with clinical manifestations including central nervous system disorders, liver fibrosis, ascites, and skin damage. Recently, it has been reported that bone marrow suppression caused by excessive vitamin A in infants and hypercalcemia caused by excessive chronic vitamin A in adults. Studies have found that oil-based vitamin A or liver-derived vitamin A is only one-tenth the toxicity of hydrated, emulsified and solid retinol supplements.
Teratogenic effects:
Studies have confirmed that 13-cis retinoic acid has teratogenic effects, and it is feared that human vitamin D may be teratogenic in large doses. A large number of animal experiments have confirmed that excessive vitamin A can cause embryo malformation. Epidemiological data suggest that excessive intake of pre-formed vitamin A can cause birth defects. The most sensitive period is the embryogenesis period (early pregnancy). The birth defects caused by excess vitamin A mainly occur in organs that evolved from brain nerves, such as craniofacial malformations, central nervous system malformations (excluding neural tube defects), thyroid and Heart malformation, etc. It is estimated that long-term daily intake of pre-formed vitamin A over 10,000 IU can cause teratogenicity. These birth defects may occur in oral retinol analogs for the treatment of skin diseases. Topical use of vitamin A analogues in early pregnancy leads to little or no risk of growth abnormalities.
Liver damage:
Animal experiments and human experimental data have confirmed that there is a very clear causal relationship between vitamin A excess and liver dysfunction. This is because the liver is the main storage organ of vitamin A and the main target organ of vitamin A toxicity. Hepatic abnormalities caused by excess vitamin A include reversible elevation of liver enzyme activity, liver fibrosis, cirrhosis and death.