Excessive intake of vitamin A can cause acute or chronic poisoning. Acute poisoning in children is caused by ingesting large doses of vitamin A (>100,000 μg or 300,000 IU), manifested by increased intracranial pressure and vomiting, which can lead to death unless intake is stopped. Recovery is spontaneous without residual damage; only two deaths have been reported. Arctic explorers, after consuming the livers of polar bears or seals containing millions of units of vitamin A, developed drowsiness, dysphoria, headache, and vomiting within hours, followed by skin peeling. Large-dose vitamin A tablets, if taken long-term, can also occasionally cause acute poisoning.

Chronic poisoning in older children and adults usually occurs after daily doses exceeding 33,000 μg (100,000 IU) for several months. Infants may show signs of poisoning within weeks if given 6,000–20,000 μg (20,000–60,000 IU) of water-soluble vitamin A daily. There are reports of birth defects in children born to women who received 13-cis-vitamin A (isotretinoin) for skin diseases during pregnancy.

Patients with nodular acne who take large daily doses (50,000–120,000 μg or 150,000–350,000 IU) of vitamin A or its metabolites, although the treatment is effective, are at risk of vitamin A poisoning.

Although carotene is metabolized into vitamin A at a slow rate in the body, excessive carotene intake does not cause vitamin A poisoning but leads to carotenemia (carotene blood levels >250 μg/dL (>4.65 μmol/L)), which is usually asymptomatic but can cause carotenoderma, where the skin (but not the sclera) turns deep yellow, especially on the palms and soles. Carotenoderma can also occur in diabetes, myxedema, and anorexia nervosa, likely due to a further reduced rate of carotene conversion to vitamin A.

The hair is sparse and coarse, the eyebrows fall out, the skin is dry and rough, and the lips have rhagades, all of which are early signs. Subsequently, severe headaches, pseudotumor cerebri, and generalized weakness may occur. Cortical bone thickening and arthralgia are quite common, especially in children, and hepatosplenomegaly may also appear.

The normal fasting plasma vitamin A concentration ranges from 20~80μg/dl (0.7~2.8μmol/l). In vitamin A toxicity, the fasting plasma concentration may exceed 100μg/dl (3.49μmol/l), with some cases reaching as high as 2000μg/dl (69.8μmol/l). Differential diagnosis can be challenging due to the diverse and bizarre symptoms, but it typically includes headaches and skin rashes.

bubble_chart Prognosis

The prognosis for both adults and children is excellent. Symptoms and signs typically disappear within 1 to 4 weeks after discontinuing vitamin A intake. However, the prognosis remains guarded for fetuses whose mothers have taken high doses of vitamin A.