Excessive intake of vitamin A can cause a toxic syndrome known as vitamin A toxicity. The earliest reports date back to the 1590s, when Arctic explorers experienced symptoms such as headache, vomiting, and drowsiness hours after consuming polar bear liver, as 90–95% of vitamin A in humans and animals is stored in the liver. In recent years, domestic cases of toxicity have increased due to the misuse of vitamin A concentrates. This is primarily attributed to parents lacking knowledge about the proper use of vitamin A, believing that higher doses are better, coupled with insufficient vigilance among medical professionals, which warrants attention.

bubble_chart Clinical Manifestations

Vitamin A toxicity can be divided into the following two types:

1. Acute type Due to individual differences in children's sensitivity to vitamin A and varying liver storage levels of vitamin A, the toxic dose can vary significantly. Generally, an injection of 300,000 IU of vitamin A can induce toxic symptoms within a few days. Manifestations include decreased appetite, dysphoria or drowsiness, vomiting, bulging anterior fontanelle, increased head circumference, cranial suture separation, and optic disc edema. Increased intracranial pressure is common in the acute type, likely due to increased cerebrospinal fluid volume or impaired absorption. If the child shows no signs of nervous system infection but suddenly exhibits symptoms of elevated intracranial pressure, combined with a history of high vitamin A intake and rapid symptom resolution after discontinuing vitamin A, the diagnosis can be confirmed.

2. Chronic type When the daily intake of vitamin A reaches tens of thousands of units—for example, infants consuming 1,500 IU per kilogram of body weight daily—toxic symptoms may develop after several days. Early symptoms include dysphoria, decreased appetite, low-grade fever, profuse sweating, and alopecia areata. Later, typical bone pain symptoms appear, characterized by migratory pain, often accompanied by soft tissue swelling and tenderness without redness or heat, predominantly affecting long bones and limb bones. Due to epiphyseal involvement in long bones, stunted growth may occur. Some cases present with temporal or occipital swelling and pain, which can be misdiagnosed as craniotabes. Symptoms of increased intracranial pressure, such as headache, vomiting, a wide and bulging anterior fontanelle, cranial suture separation, esotropia, ocular tremor, and diplopia, are another hallmark of this condition but are less common than in the acute type. Additionally, symptoms may include pruritus, desquamation, rash, lip rhagades, dry hair, hepatosplenomegaly, abdominal pain, myalgia, bleeding, renal lesions, and hypoplastic anemia with leukopenia. Serum alkaline phosphatase levels are often elevated. Long-term hepatosplenomegaly has been reported abroad to lead to cirrhosis, portal hypertension, and even death.

In addition to the above medical history, symptoms, and signs, X-ray examination has special value in confirming the diagnosis of this disease. It manifests as abnormal tubular bone modeling, bone resorption, fracture; changes in the epiphyseal plate and soft tissue swelling; subperiosteal new bone formation in the diaphysis; widened cranial sutures, and a full, enlarged anterior fontanelle.

The cerebrospinal fluid pressure is increased, reaching up to 2.55 kPa (260 mmH₂O), with cells and glucose within the normal range. Some have found decreased protein or normal to low-normal values. If serum vitamin A is examined, it often exceeds 1000–6000 μg/L.

bubble_chart Treatment Measures

Once vitamin A toxicity is diagnosed, intake should be stopped immediately. Symptoms usually disappear rapidly within 1–2 weeks, but blood vitamin A levels may remain elevated for several months. Skull X-ray findings typically return to normal within 6 weeks to 2 months, while long bone X-ray abnormalities recover more slowly, often taking about half a year. Therefore, vitamin A should be avoided for several months to prevent symptom recurrence. When using concentrated fish liver oil or vitamin A preparations, the dosage must not exceed requirements. If high doses are necessary, the duration of use must be strictly limited to avoid toxicity. Some reports indicate that excessive vitamin A intake during early pregnancy may lead to late abortion and fetal malformations. Thus, pregnant women should not exceed a daily intake of 5,000 IU.

bubble_chart Prevention

Beijing implemented vitamin AD-fortified milk for infant feeding, effectively preventing vitamin A deficiency without any observed symptoms of vitamin A excess.