Vitamin A can cause poisoning if used incorrectly.

Vitamin A (also known as retinol) is an essential fat-soluble vitamin for humans. In some foods of animal origin, the main form of vitamin A is retinol, but it can also exist as retinal or retinoic acid.

Continuous deficiency of vitamin A will produce a series of changes, the most destructive of which occur in the eyes. Visual changes are collectively known as xerophthalmia. The first is the drying of the conjunctiva due to the replacement of the epithelium of the tear and mucus-secreting glands by keratinized epithelium. This is followed by the accumulation of keratin debris into small translucent patches, and finally the erosion of the rough horny membrane surface with degeneration, destruction of the cornea and total blindness. Therefore, vitamin A is indicated for the treatment of diseases such as xerophthalmia, night blindness, slow growth in children, susceptibility to respiratory infections, acne, brittle skin, hair and nails, and for the rapid healing of wounds and burns.

Because vitamin A is fat-soluble, it is more difficult to excrete excess amounts absorbed from the diet than water-soluble vitamins. Therefore, overdose can lead to vitamin A toxicity. It can cause nausea, jaundice, allergic reactions, anorexia, vomiting, blurred vision, headache, muscle damage, lethargy, and mood changes. Acute toxicity generally occurs at doses of 25,000 IU/kg and chronic toxicity occurs at 4,000 IU/kg per day for 6-15 months. However, liver toxicity can occur at levels as low as 15,000 IU/day, with the average toxic dose being 120,000 IU/day. In people with impaired kidney function, 4,000 IU/kg per day can cause significant damage. Heavy alcohol use can also increase vitamin A toxicity.

Dry eyes due to vitamin A deficiency.

In chronic cases, hair loss, dry mucous membranes, fever, fatigue, weight loss, bone fractures, anemia, and diarrhea may be the leading symptoms associated with less severe poisoning. The above symptoms of poisoning only occur when taking vitamin A supplements orally. Carotenoids (such as beta carotene in carrots) do not cause such symptoms. Therefore, vitamin A supplementation through food is safer. A recent study that showed a correlation between low bone mineral density and high vitamin A intake also warned that excessive doses of this vitamin can cause bone disease.

Note that vitamin A dosage is usually expressed in international units (IU) or retinol equivalents (RE), with 1 IU = 0.3 micrograms of retinol. The absorption of provitamin A also depends largely on the amount of lipids ingested with food. Therefore, people taking this medicine need to strictly follow the recommended dosage and pay attention to a fatty diet while taking the medicine.

According to Suckhoe & Doisong - MD