Vitamin A can cause toxicity if used incorrectly.

Vitamin A (also known as retinol) is an essential nutrient for humans and belongs to the group of fat-soluble vitamins. In some animal-derived foods, the primary form of vitamin A is retinol, but it can also exist as retinal or retinoic acid.

A persistent vitamin A deficiency leads to a series of changes, the most destructive of which occur in the eyes. These visual changes are collectively known as xerophthalmia. First, the conjunctiva dries out due to the replacement of the epithelium of the tear and mucous glands with keratinized epithelium. Next, keratin debris accumulates into small, translucent plaques, and finally, the rough surface of the cornea erodes, leading to corneal degeneration and destruction, and complete blindness. Therefore, vitamin A is indicated for the treatment of conditions such as xerophthalmia, night blindness, stunted growth in children, increased susceptibility to respiratory infections, acne, dry and brittle skin, hair, and nails, and for promoting wound and burn healing.

Because vitamin A is fat-soluble, it is more difficult to eliminate excess amounts absorbed from food compared to water-soluble vitamins. Therefore, an overdose can lead to vitamin A toxicity. This 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, even 4,000 IU/kg per day can cause significant damage. Excessive alcohol consumption can also increase vitamin A toxicity.

Dry eyes can be caused by vitamin A deficiency.

In chronic cases, hair loss, dry mucous membranes, fever, fatigue, weight loss, fractures, anemia, and diarrhea may be the leading symptoms associated with less severe vitamin A toxicity. These symptoms only occur when taking vitamin A supplements orally. Carotenoids (such as beta-carotene in carrots) do not cause such symptoms. Therefore, obtaining vitamin A through food is safer. A recent study showing a correlation between low bone mineral density and high vitamin A intake also warns that overdosing on this vitamin can cause bone diseases.

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 heavily on the amount of lipids consumed along with food. Therefore, users of this medication should strictly adhere to the prescribed dosage and pay attention to their diet, avoiding fatty foods while taking the medication.

According to Health & Life - MD