Lack of vitamin A mainly leads to five items: 1, decreased dark adaptability, night blindness, dry conjunctiva and Pitt's spot.

Corneal softening perforation leads to blindness;

2. Changes of mucosa and epithelium

;

3. Growth and development are hindered

Susceptible to respiratory tract infection;

4. Taste and smell are weakened, and appetite is reduced;

5, dry hair, rough skin, hair follicle keratinization, memory loss, irritability and insomnia.