The main functions of vitamin A are as follows: ① It is necessary to maintain the health of all epithelial tissues. When lacking, the epithelial tissue is dry, proliferated and hyperkeratinized, and the ability to resist microbial infection is reduced. For example, the secretion of lacrimal gland epithelium stops, which can make cornea and conjunctiva dry, inflame and even soften perforation. When sebaceous glands and sweat glands are keratinized, the skin is dry and prone to hair follicle papules and hair loss.

In addition, these can also be supplemented: carrots, yellow-green vegetables, eggs, yellow fruits, spinach, pea seedlings, red sweet potatoes, green peppers, cod liver oil, animal livers, milk, dairy products and cream.