Long-term consumption of vitamin A or carotene, the skin will turn yellow.

Vitamin A has a variety of physiological functions to promote growth, reproduction, maintenance of bones, epithelial tissues, vision and normal secretion of mucosal epithelium, etc. Vitamin A and its analogs have the role of preventing precancerous lesions. Deficiency is manifested as growth retardation, dark adaptation ability is reduced and the formation of night blindness.

Because of the epidermis and mucous membrane epithelial cell dryness, desquamation, hyperkeratosis, lacrimal gland secretion is reduced, thus dry eye disease occurs, and in severe cases, the cornea is softened, perforation and blindness.

The respiratory epithelial cells are keratinized and lose their cilia, reducing resistance to infection. China's adult vitamin A recommended intake (RNI) for men 800ug retinol activity equivalent per day, women 700ug retinol activity equivalent per day.