Although we all know that vitamin supplements are important, there are always some small key points that are overlooked, such as vitamin A. Vitamin A deficiency in children is one of the four major nutritional diseases in the world. It has been recognized by WHO as one of the four major nutritional deficiencies in the world. Vitamin A deficiency in children in China accounts for 33.4% of the total number. This percentage is even higher in rural areas. What is vitamin on earth? Vitamins are a class of organic substances necessary for the maintenance of normal metabolic function of the human body. They account for a very small portion of the body and can be divided into two categories: fat-soluble vitamins and water-soluble vitamins. Fat-soluble vitamins are a class of organic substances that are insoluble in water, including vitamins A, D and E. Water-soluble vitamins are soluble in water, including vitamins B and vitamin C. Where does vitamin A come from? And where would it go? There are two major sources of vitamin A: one is retinol from animal foods, mainly from milk, eggs, and animal guts. The other one is plant food, which is mainly found in dark vegetables and fruits. Vitamin A will be absorbed by the small intestine and will bind to the chylomicrons. It then enters the bloodstream through the lymphatic system. After transportation, it is stored in the liver. The vitamin A ester in the liver can be hydrolyzed into retinol when needed by the surrounding tissue. It can play a direct role in this form. Beta carotene is a precursor to vitamin A. In the intestinal mucosa of animals, it can be converted into active vitamin A. It is mainly excreted by the kidneys and but a small amount can be excreted by milk. The Role of Vitamin A in Human Body Vitamin A includes: retinol, retinal, retinyl ester and retinoic acid. Among them, retinoic acid is an important active form of vitamin A, which makes vitamin A work. Retinoic acid plays the following functions in the human body: 1. Vitamin A is involved in the formation of photosensitivity matter in visual cells. Lack of it will lead to night blindness. 2. Vitamin A affects the stability and integrity of epithelial cells. Lack of it can cause dryness in skin and the eyes. 3. Vitamin A affects growth and development through the synthesis of DNA and RNA in cells and the secretion of growth hormone. It also affects sperm production and placental development. 4. Vitamin A is involved in the maintenance of immune activity in the body, thereby promoting the production of antibodies by immune cells. 5. Vitamin A deficiency can affect the transport and storage of iron, leading to anemia. The acquisition must be correct and be in an appropriate amount At present, children aged 0-3 years in China are still at high risk of vitamin A deficiency, especially in poor areas. For infants, preschool children and pregnant women, extra vitamin A supplements or foods fortified with vitamin A are needed. It is particularly important to note that when using vegetable vitamin A such as carrots and other vegetables, it is better to cook or fry it in oil to fully absorb vitamin A. To better acquire its nutrition, don't overcook it. New ideas on clinical application of vitamin A With more studies on the role of vitamin A, Amaral CT and other studies have found that children with vitamin A deficiency have a significantly higher incidence of respiratory infections than children with normal vitamin A levels. The incidence of pneumonia and asthma increases with the degree of vitamin A deficiency. Vitamin A supplementation can effectively reduce the incidence of respiratory tract infection in children with vitamin A deficiency . For iron deficiency anemia, there are also experimental comparisons found that the recovery rate of symptoms in children treated with ferrous sulfate combined with vitamin A was significantly higher than that in children treated only with ferrous sulfate. The final reminder is that although vitamin A deficiency causes many diseases, overdose can also be harmful to the health. Because vitamin A is insoluble in water, if it is not properly supplemented, it will lead to excessive vitamin A poisoning, causing damage to skin, bones, brain, liver and other organs. Therefore, vitamin A should be supplemented and taken under the guidance of a doctor. References:  Ji Xin, Gao Junfang, Zhang Fang, Hu Chuanxin, Shu Fangfang. Therapeutic Effect of Vitamin A on Children with Recurrent Respiratory Tract Infection Complicated with Anemia [J]. Chinese Journal of Nosocomiology, 2019, 29 (10): 1557-1561.  Wang Zhixu. Vitamin A [A]. Chinese Nutrition Society. Proceedings of the Second Symposium on Reference Intake of Dietary Nutrients of Chinese Nutrition Society [C]. Chinese Nutrition Society: Chinese Nutrition Society, 2011: 26. Amaral CT,Pontes NN,Maciel BL,et al. Vitamin A deficiency alters airway resistance in children with acute upper respiratory infection[J].Pediatric Pulmonology,2013,48(5):481-489.  Jia Xiaohong. Effect of Vitamin A on Iron Deficiency Anemia in Children [J]. Chinese Journal of Practical Medicine, 2015, 10 (31): 182-184.