Vitamin is an essential nutrient to maintain the normal life activity of human body. When there is a lack of vitamin, it will cause the failure of material metabolism in human body, and even will lead to diseases, and this is called as "vitamin deficiency". Human body only needs very small amount of vitamins, however, most of the vitamins can not be synthesized in the body, but must be supplied by foods. There are many kinds of vitamins. In terms of dissolubility, vitamins can be classified into two major categories: fat-soluble and water-soluble. In detail, there are the following main kinds:

First,
It is also known as retinene or Carotene. It is mainly from animal liver, egg yolks, dairy products, as well as carrots, green leafy vegetables, red peppers, apricots, persimmons and so on. Carotene can change into vitamin A in the body. Vitamin A can maintain the normal vision, protect the epithelial cells, increase the resistance against infectious diseases, and promote growth and development of the body. When there is a lack vitamin A, it will cause symptoms such as night blindness, dry skin and slow growth.

Second, vitamin D
The content of vitamin D is very high in animal liver, cod liver oil and eggs. The major role of vitamin D is to adjust the metabolism of calcium and phosphorus, and promote the absorption of them. Lack of vitamin D will weaken the ability of the intestinal tract to absorb calcium and phosphorus, and will lead to osteomalacia and affect dental calcification. It will cause rickets disease on the children and osteomalacia on the adults.

Third, vitamin B1
It is also known as thiamine. A lot of foods are rich in thiamine, such as grains, yeast, beans, lean meat, eggs and animal heart, liver, kidney, brain and so on. Lack of vitamin B1 will affect the appetite, cause beriberi, polyneuritis, edema, and even heart failure.

Fourth, vitamin B2
It is also known as riboflavin. Vitamin B2 is very rich in the animal foods, such as liver, kidney, milk and so on. Lack of vitamin B2 will cause ulcers, cheilitis, glossitis, keratitis, seborrheic dermatitis, and scrotal dermatitis.

Fifth, vitamin C
Also known as ascorbic acid, vitamin C is an essential substance for the metabolism of the body. It can maintain the normal function of the teeth, bones and the muscle of blood vessels. What's more, it can enhance the immunity against the disease of the body, promote wound healing, as well as prevent cancer. Vitamin C is very abundant in fresh vegetables and fruits, especially green leafy vegetables. Lack of vitamin C will lead to scurvy.