Vitamin A in the human body has many important roles, can maintain vision, bone growth, reproductive function, cell differentiation, cell proliferation, regulate the expression of many genes, can also strengthen the immune system and prevent infection. The main physiological functions are:
1. The maintenance of the epithelial cells of healthy tissue. Epithelial cells are the body's first line of defense of the invasion of foreign matter, and some epithelial cells secrete mucus, keep the skin moist and clean. Vitamin A deficiency epithelial cells and keratinocytes Gan crack, lost defensive function, can not be lubricated by mucus secretion. The eye is most sensitive, dry mucous membranes can cause dry eye syndrome. Other mouth, throat, trachea, urinary tract, reproductive tract and intestinal mucosa will atrophy and horny, the respiratory, digestive, reproductive health, such as loss of function.
2. Maintain normal visual effect. Photoreceptor cells in the retina of the eye contains which columnar cells containing "visual purple" in the light is weak, is responsible for receiving light stimulation to produce vision. Vitamin A is a component of rhodopsin, the absence of influence rhodopsin regeneration, low light vision can not be quickly restored, is night blindness. 3. To strengthen immune function, resistance to bacterial and viral infections. Vaccination is not popular in the region, children suffering from measles if vitamin A, can reduce mortality. Vitamin A can maintain the proliferation and cytokine secretion of T cells of the immune function.
4. ensure the normal development and growth of the embryo. Early embryonic development, cell proliferation and differentiation according to the time required to different organizations, the role of these genes in a timely and need the right amount of performance, these adjustments are very precise and disorders can cause deformities. Vitamin A developmental patterns of genes involved in the regulation. Vitamin A is a generic term that includes all direct or indirect provision of vitamin A active ingredient. Food ingredients that have vitamin A activity has two kinds of animal and vegetable sources. People daily intake of vitamin A to about 60% from vegetables.
The main ingredients of animal vitamin A is "retinol", after use can be directly absorbed by the body, which is the most active form. Food sources with cod liver oil, liver, egg yolks, whole milk is the most abundant; not much meat content in general. Note that retinol can cause excessive toxicity, the most serious consequence of this is embryonic malformations, pregnant women must be careful not too much to