In existing nutrition textbooks, the main role of vitamin D has been to regulate the metabolism of calcium, thereby maintaining bone health. In addition, the role of vitamin D in improving immunity is also mentioned. However, recent research (from the "21st Century Vitamin D Health New Concept" Symposium hosted by the International Office of Life Sciences China Office and the Chinese Center for Disease Control and Prevention Nutrition and Food Safety) pointed out that in addition to osteoporosis , Dental caries, children rickets and other "classic" vitamin D deficiency diseases, vitamin D deficiency is also associated with the occurrence of a variety of chronic diseases (such as arteriosclerosis, hypertension, coronary heart disease, diabetes, breast cancer, colon cancer, etc.). Although these important and innovative conclusions still require further in-depth research, such as the mechanism by which vitamin D (related to calcium or calcium-independent mechanisms) is used to prevent chronic diseases, but as Professor Chen Junshi, academician of the Chinese Academy of Engineering said , "We need to update our concepts and re-understand the other important role of vitamin D."

　　Because the vitamin D needed by the human body is mainly synthesized by the skin under the sunlight (to be precise, the ultraviolet rays in sunlight) ——Using 7-dehydrocholesterol as the raw material to synthesize vitamin D2, the conclusion that “vitamin D helps prevent many common chronic diseases” provides us with strong evidence that sunlight (or outdoor activities) is preventing The above-mentioned chronic diseases will play an important role-this seems to coincide with our existing experience. Overall, the incidence of chronic diseases in the north (less sunshine) is generally higher than that in the south (more sunshine).

　　Vitamin D is a very special kind of vitamin, so special that it can be regarded as a human hormone: it is produced by the skin, functions in other parts (intestinal tract, bones and kidneys) and regulates (calcium Metabolism). In daily foods, vitamin D is usually very little, so little that it is almost impossible to satisfy the body''s needs through daily foods (it must be mainly synthesized by the skin under sunlight). Fatty fish, mushrooms and other fungi, egg yolks, pig liver, etc. contain more vitamin D-I emphasize again, even if these foods are often eaten, it is difficult to meet the body''s needs for vitamin D! The skin is exposed to sunlight Synthesis is the main source of vitamin D.

　　 Therefore, if there is insufficient sunlight exposure, such as winter (long cold period) in the north and less outdoor activities, it will inevitably lead to vitamin D deficiency. In this case (insufficient sun exposure), pay attention to the intake of foods rich in vitamin D (not enough), while taking fortified foods with added vitamin D or taking safe doses of vitamin D supplements (too much vitamin D can cause Poisoning, adults do not supplement more than 400 international units per day), such as various cod liver oil preparations, multivitamins, etc.