Sunlight has a variety of effects on human health. For example, sunlight on the skin will cause the subcutaneous blood vessels to expand and blood flow to flourish, which is conducive to the excretion of toxic substances and enhances the skin’s resistance, and will also increase the secretion of saliva and gastric juice and strengthen intestinal peristalsis, thus promoting appetite and digestion. More importantly, the skin is exposed to sunlight to produce vitamin D. We all know that calcium and phosphorus are the main components of bones, and the absorption of calcium must rely on the presence of vitamin D. If there is a lack of vitamin D, calcium cannot be absorbed. If there is a lack of vitamin D, calcium is not absorbed and bones are stunted. We have a lot of exposure to sunlight and often don’t think about how important it is to our health, just as we don’t feel the presence of air when we live in it. Why do children need more sunlight? The reason is simple: the younger the child, the faster he or she develops, and the bones are the frame that supports the weight of the whole body and must keep up with the developmental needs of all parts, but calcium, an important raw material for manufacturing bones, must rely on vitamin D to be absorbed, and the lack of sunlight prevents vitamin D from being synthesized, which is bound to get chondromalacia. Some people think that the sunlight can shine in through the glass windows, but in fact, the window glass only allows some irrelevant light to pass through, and the ultraviolet rays that can create vitamin D are mostly blocked outside the window. If children live in a dark room for a long time, although they also have the same equipment to produce vitamin D a skin, but can not be exposed to sunlight is also in vain. Although vitamin D can be supplied from outside the body, such as cod liver oil, eggs, meat, fresh vegetables contain a lot of vitamin D, but it is not as direct as the body’s own production.