We often encounter parents who do not know much about vitamin D. Some of them have imported various kinds of vitamin D supplements from all over the world; some of them have heard others say that they do not need it and it is not good to supplement more; some of them say look at whoever did not supplement vitamin D, but they are growing quite well; others have no concept of vitamin D supplementation and forget about it after a few days when the doctor reminds them to do so. So, does vitamin D need to be supplemented in the end, and how much is appropriate? Let’s discuss with parents today: First of all, let’s understand what is vitamin D. Vitamin D is a fat-soluble vitamin. It is mainly vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). It is well known that vitamin D can regulate bone metabolism, promote calcium absorption and prevent rickets in infants and children. As research progressed, it was found that in addition to its role in promoting bone health, vitamin D is also associated with chronic diseases such as cardiovascular disease, diabetes, metabolic syndrome, malignancy, and depression. Vitamin D is so good, how do I get it? Vitamin D is most abundant in seafood and animal liver, such as cod, halibut and swordfish, as well as livestock liver, eggs and milk. However, in general, vitamin D obtained from food alone is not enough. The good thing is that the human body and most advanced animals have a special function. 7-dehydrocholesterol contained in our epidermis and dermis can be converted into vitamin D by ultraviolet radiation, and this is the main source of vitamin D in the human body. But in the northern cities of autumn and winter where the sun is rarely seen, it is not easy to get a sufficient amount of sunlight. Besides, the light in summer is not always enough. PS: At present, it is not recommended that infants under 6 months of age be exposed to direct sunlight (which increases the chances of skin cancer); children and adolescents should also pay attention to sun protection when participating in outdoor activities. Therefore, it is essential to take the right amount of vitamin D! How to supplement vitamin D? The Chinese Medical Association issued recommendations for vitamin D supplementation in 2008 and 2010: Pregnant mothers: need to eat foods rich in calcium and phosphorus, and for those who have late pregnancy in autumn and winter, it is recommended to supplement vitamin D 400-1000 IU/d. Infants and children: supplement vitamin D 400 IU/d 2 weeks after birth until 2 years old; supplement vitamin D 200 U/d if the daily formula is more than 500 ml; nano milk If there is sufficient milk and outdoor activities in summer for 1-2h/d, vitamin D supplementation is not necessary. Premature, low birth weight, twin babies and other infants: vitamin D supplementation of 800-1000IU/d after birth is recommended, and 400IU/d after 3 months. Others: diarrheal disease, liver and gallbladder disease, chronic kidney disease, and those taking oral rifampin, isoniazid (anti-tuberculosis drug), and anti-epileptic drugs may also have vitamin D deficiency and require appropriate supplementation. How is vitamin D monitored? The current serum 25(OH)D concentration is the gold standard for monitoring blood vitamin D levels. Currently, the appropriate serum 25(OH)D level for children in China is >50 nmol/L. 37.5-50 nmol/L is considered vitamin D deficiency; Q37.5 nmol/L is considered vitamin D deficiency. In addition, children with poor appetite, partial eating, picky eating, recurrent respiratory infections, obesity, chronic diseases, and growth spurts have low blood 25(OH)D concentrations, which is consistent with the results of most children’s vitamin D level surveys in the literature and should be related to a variety of factors such as current air pollution, little outdoor activity, excessive clothing, shading from tall buildings, and disease effects. Therefore, except for the high-risk group that must be supplemented, other children may want to have their blood 25(OH)D concentrations checked first and then be guided by a medical professional to take vitamin D supplements.