Vitamin D has an important role in the metabolism of bone and possibly (not sure) in the regulation of immune function. Vitamin D is produced through sun exposure or ingested through fish oil, eggs, and fortified foods. Infants have low vitamin D reserves and obtain it primarily through breastfeeding, sun exposure, or vitamin D supplementation during the first few months. The vitamin D content of breast milk is usually low and sun exposure is usually low at this time, especially at higher latitudes, making them susceptible to vitamin D deficiency, leading to abnormal calcium deposition in the bones (rickets), convulsions, and feeding difficulties. Current clinical evidence suggests that vitamin D supplementation is effective in preventing rickets, especially in infants with low sunlight exposure or dark skin. The WHO above emphasizes the importance of vitamin D supplementation, but is unclear about exactly what should be done. Isn’t this nonsense? Who doesn’t know it’s important, it’s all about what to do! Who needs to supplement First look at the daily requirement of healthy infants (DRI) This data is relatively early, but the daily requirement will not change greatly. You can also check the data published by our country, much the same. Full-term infants: 210 mg of calcium and 200 IU of vitamin D per day for healthy infants aged 0-6 months (based on the daily requirements for infants aged 0-6 months published in North America and in China). Breastfeeding: If an infant consumes 800 ml of milk per day (24 hours), for example, each 100 ml of breast milk contains 2.5 IU of vitamin D and 29 mg of calcium, i.e., 20 IU of vitamin D and 232 mg of calcium per day through breast milk. Calcium supplementation is not required. Full-term formula-fed infants: Each 100 ml of formula milk (a certain brand of milk powder, for example) contains 40 IU of vitamin D and 42 mg of calcium, which is equivalent to a daily intake of 320 IU of vitamin D and 424 mg of calcium through formula milk, which is basically sufficient for vitamin D and adequate for calcium, but the absorption is average. Preterm infants need 150-400 IU of vitamin D and 120-230 mg of calcium per day. According to the above calculation, preterm infants need more vitamin D but the same amount of calcium. Based on this calculation, it can be seen that all breastfed children need vitamin D supplementation, but calcium is basically enough. Formula-fed infants delivered at term do not need vitamin D and calcium supplements, but preterm infants need vitamin D supplements and not calcium supplements. How much to supplement If you follow the calculations above, it is easy to come up with a dose of additional vitamin D that needs to be added. However, mathematical calculations often deviate from reality, so let’s look at the conclusions reached by some clinical studies. Professional studies are the first source of reliable data for doctors, so I’ll try to keep the description as simple as possible. An article published in 2014 in the second issue of Pediatric Research studied 213 exclusively breastfed infants, during the winter and in a study area of 41 degrees north latitude. These infants were given 200, 400, 600 and 800 IU of vitamin D for nine months starting at full term. The study found that healthy infants had low blood levels of vitamin D at full term and that supplementation with all four doses maintained vitamin D levels in the normal range (as shown below, with increasing doses from the bottom up and serum vitamin D above 50 on the y-axis considered normal). The study recommended daily supplementation of 400 IU/day. An article was also published in 2014 in Pediatrics III on preterm infants given 400 or 800 IU/day, respectively, for 48 infants in each group. The evaluation metric was serum vitamin D levels at just 40 weeks of age. It was found that those with 800 IU/day had a lower risk of low vitamin D levels than those with 400 IU, but both had comparable bone mineral density. There was one case of excess vitamin D in those supplemented with 800 IU/day. In summary, I give the following recommendations: for preterm infants who are primarily breastfed, supplementation with at least 400 IU of vitamin D per day, but no calcium, and for term infants, supplementation with at least 200 IU of vitamin D, preferably 400 IU per day, without calcium. For formula, vitamin D and calcium supplementation is not needed if the milk volume is 800-1000 ml or more, but is still recommended if it is less than 800 ml. Since small preterm infants who are breastfed are usually given fortification with 30 IU of vitamin D and 30 mg of calcium per packet, vitamin D supplementation is not needed during full fortification with fortification, but most do not fortify all However, most do not fortify all breast milk, so supplementation is still necessary. When to start and for how long The general recommendation is to start within 2 months of birth. However, as you can see from the chart above, vitamin D deficiency is already present at 1 month, so I recommend starting around 1 month. Premature infants are at higher risk of vitamin D deficiency at birth due to less maternal acquisition, especially those under 32 weeks, and we usually start supplementation 2 weeks after birth (the main consideration is that infants are better able to feed at this time; that earlier study in Pediatrics started at 2 weeks after birth). Since 0-6 months is a period of low outdoor activity, no complementary foods are added, and milk is the main source of vitamin D, supplementation cannot be stopped. 6-12 months is the period when complementary foods are gradually added, but usually the amount of milk is reduced, so supplementation is still recommended. As for after 1 year of age, for full-term infants, vitamin D supplementation is not needed if they consume milk products (usually more than 1000 ml) and have adequate outdoor activities daily, otherwise supplementation is required. What about premature babies? There is advice to still supplement during 1-3 years of age, I don’t have direct evidence yet, but supplementation is recommended. Can it be toxic? Many parents are concerned about this issue. In the first two studies, one case of high serum vitamin D levels was found in the 800 IU/day supplementation group, but many countries use 400 IU daily supplementation for one year and have not found a risk of toxicity.