In the clinic, parents often ask whether their children need calcium supplements, and even worry that calcium deficiency may lead to “rickets”. How long does it take to supplement? Calcium is an important mineral in the body, involved in bone development, muscle contraction, nerve conduction, hormone release and other important physiological functions. Therefore, children need to get enough calcium every day to ensure their healthy growth, so it can be said that “calcium supplementation” is a lifelong task. However, the recommended way to take calcium supplements is to get enough calcium from food (such as milk and various dairy products) every day, not from calcium supplements, which can cause many side effects. Therefore, it is not recommended to take a mixture of calcium and vitamin D preparations unless in certain disease states and except on the advice of a doctor. The important role of vitamin D is to promote the body’s absorption of calcium, simply put, no matter how much calcium we supplement, without the help of vitamin D, it may lead to the body in a state of calcium deficiency. Parents often struggle not to supplement calcium will not get rickets, in fact, the full name of rickets is “vitamin D deficiency rickets”, is due to vitamin D deficiency resulting in calcium malabsorption and abnormal bone development. The source of vitamin D can be obtained from food and sunlight exposure, but there are very few foods rich in vitamin D (mainly cod liver oil), and with the increased awareness of sun protection, it is not recommended that children receive ultraviolet radiation for too long, so there may be a vitamin D deficiency, and vitamin D supplements are needed. The following cases require vitamin D supplements : 1, exclusive breastfeeding and mixed feeding babies, starting 2 weeks after birth to supplement 400IU vitamin D per day; 2, formula feeding and older children who consume less than 900ml of formula or milk with added vitamin D per day, need to supplement 400IU vitamin D per day; 3, adolescent children need to supplement when they cannot get 400IU vitamin D from food; 4, due to suffering from some special Children with vitamin D deficiency due to some special diseases need additional vitamin D supplementation under doctor’s advice. In addition, children aged 9 to 18 years need more calcium to promote development and to prevent osteoporosis in adulthood. 60% of boys and 80% of girls in this period cannot get enough calcium and vitamin D from food and need calcium and vitamin D supplementation.