With the increasing awareness of people's health, many people have begun to pay attention to supplementing various nutrients. On the internet, many people say that they "don't spend enough time in the sun" and "their bone density is not high enough", so they need to supplement extra vitamin D; But some people also believe that supplementing too much vitamin D can cause harm to the liver. What is the use of vitamin D for the human body? Who needs to supplement vitamin D, and how to scientifically and reasonably supplement vitamin D? With these questions in mind, a reporter from Science and Technology Daily interviewed relevant experts. Lack of vitamin D or causing various diseases Vitamin D is a fat soluble vitamin that plays an important role in the human body. Vitamin D contributes to bone health, and the vitamin D endocrine system can regulate blood calcium balance and maintain normal blood calcium concentration in the body. "Rong Shuang, Director of the Department of Nutrition and Food Hygiene at Wuhan University, Vice Chairman of the Nutrition and Neuroscience Branch of the Chinese Nutrition Society, and Director of the Chinese Nutrition Society, told reporters. Vitamin D also participates in the regulation of various functions in the body. Rong Shuang stated that vitamin D has hormonal functions, regulating body growth and development, cell differentiation, immunity, inflammatory reactions, etc. through vitamin D receptors. "In recent years, a large number of studies have found that the low level of vitamin D in the body is closely related to hypertension, cancer, diabetes, cardiovascular and cerebrovascular diseases, autoimmune diseases, and some infectious diseases such as tuberculosis and influenza," Rongshuang said. Vitamin D deficiency is quite common worldwide. Studies have shown that the global severe vitamin D deficiency rate is 15.7%, with a deficiency rate of 44.7%. The Scientific Research Report on Dietary Guidelines for Chinese Residents (2021) also pointed out that from 2016 to 2017, the serum vitamin D deficiency rate of children and adolescents aged 6-17 in China was 18.6%; In 2015, the vitamin D deficiency rate among adults aged 18 and above in China was 21.4%. For most people, vitamin D deficiency can affect bone calcification, causing mineral abnormalities in bones and teeth. In addition, a lack of vitamin D can also cause varying degrees of harm to people of different age groups. Lack of vitamin D in infants and young children is not only prone to rickets, but may also lead to softening and bending of bones due to abnormal calcification, such as the formation of "X" or "O" shaped legs, protruding sternum, delayed closure of fontanels, narrowing of pelvis, and spinal curvature. At the same time, a lack of vitamin D often leads to poor development of abdominal muscles in infants and young children, resulting in abdominal bulges; In terms of teeth, it can easily lead to delayed tooth emergence, sparse and concave cavities and permanent teeth. Pregnant women are prone to osteomalacia when lacking vitamin D, which mainly manifests as osteomalacia and easy deformation, and pelvic deformation can lead to difficult labor. Due to decreased liver and kidney function, poor gastrointestinal absorption, and reduced outdoor activities, the levels of vitamin D in the elderly are often lower than those in the young. Elderly people are prone to osteoporosis when lacking vitamin D, which increases their risk of fractures. Excessive supplementation of vitamin D is detrimental to health. So, how should we scientifically supplement vitamin D? Regular exposure to the sun is the best way to provide both affordable and effective vitamin D supplementation for the human body. Daily exposure to sunlight from 9-10 a.m. or 4-5 p.m