The reference range for vitamin D is 75-375 nmol/L, for vitamin D₂ is 75-150 nmoll/L, and for vitamin D₃ is 25-65 ng/ml. If it is lower than the reference range, it can be considered that there is a deficiency of vitamin D in the organism. Vitamin D (abbreviated as VD) is a nutrient necessary for maintaining the life of higher animals, the most important of which are vitamin D₃ (cholecalciferol, cholecalciferol), and vitamin D₂ (osseocalciferol). The main causes are dietary vitamin D deficiency and insufficient sunlight exposure, the latter being particularly important. Vitamin D deficiency in the human body can lead to the development of a variety of diseases, such as osteochondrosis, osteoporosis, cardiovascular diseases, and autoimmune diseases. If the test results show that the patient is already deficient in vitamin D, it is necessary to seek medical treatment in a timely manner, which can be supplemented through daily sun exposure and outdoor activities, or oral vitamin D under the guidance of a doctor, to avoid physical discomfort caused by vitamin D deficiency.