Vitamin D and calcium are the “double shot” in the treatment of osteoporosis and always need to be taken at the same time to achieve the best results. What are the instructions for its use? Author: Xu Naijia, Attending Physician, Department of Endocrinology, Wuhan Hospital of Traditional Chinese Medicine Source: Medical Community Endocrine Channel Vitamin D from skin synthesis or food sources is first hydroxylated in the liver by 25-hydroxylase to 25(OH)D, and then further hydroxylated in the kidney and peripheral tissues by 1-hydroxylase to 1,25(OH)2D, the active vitamin D, which binds to the vitamin D receptor and performs physiological functions. Maintaining proper vitamin D levels is beneficial for bone health, maintaining muscle strength, improving physical stability, and reducing the risk of fracture. Therefore, in the field of osteoporosis treatment, vitamin D has been used as a basic preventive and therapeutic agent together with calcium. Do you understand these three things to know when using vitamin D? Knowing vitamin D levels before use 25(OH)D is bound to vitamin D binding protein in serum, the most abundant and stable form of vitamin D circulating in the body, and is therefore used to evaluate the body’s vitamin D levels. Our Guidelines for the Application of Vitamin D and Adult Bone Health (2014 Edition) state that serum 25(OH)D <30 nmol/L (2.5 nmol/L = 1 ng/mL) is vitamin D deficiency; ② serum 25(OH)D of 30-49.9 nmol/L is vitamin D insufficiency; ③ serum 25(OH)D ≥50 nmol/L is Vitamin D is sufficient. Patients who need to start treatment with anti-osteoporosis drugs (e.g. bisphosphonates, calcitonin, etc.) should preferably have their blood 25(OH)D adjusted to 75 nmol/L before using the drugs. Must know 2: Choose the right vitamin D preparation The beneficial effects of vitamin D on the human body are directly related to 25(OH)D levels, and its anti-cancer and immune modulating effects on bones require adequate 25(OH) D levels as raw material support. Currently available vitamin D preparations are regular vitamin D (D2 and D3) and vitamin D analogs [1-alpha-OH-D3 and 1,25(OH)2D3]. Vitamin D is hydroxylated to 25(OH)D by 25-hydroxylase in the liver, so the best way to increase serum 25(OH)D levels is to supplement with regular vitamin D. Vitamin D2 or D3 undergoes 2 hydroxylations to become active 1,25(OH)2D and is therefore suitable for patients with normal hydroxylation in the liver and kidneys. In addition, most studies now believe that supplementation with vitamin D2 requires higher doses to be equivalent to vitamin D3, so vitamin D3 is preferred. Among the vitamin D analogues, 1-alpha-OH-D3 can be converted to active vitamin D only after 25-hydroxylation in the liver, i.e., 1,25(OH)2D, 1,25(OH)2D3 works directly, and both are suitable for patients with renal insufficiency and impaired 1-hydroxylation function, while the application of 1-alpha-OH-D3 presupposes normal liver function. When the serum 25(OH)D concentration decreases, the body can still keep 1,25(OH)2D at normal or even slightly high levels by increasing the synthesis and activity of 1-hydroxylase through the kidneys, so it is generally not prone to 1,25(OH)2D deficiency. In addition, because of the extremely high affinity of 1,25(OH)2D for the receptor, there is a risk of hypercalcemia and hypercalcemia after exogenous oversupplementation. In terms of reducing non-vertebral fractures and falls, the available systematic evaluations show a slight advantage of vitamin D analogs over regular vitamin D, but their effectiveness needs to be further confirmed due to the lack of head-to-head randomized controlled trials. In contrast, 1,25(OH)2D3 increases the risk of hypercalcemia significantly more than regular vitamin D. Therefore, vitamin D analogs may be used in patients of advanced age, at high risk of falls, or with hepatic or renal insufficiency to rapidly improve symptoms and muscle function. In the long run, if the liver and kidneys have normal hydroxylation, it is still necessary to supplement with regular vitamin D to bring 25(OH)D up to standard in order to perform its anti-cancer, immune modulating, and metabolic improving functions. The 2011 edition of China's "Guidelines for the Prevention and Treatment of Primary Osteoporosis" recommends a daily supplemental dose of vitamin D of 800 to 1200 U/d for the treatment of primary osteoporosis. Because vitamin D is fat-soluble and requires fat to aid in absorption, it is recommended that it be taken with meals. In areas where oral preparations are not available for sale, vitamin D3 injections (300,000 U/d) can be chosen as an intramuscular injection every 3 months provided that the patient has normal liver and kidney function. Ideally, blood 25(OH)D should be adjusted to 75 nmol/L as previously described, especially when treated with anti-osteoporosis therapy. For patients with vitamin D deficiency, 50,000 U of vitamin D3 can be supplemented weekly for 4 to 6 weeks, and then anti-osteoporosis therapy can be initiated. Small doses of vitamin D analogues can also be applied, with the usual doses of 0.25-0.50 μg/d for 1,25(OH)2D3 and 0. 25-1. 00 μg/d for 1-alpha-OH-D3. Patients using vitamin D should monitor blood and urine calcium and adjust the dose promptly. Since the half-life of 25( OH) D is 15-20 d, for should be monitored every 3 months and should be maintained until 75 nmol/L is reached, and the maintenance dose after reaching the standard can be individualized.