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Vitamin D Metabolism and 25 Hydroxyvitamin D

What is vitamin D?

Vitamin D refers to a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc. There are approximately 30 molecules in the Vitamin D group, but the two most significant forms are vitamin D2 and vitamin D3, vitamin D2 also named ergocalciferol, which is synthesized by plants and is not produced by the human body, it has a purely dietary source, predominantly from yeasts, vitamin D3 also named cholecalciferol, which is made in large quantities in the skin when sunlight strikes bare skin, It can also be ingested from diet like oily fish, egg yolks, and fortified foods.

Resurrection of vitamin D deficiency and rickets. Vitamin D, in either the D2 or D3 form, is considered biologically inactive until it undergoes two enzymatic hydroxylation reactions.

Vitamin D metabolism

During exposure to sunlight, 7-dehydrocholesterol in the skin absorbs solar UVB radiation and is converted into Pre-Vitamin D3 (pre-D3). DHCR7 encodes the enzyme 7-dehydrocholesterol reductase, which converts 7-dehydrocholesterol to cholesterol, thereby removing a precursor of 25-hydroxyvitamin D3 from the synthetic pathway of vitamin D3. Heat causes isomerization of pre-vitamin to vitamin D in the skin. Then vitamin D bound to plasma transport protein (D binding protein, also known as Gc protein) transport through blood to liver, and is hydroxylated in the liver at position 25 to form 25-hydroxyvitamin D (calcidiol) by the microsomal enzyme vitamin D 25-hydroxylase, which is encoded by the CYP2R1 and CYP27A1 genes in the liver. The 25 hydroxyvitamin D is the precursor of 1,25 hydroxyvitamin D 3 (calcitriol), which is a major form of vitamin D to be stored in human body, it circulates bound to a specific plasma carrier protein, vitamin D binding protein, and the half-life approximately 15 days at a concentration of 25-200 nmol/L.

The following reaction takes place in the kidney, mediated by 1α-hydroxylase, which converts 25 hydroxyvitamin D to the biologically active hormone, 1,25-dihydroxyvitamin D (calcitriol), and is encoded by CYP27B1 gene, which is also expressed in several extra-renal tissues, but its contribution to calcitriol formation in these tissues is unknown. The renal synthesis of calcitriol is tightly regulated by two counter-acting hormones, with up-regulation via parathyroid hormone (PTH) and down-regulation via fibroblast-like growth factor-23 (FGF23). The rate-limiting step in catabolism is the degradation of 25 hydroxyvitamin D and 1,25-dihydroxyvitamin D (calcitriol) to 24,25 hydroxyvitamin D and 1,24,25 hydroxyvitamin D, respectively, which occurs through 24-hydroxylation by 25-hydroxyvitamin D 24-hydroxylase (24-OHase), encoded by the CYP24A1 gene. 24,25 hydroxyvitamin D and 1,24,25 hydroxyvitamin D are consequently excreted. Following its synthesis in the kidney, calcitriol binds to DBP to be transported to target organs. The biological actions of calcitriol, involve regulation of gene expression at the transcriptional level, and are mediated through binding to a vitamin D receptor (VDR), located primarily in the nuclei of target cells. VDR is a transcription factor that partners with other transcription factors such as retinoid X receptor (RXRA or RXRB) . The main established actions of 1,25 hydroxyvitamin D collectively increase calcium in the body and modulate the skeleton. It increases the intestinal absorption of calcium and phosphate, decreases renal excretion of calcium and phosphate, suppresses PTH production, and regulates osteoblast function and bone resorption. It has been suggested that 1,25 hydroxyvitamin D has roles beyond the calcium-skeletal axis.


ELISA Kit

25OHD
Cat. No. Product Size Sensitivity
DEIA4458 25-OH-Vitamin-D ELISA Kit 96 T 1.8 ng/mL
DEIA-BJ648 Human 25 Hydroxy Vitamin D3 ELISA kit 96 T 0.1 nmol/L
DEIA-BJ2145 Rat 25 Hydroxy Vitamin D3 ELISA Kit 96 T 0.1 ng/mL
1,25(OH)2D
Cat. No. Product Size Sensitivity
DEIA-BJ574 Human 1,25-dihydroxyvitamin D3 ELISA kit 96 T 0.1 nmol/L
DEIA001J 1,25-(OH)2 Vitamin D ELISA Kit 96 T 4.8 pg/mL

Antibody

25OHD
Cat. No. Product Conjugate Host Application
DMAB4488S Anti-25-OH Vitamin D monoclonal antibody Unconjugated Sheep ELISA
DMAB2914 Anti-Calcifediol monoclonal antibody, clone C2531M Unconjugated Mouse ELISA
1,25(OH)2D
Cat. No. Product Conjugate Host Application
DMAB2913 Anti-1,25 (OH)2 Vitamin D3 monoclonal antibody, clone B1254M Unconjugated Mouse ELISA
DMAB9770 Anti-1,25 (OH)2 Vitamin D3 monoclonal antibody, clone JE2,26B Unconjugated Mouse ELISA
DMABA-09252 Anti-1, 25 (OH)2 VITAMIN D3 Monoclonal Antibody, clone C2364N Unconjugated Mouse ELISA

Antigen

Cat. No. Product Type Conjugate Application
DAG03219 25-OH Vitamin D3-BSA Conjugated Synthetic BSA ELISA

Vitamin D Level

25-hydroxyvitamin D (25(OH)D) is the major circulating form of vitamin D and has a fairly long circulating half-life of 15 days; thus, the total serum 25(OH)D level is currently considered the best indicator of vitamin D supply to the body from cutaneous synthesis and nu tritional intake. In medicine, a 25hydroxyvitamin D blood test is used to determine how much vitamin D is in the body. The blood concentration of 25 hydroxyvitamin D is considered the best indicator of vitamin D status.

<20ng/ml 30-60ng/ml 20-100ng/ml >150ng/ml
Deficiency Preferred range Reference range Intoxication

Vitamin D and Health

The lack of vitamin D will directly affect the balance of human metabolism and be harmful to human health. Getting the proper amount of vitamin D may help prevent several serious health conditions. According to current investigation, the lack of vitamin D can be found in 10 billion or more all over the world, especially in the young, the older and the pregnant. The lack of vitamin D can cause rickets in children and osteoporosis in older people. In recent years, a large number of papers reported that the lack of vitamin D closely linked with many diseases.

Osteoporosis
Vitamin D helps your body absorb and use calcium, which you need for strong bones. Osteoporosis is most often associated with inadequate calcium intakes, but insufficient vitamin D contributes to osteoporosis by reducing calcium absorption.

Cancer
Laboratory and animal evidence that getting enough vitamin D may lower your risk of certain cancers, especially of the colon, breast, prostate, skin, and pancreas. Strong biological and mechanistic bases indicate that vitamin D plays a role in the prevention of colon, prostate, and breast cancers.

Heart Disease
Population studies suggest that people with low levels of vitamin D have a greater risk of developing heart disease, including heart attack, stroke, and heart failure compared to people with higher levels of vitamin D. Low levels of vitamin D may increase the risk of calcium build up in the arteries.

So it becomes more and more important for predicting the risk of relative diseases and the statue of nutrition to detect the content of vitamin D in the body.

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