25-hydroxyvitamin D

Definition

25-hydroxyvitamin D, also known as calcifediol, is the main circulating form of vitamin D in the body. It is produced in the liver when vitamin D from the diet or skin exposure to sunlight is converted into 25-hydroxyvitamin D, which is then further metabolized in the kidneys to the active form, 1,25-dihydroxyvitamin D. This metabolite plays a crucial role in regulating calcium and phosphate homeostasis, bone health, and various other physiological processes.

5 Must Know Facts For Your Next Test

1. 25-hydroxyvitamin D is the primary circulating form of vitamin D in the body and is used to assess an individual's vitamin D status.
2. The conversion of vitamin D to 25-hydroxyvitamin D occurs in the liver, and this metabolite is then further converted to the active form, 1,25-dihydroxyvitamin D, in the kidneys.
3. Adequate levels of 25-hydroxyvitamin D are necessary for the proper absorption and utilization of calcium and phosphate, which are essential for maintaining bone health.
4. Bisphosphonates, a class of drugs used to treat osteoporosis, can increase the production of 25-hydroxyvitamin D, thereby enhancing the bioavailability of vitamin D.
5. Estrogen receptor modulators, such as raloxifene, may also influence the metabolism and actions of 25-hydroxyvitamin D, affecting bone health and other physiological processes.

Review Questions

• Explain the role of 25-hydroxyvitamin D in the regulation of calcium and phosphate homeostasis.
  • 25-hydroxyvitamin D is the main circulating form of vitamin D in the body. It is converted in the kidneys to the active form, 1,25-dihydroxyvitamin D, which plays a crucial role in regulating calcium and phosphate levels. 1,25-dihydroxyvitamin D enhances the intestinal absorption of calcium and phosphate, promotes the mobilization of calcium from bone, and helps maintain optimal serum calcium and phosphate concentrations. This is essential for maintaining bone health and supporting various physiological processes that depend on proper mineral homeostasis.
• Describe how bisphosphonates, a class of drugs used to treat osteoporosis, may influence the metabolism of 25-hydroxyvitamin D.
  • Bisphosphonates, a class of drugs commonly used to treat osteoporosis, can indirectly affect the metabolism of 25-hydroxyvitamin D. These drugs work by inhibiting osteoclast-mediated bone resorption, which can lead to an increase in the production of parathyroid hormone (PTH). PTH, in turn, stimulates the conversion of 25-hydroxyvitamin D to the active form, 1,25-dihydroxyvitamin D, in the kidneys. This increased production of the active vitamin D metabolite can enhance the bioavailability of vitamin D, which is important for maintaining bone health and calcium-phosphate homeostasis in patients with osteoporosis.
• Analyze the potential impact of estrogen receptor modulators on the metabolism and actions of 25-hydroxyvitamin D, and discuss the implications for bone health and other physiological processes.
  • Estrogen receptor modulators, such as raloxifene, are a class of drugs that can influence the metabolism and actions of 25-hydroxyvitamin D. Estrogen plays a role in regulating vitamin D metabolism, and changes in estrogen levels can affect the conversion of 25-hydroxyvitamin D to the active form, 1,25-dihydroxyvitamin D. Estrogen receptor modulators, by selectively modulating estrogen's effects in different tissues, may alter the production and actions of 1,25-dihydroxyvitamin D. This can have implications for bone health, as vitamin D is essential for calcium and phosphate homeostasis, and for supporting the mineralization and maintenance of bone. Additionally, the effects of estrogen receptor modulators on 25-hydroxyvitamin D metabolism may extend to other physiological processes that are influenced by vitamin D, such as immune function, cardiovascular health, and cancer prevention.

Related terms

Vitamin D:

Vitamin D is a fat-soluble vitamin that can be obtained from the diet or produced in the skin through exposure to ultraviolet B (UVB) radiation from sunlight. It is essential for maintaining calcium and phosphate homeostasis, supporting bone health, and regulating various other bodily functions.

1,25-dihydroxyvitamin D: 1,25-dihydroxyvitamin D, also known as calcitriol, is the active form of vitamin D. It is produced in the kidneys from 25-hydroxyvitamin D and plays a crucial role in regulating calcium and phosphate levels, promoting bone mineralization, and modulating various physiological processes.

Parathyroid Hormone (PTH): Parathyroid hormone is a hormone secreted by the parathyroid glands that helps maintain calcium and phosphate homeostasis. It stimulates the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, which in turn increases calcium absorption and mobilization from bone.