positive regulation of vitamin D biosynthetic process

Definition

Target type: biologicalprocess

Any process that increases the rate, frequency or extent of a vitamin D biosynthetic process. Vitamin D biosynthesis is the chemical reactions and pathways resulting in the formation of vitamin D, any of a group of related, fat-soluble compounds that are derived from delta-5,7 steroids and play a central role in calcium metabolism. Specific forms of vitamin D include calciferol (ergocalciferol; vitamin D2) and cholecalciferol (calciol; vitamin D3). [CHEBI:27300, GOC:BHF, GOC:mah, ISBN:0471331309]

Positive regulation of vitamin D biosynthesis involves a complex interplay of factors, primarily centered around the conversion of 7-dehydrocholesterol (7-DHC) to cholecalciferol (vitamin D3) in the skin upon exposure to UVB radiation. This process is tightly regulated to ensure optimal vitamin D production while preventing excessive accumulation.

**Key Steps and Regulators:**

1. **UVB Radiation:** UVB radiation from sunlight triggers the conversion of 7-DHC to previtamin D3 in the skin. This is the initial and crucial step in vitamin D biosynthesis.

2. **Isomerization:** Previtamin D3 undergoes a thermal isomerization process, converting to vitamin D3 (cholecalciferol) over a few hours.

3. **Transport:** Vitamin D3 is then transported to the liver via binding proteins.

4. **Hydroxylation:** In the liver, vitamin D3 undergoes the first hydroxylation reaction, catalyzed by the enzyme 25-hydroxylase (CYP2R1), producing calcidiol (25-hydroxyvitamin D).

5. **Regulation in the Liver:** The level of calcidiol in the blood is tightly regulated by various factors, including dietary intake of vitamin D, UVB exposure, and circulating levels of parathyroid hormone (PTH).

6. **Further Hydroxylation:** Calcidiol is further hydroxylated in the kidneys by 1α-hydroxylase (CYP27B1), producing the biologically active form of vitamin D, calcitriol (1,25-dihydroxyvitamin D).

7. **Regulation in the Kidneys:** 1α-hydroxylase activity is influenced by circulating levels of calcium, PTH, and calcitriol itself. This negative feedback loop ensures that calcitriol levels are maintained within a specific range.

**Factors Influencing Positive Regulation:**

* **UVB Exposure:** Sufficient UVB radiation is essential for initiating the conversion of 7-DHC to vitamin D3.
* **Dietary Vitamin D Intake:** Consuming vitamin D-rich foods, such as fatty fish, eggs, and fortified milk, can supplement UVB exposure.
* **Parathyroid Hormone (PTH):** PTH stimulates 1α-hydroxylase activity in the kidneys, increasing calcitriol production.
* **Calcium Levels:** Low calcium levels stimulate PTH release, indirectly promoting calcitriol production.
* **Other Hormones:** Hormones like estrogen and growth hormone may also influence vitamin D synthesis and metabolism.

**Factors Influencing Negative Regulation:**

* **Vitamin D Deficiency:** Low vitamin D levels trigger a cascade of events aimed at increasing calcitriol production, including increased PTH secretion.
* **Excess Vitamin D:** High levels of vitamin D can inhibit further production, primarily by suppressing the activity of 1α-hydroxylase.

**Overall, positive regulation of vitamin D biosynthesis involves a coordinated effort of various factors, including UVB radiation, dietary intake, hormonal signals, and feedback mechanisms. This complex process ensures that adequate levels of active vitamin D are maintained for maintaining calcium homeostasis and supporting overall health.**'
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Proteins (1)

Compounds (18)