Vitamin D: Nutrient, Hormone, and Immunomodulator.

Area of Science:

• Immunology
• Endocrinology
• Nutritional Science

Background:

• Classical vitamin D functions involve calcium-phosphorus homeostasis and bone metabolism.
• Vitamin D deficiency is linked to chronic inflammatory and immune-deregulated conditions like diabetes, asthma, and rheumatoid arthritis.
• Emerging evidence suggests a significant role for vitamin D in modulating immune responses.

Purpose of the Study:

• To review experimental data and clinical observations on the immunomodulatory properties of vitamin D.
• To explore the hypothesis of disease-specific alterations in vitamin D metabolism.
• To reinforce the understanding of vitamin D's role in maintaining a healthy immune system.

Main Methods:

• Review of existing experimental studies and clinical observations.
• Examination of vitamin D receptor (VDR) expression in immune cells.
• Analysis of local vitamin D metabolism within immune cells.

Main Results:

• Vitamin D receptor (VDR) is expressed on most immune cells, including lymphocytes, monocytes, macrophages, and dendritic cells.
• Immune cells can locally metabolize vitamin D to its active form, 1,25(OH)₂D₃.
• Vitamin D and VDR signaling exhibit anti-inflammatory effects and suppress autoimmunity.

Conclusions:

• Vitamin D significantly modulates immune function through non-classical actions.
• Vitamin D promotes regulatory T-cell differentiation and dendritic cell maturation.
• Vitamin D suppresses pro-inflammatory responses, including Th17 cell activity and cytokine secretion.