The main biological roles of vitamin D beyond bone health

Vitamin D has several important biological roles beyond bone health:

Immune System Regulation: Vitamin D acts as a potent modulator of the immune system. Many immune cells, including macrophages, dendritic cells, and T lymphocytes, have vitamin D receptors (VDRs) and can activate vitamin D locally to regulate immune responses. Vitamin D enhances the pathogen-fighting effects of these cells, helping to reduce infections and modulate inflammation, which may protect against autoimmune diseases.clevelandclinic+1
Cardiovascular Health: Vitamin D receptors are found in heart muscle cells, vascular smooth muscle, and endothelial cells. Vitamin D influences cardiovascular function by regulating blood pressure and heart muscle growth. Deficiency has been associated with hypertension, cardiac hypertrophy, and increased risk of cardiovascular events.pmc.ncbi.nlm.nih
Muscle Function: Vitamin D contributes to muscle strength and function. VDR expression in muscle decreases with age, and low vitamin D levels correlate with muscle weakness, sarcopenia (loss of muscle mass), and higher risk of falls in older adults.pmc.ncbi.nlm.nih
Cell Growth and Differentiation: Vitamin D regulates the expression of hundreds of genes involved in cellular differentiation and growth, which is important for maintaining normal cell cycles and may have implications in cancer prevention.med.libretexts+1
Neurological Function: Vitamin D receptors are also present in the brain. Low vitamin D is linked to cognitive decline, increased risk of Alzheimer's disease, depression, and other neurological disorders. It may regulate neuronal calcium homeostasis and neurotransmitter function.pmc.ncbi.nlm.nih
Metabolic and Endocrine Functions: Vitamin D influences insulin secretion and sensitivity, potentially affecting diabetes risk. It also impacts inflammation pathways and other hormonal regulations related to obesity and aging.med.libretexts+1

In sum, vitamin D is a key hormone-like vitamin with widespread influence on immunity, cardiovascular health, muscle function, brain health, and cellular regulation beyond its classical role in bone metabolism.