Why Vita d is called as hormone?

Vitamin D is often referred to as a hormone because it is produced in the body in response to sunlight exposure and plays a crucial role in regulating various physiological processes. Unlike traditional vitamins, which must be obtained from diet, vitamin D can be synthesized by the skin when exposed to ultraviolet B (UVB) rays. Once formed, it undergoes further conversion in the liver and kidneys to become its active form, which acts on various tissues to regulate calcium and phosphate metabolism, immune function, and other critical biological functions. This hormone-like action distinguishes it from other vitamins and underscores its significant role in maintaining overall health.