Vitamin D is a fat-soluble vitamin that plays a crucial role in maintaining bone health, calcium homeostasis, and various other physiological processes in the body. It is often referred to as the 'sunshine vitamin' because the human body can synthesize it when the skin is exposed to ultraviolet B (UVB) radiation from sunlight. Vitamin D is closely linked to the topics of bone formation and development, exercise, nutrition, and calcium homeostasis. It also has important interactions with the parathyroid glands, organs with secondary endocrine functions, chemical digestion and absorption, and overall nutrition and diet.