Vitamin D deficiency is a global health concern that is associated with various diseases. The influence of vitamin D on bone metabolism is so important that such a deficiency may cause fractures and a reduction in bone mineral density. Natural foods provide a limited intake of vitamin D. Vitamin D is a fat-soluble vitamin that is mainly produced in the skin after exposure to sunlight. UV-B rays convert 7-dehydrocholesterol, a precursor of cholesterol, to pre-vitamin D3, which then isomerizes to cholecalciferol (Vitamin D3.) Vitamin D3 transforms into calcidiol (25(OH)D), which subsequently transforms into the active form, calcitriol (1.25(OH)2D). 1.25(OH)2D maintains calcium and phosphorus homeostasis through vitamin D receptor (VDR). Recent studies have reported that vitamin D is involved in energy metabolism, inflammation, and the immune response. Furthermore, vitamin D deficiency has been reported to influence respiratory diseases, rheumatoid arthritis, cancer, diabetes, and pregnancy-related complications.