Solar radiation is essential for life. The sun provides thermal energy for photosynthesis in plants and causes cutaneous synthesis of vitamin D in vertebrates, including humans. Depending on skin color, the proper dose of UVB radiation releases approximately 20,000 IU vitamin D3 into the circulation within 24 hours. For optimal functioning, vitamin D should be available on a daily basis to ensure stable circulating concentrations because of its short circulating halflife. The newly recognized biological roles of vitamin D are complex: VDR polymorphisms modulate the risk of some cancers, balanced vitamin D intake is required for cardiovascular health, and the vitamin has a role in glucose-induced insulin secretion and modulation of the inflammatory response. Because of its highly integrated relationships with health, vitamin D sufficiency is essential in all stages of life but especially for breastfed Infants, children with poor diets, and older adults. Key words: Vitamin D, intake, Vitamin D roles, vulnerable groups requirements.