Vitamin D is the vitamin that comes from the sun. When exposed to sunlight, 7-dehydrocholesterol in the skin absorbs UV B radiation and is converted to previtamin D3, which in turn isomerizes into vitamin D3. Vitamin D3 is then hydroxylated in the liver and kidneys to become active vitamin D. Vitamin D is essential for bone and immune health. It helps the body absorb calcium and phosphorus, which are important for building and maintaining strong bones. Vitamin D also has other health benefits, such as improving mood, emotions, appetite, and digestion. However, it is important to balance sun exposure with other sources of vitamin D, such as food and supplements, to ensure adequate intake. People with inadequate sun exposure, including disabled people, infants, the elderly, dark-skinned people, and those who live at northern latitudes during the winter, are at risk of low vitamin D3 production, which can lead to a loss of bone density and an increased risk of fractures.