Used primarily to prevent and treat vitamin D deficiency, which can lead to weakened bones and conditions such as rickets in children and osteomalacia in adults. It supports calcium absorption in the gut, helping maintain strong bones and teeth. Commonly added to fortified foods like milk, cereals, and plant-based beverages. Widely available in dietary supplements for immune support and overall health. Also used in medical treatments for chronic kidney disease and certain hormonal disorders affecting calcium balance. Used in animal feed to ensure proper growth and bone development in livestock and pets.