The common name for the disease caused by a deficiency of vitamin D is rickets in children and osteomalacia in adults. Rickets leads to weak and soft bones in children, often causing skeletal deformities such as bowed legs and growth retardation. In adults, osteomalacia results in bone pain and muscle weakness. Vitamin D is crucial for calcium absorption and bone health, and a deficiency can occur due to insufficient sunlight exposure, inadequate dietary intake, or malabsorption issues. Treatment typically involves vitamin D supplementation and dietary changes to improve bone strength and overall health.