Deficiency diseases occur when the body lacks essential nutrients, such as vitamins and minerals, critical for its healthy functioning. For instance, a lack of vitamin C can lead to scurvy, characterized by symptoms like bleeding gums and bruising, while vitamin D deficiency can cause rickets in children, resulting in bone deformities. Iron deficiency leads to anemia, marked by fatigue and weakness. These diseases highlight the importance of a balanced diet enriched with necessary nutrients. Prevention and treatment involve dietary adjustments or supplementation to replenish missing nutrients, thereby restoring health and preventing long-term complications.