Vitamin D deficiency occurs when the body does not get enough vitamin D, which is essential for maintaining healthy bones and supporting the immune system. This vitamin helps the body absorb calcium, a crucial mineral for bone health. Deficiency can result from limited sun exposure, poor dietary intake, or certain medical conditions that affect absorption. Symptoms of vitamin D deficiency may include fatigue, bone pain, and muscle weakness. In severe cases, it can lead to conditions like osteoporosis in adults or rickets in children. Regular sun exposure, a balanced diet, and supplements can help prevent deficiency.