AI Overview Vitamin D is a fat-soluble vitamin essential for overall health, particularly for bone health, calcium absorption, and immune function. It's also involved in muscle function and brain health. People can obtain vitamin D through sun exposure, dietary sources, and supplements.  Here's a more detailed look: Importance for Bone Health: Vitamin D helps the body absorb calcium, a key building block for strong bones and teeth. It plays a crucial role in preventing osteoporosis, a condition that weakens bones.  Immune System: Vitamin D is essential for a healthy immune system, helping the body fight off infections.  Muscle Function: Vitamin D is necessary for normal muscle function.  Brain Health: Vitamin D may play a role in brain function and cognitive health.  Other Potential Benefits: Some research suggests vitamin D may have a role in reducing inflammation, improving cardiovascular health, and preventing certain chronic diseases, although more research is needed.  Sources of Vitamin D: Sunlight: The body produces vitamin D naturally when exposed to sunlight, particularly UVB rays.  Food: Fatty fish (salmon, tuna, mackerel), fortified milk, and eggs are good sources of vitamin D.  Supplements: Vitamin D supplements are commonly used to prevent and treat vitamin D deficiency.  Vitamin D Deficiency: Causes: Lack of sun exposure, poor diet, and certain medical conditions can lead to vitamin D deficiency.  Symptoms: Symptoms can include fatigue, bone pain, and increased risk of infections.  Risk Groups: People with dark skin, those who live in northern latitudes, and individuals with certain medical conditions are at higher risk of vitamin D deficiency.