Vitamin D deficiency occurs due to a lack of sunlight exposure, poor diet, or certain medical conditions like kidney disease. It can lead to weak bones, muscle pain, fatigue, and even mood changes such as depression. To combat this deficiency, spending 10–30 minutes in sunlight daily can help the body naturally produce vitamin D. Consuming vitamin D-rich foods like fatty fish (salmon, mackerel), egg yolks, and fortified dairy products is also beneficial. In cases where dietary intake and sunlight exposure are insufficient, taking vitamin D supplements may be necessary, especially during winter months or for those with higher risk factors.