The vitamin primarily produced in the skin upon exposure to sunlight is vitamin D. When UV rays penetrate the skin, a chemical reaction occurs that converts a form of cholesterol into vitamin D. This nutrient is essential for calcium absorption, thereby supporting bone health and playing a crucial role in the immune system. Vitamin D deficiency can lead to various health issues, including weakened bones, increased risk of chronic diseases, and impaired immune function. Hence, adequate sun exposure and/or supplementation can help maintain optimal vitamin D levels for overall health.