Which vitamin is primarily produced when the skin is exposed to sunlight?

The production of vitamin D in the body is primarily triggered by skin exposure to sunlight, specifically ultraviolet B (UVB) rays. When the skin absorbs these rays, a chemical reaction occurs that converts a cholesterol derivative in the skin into vitamin D3, which is then transformed into the active form of vitamin D through a series of processes in the liver and kidneys. This vitamin is crucial for maintaining bone health, as it helps the body absorb calcium and phosphorus.

In contrast, vitamin A is primarily obtained from dietary sources such as carrots and liver, and is not produced in the skin. Vitamin C, also sourced from various fruits and vegetables, plays a vital role in immune function and skin health, but is not synthesized by the skin through sunlight exposure. Vitamin E is another important nutrient found in foods and is known for its antioxidant properties, but like vitamins A and C, it is not produced in the body through sunlight exposure. Thus, vitamin D is uniquely associated with sun exposure, making it the correct answer.