Final answer:
Sunlight is responsible for producing 80-90% of the body's vitamin D. This vitamin is essential for the absorption of calcium and maintaining bone health, with supplements available in case of deficiency.
Step-by-step explanation:
Sunlight provides 80-90% of the body's vitamin D. Vitamin D3, cholecalciferol, is synthesized in the skin when cholesterol in the epidermis is exposed to ultraviolet (UV) radiation. This occurs through the action of sunlight on the skin, which photochemically produces vitamin D3 from 7-dehydrocholesterol. Even though certain foods like fatty fish, fortified milk, and cereal are dietary sources of vitamin D, the majority of an individual's necessary vitamin D is obtained from sun exposure. If sunlight exposure is inadequate, a deficiency can occur, leading to bone conditions like rickets in children and osteomalacia in adults. In such cases, vitamin D supplements may be prescribed by a healthcare professional.