Final answer:
Fortified food sources of vitamin D in the US include fish like salmon and tuna, milk, and breakfast cereals. Teenagers should intake 5 micrograms (200 IU) of vitamin D per day, which can also be produced by the body when exposed to sunlight. In the absence of sufficient sunlight or dietary sources, vitamin D supplements may be prescribed.
Step-by-step explanation:
The student is asking about fortified food sources of vitamin D available in the United States. Vitamin D can be obtained from fish and is added to other foods such as milk, soy milk, and breakfast cereals. It is important for teenagers to receive 5 micrograms (200 IU) of vitamin D daily. Specific examples include a 3½-ounce cooked portion of salmon which provides 360 IU of vitamin D, and an 8-ounce glass of fortified milk with about 100 IU of vitamin D. Sources such as cod liver oil, fish liver oil, egg yolks, and animal liver are rich in vitamin D. Sunlight exposure is also a critical way the body produces vitamin D, particularly through the action of ultraviolet light on 7-dehydrocholesterol in the skin. For individuals not receiving enough sunlight, vitamin D deficiency can be an issue, and a doctor may prescribe vitamin D supplements.