Final answer:
Among the provided choices about vitamin D, a marginal level may increase cancer risk, the skin produces it upon UV exposure, and milk is commonly fortified with it. Deficiency leads to rickets in children and osteomalacia in adults, which can contribute to osteoporosis.
Step-by-step explanation:
Among the statements about vitamin D, several are true:
- The deficiency disease associated with vitamin D in children is rickets, which leads to misshapen bones and bowleggedness. In adults, deficiency can lead to osteomalacia, not osteoporosis directly, but it can contribute to the development of osteoporosis by impairing bone density.
- A marginal level of vitamin D may increase the risk of various diseases, including cancer.
- Our bodies synthesize vitamin D through the skin's exposure to UV rays. The epidermal layer of human skin converts cholesterol to the inactive form of vitamin D3 when exposed to UV radiation.
- Milk is often fortified with vitamin D to help prevent deficiency in populations with limited exposure to sunlight.
Therefore, statements 2), 3), and 4) are correct. Statement 1) is not completely accurate as the deficiency disease directly associated with vitamin D is rickets in children and osteomalacia in adults; however, through its role in calcium homeostasis, vitamin D deficiency can be a contributing factor to the development of osteoporosis.