Final answer:
Cancers and diabetes mellitus have been linked to lower levels of vitamin D in the body, which plays a critical role in immunity and bone health.
Step-by-step explanation:
Some cancers and diabetes mellitus have been linked to lower levels of vitamin D in the body. Vitamin D is not only crucial for bone health but also plays a vital role in the body's general immunity against bacterial, viral, and fungal infections. Recent studies have suggested that lower levels of vitamin D may be associated with an increased risk of certain cancers. On the other hand, while not directly linked to diabetes, vitamin D insufficiency can potentially affect the body's glucose metabolism, which is relevant to the development of diabetes mellitus.