Final answer:
Vitamin D deficiency can be caused by insufficient sunlight, use of sunscreen and protective clothing, and kidney disease, while ample sunlight and lighter skin pigmentation usually promote its synthesis.
Step-by-step explanation:
Vitamin D synthesis is a multi-step process, which begins in the skin when exposed to UV radiation and ends with the active form of vitamin D, crucial for bone health and calcium absorption. Conditions that can lead to a deficiency include limited sunlight exposure, wearing protective clothing and sunscreen outdoors, and having kidney disease, which impairs the conversion of vitamins to their active form. Whereas, living in a region with a lot of sunlight and having a lighter skin pigmentation typically contribute to better vitamin D synthesis.