> My understanding is that (a) utilization of dietary vitamin D is significantly lower than naturally produced D (from sun exposure)...

The end product of UVB irradiated skin (i.e., sunlight) is vitamin D3. (D3 is "activated" locally in tissues utilizing it.) Ingested D3 supplements effectively add to the body's supply, though the optimum intake is controversial and varies among individuals.

One difference between sunlight and supplements is that D3 production via UVB exposure has an upper bound, only so much can be made because there's a limited amount of substrate available in skin cells to convert to vitamin D. The upshot is sunlight is "safer" re: potential toxicity of excessive vitamin D intake.

AFAIK vitamin D is unique among nutritional factors in its reliance on UVB exposure. Don't know of any other micronutrients directly related to sunlight, but possible there's something I've overlooked.