[pmahoney]

This paper, "Insufficient Sun Exposure Has Become a Real Public Health Problem" [1] states "thus, serum 25(OH)D as an indicator of vitamin D status may be a proxy for and not a mediator of beneficial effects of sun exposure".

That is, while vitamin D can be used to deduce someone's amount of sun exposure, the benefits of sun exposure are not coming from the vitamin D.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400257/