Vitamin D supplements don’t work consistently across different populations. Very few (~10%) of people can absorb dietary vitamin D. If you aren’t some form of Northern European, you probably need to take at least 10 times the daily recommended dose of vitamin D to influence your levels significantly.
Most people need sun!
Don't most people who take supplements just take 10X the RDA? It is still a tiny amount of supplement that is safer and costs a fraction of the indoor tanning or traveling often to somewhere with adequate Sun.
I’ve never talked to someone supplementing vitamin D who was aware at all.
I think that the correct approach would be start at 10x vitamin D with baseline bloodwork and adjust dosage from there.
But yeah I’m in the camp of “sun is good for you, in most cases.” I would be very unsurprised to find that there are precursor hormones released beyond vitamin D that impact efficacy. We don’t really understand the endocrine system very well.
I think that because we can see and understand the dermatological effects we overly weight them. Anecdotally older people I know who have not avoided the sun seem much better off mentally and physically, but I think because there isn’t a measurable reason we’re aware of, we completely discount any benefit.