Moving from Canada to California did a lot to help my depression. It's hard to not feel good on a beautiful sunny day

If your depression is caused by lack of vitamin D it stands to reason that vitamin D helps fighting it. But not every depression is caused by vitamin D deficiency, so it doesn't always do wonders

That may be true but studies have shown that most people in the US are deficient. Our indoor lifestyle is to blame, and vit D is not readily available in food as other nutrients are. It is either sun or supplements.

Interesting site. I generally read what Examine.com (https://examine.com/supplements/vitamin-d/) has to say about a supplement.

The graphs you link to show Vitamin D having "good" evidence of improving well-being, well above the "worth it" line.

But I would expect studies showing Vitamin D only effective in some cases of depression, just like Coffee is helpful in some cases of headaches. Depression seems much closer to being a symptom than to being a disease. So anything that fights a root cause of depression will only work for those people whose depression is caused by that specific root cause, and will have many people reporting it doesn't work for them at all.

I would guess that most human health issues that are universal across the species have been discovered at this point. Vitamin C and Iodine deficiencies cause serious problems for all humans. Large studies that see some small effect are likely to be variance where a few people are have large positive effects and others not or even negative. That is your individual genetics and other factors are going to determine if some advice is useful for you. Listening to your parents and grandparents is probably more useful than reading almost all modern health studies.