[Jeriko]

If you are trying to use it to treat mild depression specifically, a placebo effect is great! Placebo effects get a bad rap. If something improves your subjective quality of life that should be considered a win, especially for depression.

Honestly the best thing vitamin D has going for it is being super inexpensive and safe. Because of that you can supplement vitamin D for almost any reason and expect to see at worst a very small cost (someone up thread said 3 cents a day, which seems in the ball park) and at best a significant subjective benefit (even if it's from a placebo effect).

[James_Henry]

Placebo effects can be great; they can mask underlying issues though. Also, if you actually have a vitamin D deficiency (or some other health issue), it could be good to know why. Perhaps your kidneys are having issues, for instance.