[Tanya Marie Squirrel]

recent studies (perhaps not so recent) indicate depression and suicidal tendencies are possibly linked with vitamin D deficiency, you can safely take up to 5000 I.u. (international units , that's how its sold) per day. it will take up to a month for you to see change. I, myself, take a 5000 i.u. gelcap per day. it has done wonders for my depression.

whether it is a placebo effect or factual, it is still out for speculation.
http://www.webmd.com/depression/news/20120627/vitamin-d-deficiency-linked-to-depression