For another perspective, I get a yearly physical and about 15 years ago I was having elevated ALT/AST liver enzyme results in my blood test. This lasted two years in a row while my primary care physician ran a dozen tests including for hepatitis trying to figure out what was causing it. Everything came back negative. She asked me if I took a multi-vitamin and I said I did, a daily Centrum.
She told me to stop taking it. I have never had elevated liver enzymes in the 15 years since. She told me overdosing on some vitamins was causing live damage as my liver struggled to process them.
Now that said, it's not clear to me that it's causitive, since usually when I stop taking my dose, it's because I've run out, and it's very possible my not having time or interest to get more means I may have already started down the depressed path, and I may already be recovering when I finally start taking care of myself.
In any event I don't seem to get the really dark depressions I got before taking d3 and I don't dare stop taking it intentionally. Even if it's largely placebo the cost and risk seem very small conpared to my perceived benefits.