[repsak]

To add some anecdotal evidence... We basically get no sun for half of the year where I live. I find my subjective wellbeing has increased somewhat, especially during the winter months, since I started supplementing with 5000UI D3.

Other potential benefits are harder to measure, but the cost in terms of money and likelihood of adverse effects is so low I feel I might as well continue.

To add another data point, gwern has done some more rigorous self experiments https://www.gwern.net/zeo/Vitamin-D