Vitamin D will help but it is not the only beneficial compound produced by our skin in the presence of sunlight. Strategic tanning bed/booth & Vitamin D supplementation works best imho.

There seems to be attitional benefits to the sunlight induced vitamin D production, possibly related to the oxidation of cholesterol & sulphur as the cholesterol is converted into Vitamin D.

While Vit D helps me, additionally using a 10k lamp is like night and day, if you forgive the pun.

This was my experience as well. For two years I lived at a latitude where I got about zero daylight for 5-6 months per year. My SAD-lamp helped a little (<10k lumens), vitamin D helped a lot.

How much Vitamin D did you take? Did you measure/calc the amount per kg?

From research around the Internet, D3 is generally seen as safe (http://www.mayoclinic.org/drugs-supplements/vitamin-d/safety... is pretty typical on the safety information) Personally I take a D3 supplement of 2000IU/day during the dark months (along with some other supplements due to a mostly vegan diet, some of which contain low D2/D3 amounts, so my actual supplemented intake is around 2400 IU).