I agree with a few other people here. Getting outside for a hike or walk around the neighborhood multiple times a week even in the winter months helps a lot, even on the overcast days. This winter it was pretty easy considering how mild it was. Don't get me wrong I have days where I think about visiting my in laws in Florida but for the most part getting outside helped a lot. I also increased the lighting throughout my house to make things brighter when indoors.

​

Edited to add, its not bad getting outside in the winter with proper layers. Base, mid layer, outer layer. Try not to wear cotton. Stick to Merino Wool, synthetics, fleece and a decent outer layer and you'll be comfortable especially once you get moving.