I used to have very rough winters. Despite the fact that I ate well and was outside 2+ hours every day. I got my blood tested and I had very low vitamin D, two tiers below normal. This was the first winter being on Vitamin D, and my energy and hunger levels stayed normal. I never crashed or had extreme hunger or trouble sleeping.

Getting Vitamin D from food is a fools errand, and since sunscreen and protective clothing slow vitamin D from the sun drastically, it's in most people's best interest to get it tested.