Something I only learned recently is that sunshine alone doesn't necessarily guarantee vitamin D, there are peak times during the day where your body is able to get more vitamin D. This is usually centered around midday, or 11 am to 2 pm (with a little bit wider window closer to summer.) Outside of those hours you actually don't get a whole lot of vitamin D. When I am low on vitamin D I feel sluggish/fatigued and more anxious/depressed. Supplements help but I have heard claims that a supplement doesn't give you the whole benefits of sunlight and/or vitamin D. Vitamin D is hard to get in foods. Fish has a bit, and foods that have been fortified with it.