We hardly get sun here. Got a depression last fall, probably lack of vitamin D. Been staying on top of getting supplements.
Need UVB light on your skin for vitamin D, and you need blue light in your eyes for helping with seratonin levels. Both are key. I got a SAD lamp at work I use in the morning or at the start of a night shift.
The one thing I don't like about winter is how it's dark all the time. It never actually affected my mental health, but it did last year, so it's something I try to be more aware of now. On my days off I try to get up earlier so I can catch some natural day light and bundle up and go for a walk. Have not been doing it as much as I should though. On days where I work, well I don't see any daylight at all so just have the SAD light.
Sooo glad it's well above freezing most of the winter here, so I can expose more skin to the sun .
I've noticed "zinc methionine sulfate" REALLY boosts neurotransmitter production in the brain, when paired with 5HTP or tryptophan, so it must be critical for the process. Taking Zinc on its own isn't as detectable, neurotransmitter-wise, but it's still vital no doubt. I'd consider supplementing with magnesium, calcium, D3, and zinc (balanced w/ copper) when afflicted with depression / SAD.
Something I learned yesterday: Low D results in impaired calcium absorption, and calcium is needed to convert tryptophan to melatonin, so with low calcium, you're less likely to achieve REM sleep (due to low melatonin).
I've dealt with chronic insomnia for years, so I've come to value vitamins/minerals to keep me sane. There's an underlying injury, so for me it's more complicated than simple nutrition and behavior.