I've had first-hand experience of something that's been discussed elsewhere: a lack of omega 3 fatty acids and vitamin D3 itself may be associated with heavy sunburns and sun allergy (itchy skin, runny nose etc right as you're out in the sun, and not caused by fragrances or cold air).

I'm not able to look up studies for this right now so I'm just going by my own experience and other anecdotal reports, but it's a kind of circular dependency that intrigues me.