Caucasian male (age 35) with melasma... I would like to know why?

Hello all. From the research I've done, I seem EXCEPTIONALLY rare, and I cannot figure out what has caused my melasma. I am a 35 year old caucasian male, and was diagnosed with it several years ago by a dermatologist. I have never spent excessive amounts of time in the sun (I live in the UK, we don't get much of it!), and I am fit and healthy with no other health issues.I have it above my eyebrows and around and below my eyes. It is not excessively dark as I have seen some examples of, but it is bad enough that I feel the need to wear make-up to cover it up, as I am very self conscious about it.I would very much like to know what the possible causes might be. Over the past few years I have changed my diet completely... not that it was ever unhealthy, but I had read about copper levels etc. so made several changes. I have also tried various supplements, but nothing has helped. I wear factor 30 sunscreen EVERY DAY. Fortunately it hasn't really got much worse, but I find it a constant burden and at the very least I would like some answers. A part of me also can't help but wonder that given I seem such an unlikely candidate for melasma in the first place, their MUST be an explanation for it, and therefore something that can be done about it??