multiple sclerosis is more prevalent in areas with less sun (basically in the north, since not many people live at low southern latitudes).

i have ms and vitamin d is suspected to be important in reducing the chance of suffering from that disease (it's an immunomodulator - has some connection with your immune system - and ms is basically your immune system attacking your own nerves). other risk factors include being a woman, and having had glandular fever or chickenpox (or both). i am prescribed quite high doses (about double what i see as recommended for supplements). i understand that, along with the medication i take, it helps reduce further outbreaks.

i found it kind of weird that this kind of knowledge is still ongoing research. seems like the kind of thing people would have worked out by now.

anyway, consider getting a little sun each day (according to http://www.nhs.uk/Livewell/Summerhealth/Pages/vitamin-D-sunl... you don't need long), and maybe a supplement in winter, if you're in the north.