I am pale as all heck and slather on copious amount of sunscreen all the time no matter what—down here in Southern California. However I test exceedingly high for sun caused vitamin D absorption. I beleive this is because I jog about an hour 5 or so days a week (or atleast used to before I met my beloved FR—lol), however I wear one of those Sunbrella (? or some brand like that) hats with a wide rim and neck protector to protect my skin as well as all the sunscreen mentioned above.
So I think getting out for any type of outdoor exercise on a consistant basis with protection is probably optimal. But one can also do Vitamin D tablets. If prescribed by a doctor you will only have to take it only once a month which is nice, if one can remember to take the silly thing :-).