when i was tested i was at about your level. it took 6 months of 10,000 ius daily to get up to "normal". i live in new england.
mark's recs are maintenance dosage for people already at a healthy level.
As I ate the oysters with their strong taste of the sea and their faint metallic taste that the cold white wine washed away, leaving only the sea taste and the succulent texture, and as I drank their cold liquid from each shell and washed it down with the crisp taste of the wine, I lost the empty feeling and began to be happy and to make plans.
– Ernest Hemingway