"You CAN get a simple blood test, with recommended levels, if you ask your doctor. The results can help you decide how much Vitamin D you should be taking.
My doc, deciding I'm the kind of guy who likes this kind of stuff, ordered it, and told me, "You're the first patient I have that has the correct level -- how much Vitamin D do you take? What brand?"
I take 5000 units per day, and I get Puritan's Pride brand, or Piping Rock, whichever is on sale. Good for bones, good for depression, what else?"
- Bill C.
Response: Breast cancer. It correlates favorably with sunlight and vitamin D intake. Women doctors I know take 15K iu/day. Rare in the tropics it goes up as you move away fro the equator.
This has been known for ages. See Harold Foster's last book on cancer.
Halibut liver oil is the best source, it's a tad more potent than cod liver oil but the same stuff. You don't want the chalky pills, it's the wrong form and doesn't work nearly as well if at all.
D has complicated chemistry.