Re: if you have cancer or dont want cancer...

The best form is natural  D3 from the sun.  That is not always possible - especially in winter months in northern climes.  I use a product from Biotech which I get from Utopia Silver (and use the discount code of LR001 to get 15% when it is not on sale).  I get lots of sun and so do not find it necessary to supplement very day with Vitamin D3, but I would opine that 3000 to 5000 mg a day would be an optimum amount, especially when fighting or preventing cancer.

All the best,

Tony