You have told us that 5000 IU of vitamin D3 taken twice a day would be safe and helpful for many, many people. Is that enough to get serum levels in a useful range for cancer prevention?

This will be true in most cases and is consistent with our recommendation that people are underexposed and undernourished when it comes to vitamin D in their body, and that is because medical science has been misled about the great importance of this vitamin for many bodily functions and the corresponding health outcomes when blood levels are too low for too long a time.