If you are getting blood tests to check vitamin levels, and it says "no supplements 24 hours", can you still have Tums (calcium carbonate) if not checking calcium levels?

I guess so. Blood vitamin levels can be very deceptive. You can have normal levels and still be deficient because it is the vitramin content within cells that really counts. Vitamin therapy and basic understanding of its uses is largely in the hands of doctors that practice complementary alternative medicine. Homeopathists, naturopath doctors and cheiropracters are often knowledgeable in this field.