The best thing that I have found for dealing with polycythemia vera has been to adhere to a very low carb diet. When I am in nutritional ketosis I feel much better and the time between my phlebotomies increases from roughly once every four weeks to up to five months between phlebotomies. Your mileage may vary, and before starting a diet like that I would strongly encourage you to meet with your physician and make sure it is safe for you. A keto diet is definitely not something you can do if you are Type 1 diabetic!