Here's a good article, PV is opposite of anemia basically, this article explains what to eat to produce more red blood cells so its foods to limit if you have PV..
https://www.verywellhealth.com/how-to-increase-red-blood-cells-5211834#:~:text=Vitamin%20B12%20helps%20the%20body,fish%2C%20dairy%2C%20and%20eggs.