There are factors influencing non-heme iron absorption itself. Among these are tannins in tea and coffee. Phytates in whole grain bread, milk proteins, albumin and soy proteins may also reduce absorption. This means that a regular diet and non-heme supplements may not be enough to compensate for iron loss. Heme iron absorption is not affected by any of these factors.
Non-heme supplements at 100 mg iron per dose regularly have an incidence of side- effects leading to termination of the therapy of around 30 %. Donors that have previous negative experiences will usually not take the supplements at all.