Research in this field engaged in scientific experts from the Technical University of Chalmers. They found that citrate of iron and trivalent iron in the form of hultanas can cause the development of colon cancer. These compounds stimulate the formation amphiregulin — a protein whose level is often increased in malignant tumours of the intestine. But the sulphate of iron does not have that effect.
In the end, scientists recommended people not to abuse the iron, and to give preference to natural products which contain this trace mineral. In particular, should eat more vegetables, fish, meat and whole grain products.