What studies confront the idea that iron is associated with cancer?
Another clinical study, performed on 733 participants, published in 2000 suggested body iron stores isn’t associated with recurring incidences of colorectal adenoma. Similar to the previous study, participants submitted a questionnaire where they estimated their intake and usual portion sizes of specific foods over the previous year. To measure body iron store levels of serum ferritin were determined. This was done by extraction of venous blood from subjects on enrolment, and a blood chemistry panel is performed. Serum ferritin levels were determined via IMx ferritin assay kits. 269 subjects developed recurring adenomas between years 1 and four. However, the study concluded there was no clear association between the level of serum ferritin and recurrence of adenomas. These findings suggest body iron stores are not highly significant in the role of developing colorectal cancer.
Another study which supports the negative relationship between body iron levels but the positive relationship between high dietary iron intake and the development of colorectal cancer was a nested case-control study in the New York University Women’s Health Study cohort. With an average follow up of 4.7 years there was 105 reported cases of colorectal cancer, with 523 matched controls using starting levels serum iron, ferritin, transferrin saturation, and total iron binding capacity. They were identified through blood samples and used to determine body iron stores. Supplement intake and diet were assessed via questionnaires to find the estimated total iron intake. The study found no link between the risk of serum groups and colorectal cancer, apart from serum ferritin, which displayed an inverted relationship.
Interestingly, it did find a considerably increased risk of high total iron intake and colorectal cancer with an odds ratio of (OR) = 2.50; 95% confidence interval (CI) when combined with a high-fat diet. This could be the case because a considerable amount of dietary iron isn’t absorbed in the body and therefore gets concentrated into feces within the intestine. A diet high in fat also allows intraluminal peroxidation reactions to occur (which are catalyzed by iron) due to the abundance of lipid substrate.