Plant-based sources of dietary iron may reduce colorectal cancer risk in men

Iron in our diet comes from either animal (heme) or plant-based (non-heme) sources. Researchers have analysed data from a large European study involving 450,105 people from 10 countries over a 14 year period to see if dietary iron intake is linked to a risk of developing colorectal cancer.

Meat, poultry, seafood and fish are sources of heme-iron. Non-heme iron is only found in plant-based foods like nuts, grains, vegetables, and fruit.

Findings published in the British Journal of Cancer suggest that dietary, non-heme iron may reduce colorectal cancer risk in men. However, dietary iron, irrespective of the food sources, does not seem to influence colorectal cancer risk in women. This may be due to overall lower iron intake in women, or reproductive and hormonal factors.

Dr David Hughes, UCD School of Biomolecular & Biomedical Science and Fellow, UCD Conway Institute explains, “We specifically conducted our analyses separately in men and women because they have different iron needs, intake patterns, absorption rates, turnover, and excretion in the body, which could possibly lead to cancer risk differences.

In men, we did not see any relationship between intake of total iron and colorectal cancer risk. However, higher intake of non-heme iron was associated with 20% lower colorectal cancer risk.

In our study models, colorectal cancer risk reduced by 6% in men by replacing daily intake of 60 mg of cooked beef (1 mg heme iron) with 30 g of boiled beans or two boiled eggs (1 mg non-heme iron).

By contrast, in women we did not find any association between total, heme, or non-heme iron on colorectal cancer risk.”

Researchers also looked at whether iron may be associated differently for colorectal tumours according to their location. They found that heme iron was associated with a higher risk of tumours in men that occurred in the rectum and the proximal colon (portion of the colon going up and across the abdomen) compared to the distal colon (portion of the colon that goes down towards the rectum).

There was no clear explanation of why the associations observed in men were stronger in the rectum and proximal colon. This difference according to anatomical location was not seen in women.

Colorectal cancer is one of the most common cancers globally, with over 1.9 million individuals diagnosed in 2020. There is a growing understanding of the risk factors for colorectal cancer. Higher consumption of red and processed meats increases the risk of developing a tumour in the colorectum.

Researchers do not fully understand why heme iron contained in meats promotes colorectal cancer. One possibility is that heme iron is involved in producing DNA-damaging free radicals. Non-heme iron is chemically different and does not fuel the production of free radicals.

Iron deficiency is a public health issue in several countries. This analysis focused on a European population where iron intake is relatively high. The data included 450,105 participants from 10 European countries (318,680 women), recruited in 1990s and followed for over 14 years.

The findings may not be generally applicable especially in settings where iron intake is low or where lifestyle choices such as drinking tea during food time, repeated infections, or low intakes of vitamin C impacts on how iron is taken up and used in the body.

The published article is available online: Aglago EK et al. Dietary intake of total, heme and non-heme iron and the risk of colorectal cancer in a European prospective cohort study. Br J Cancer. 2023 Feb 9. doi: 10.1038/s41416-023-02164-7. Epub ahead of print. PMID: 36759722.