Dietary sources of iron and vitamin B12: Is this the missing link in colorectal carcinogenesis?
Introduction
Colorectal cancer (CRC) remains the third most common cancer around the globe. Even though incidence rates have dropped significantly in some countries [1], they are still high and the incidence continues to rise among those aged <50 years [1], [2]. Hereditary CRCs account for 10–30% of all cases, while the remaining 70% are sporadic CRCs [3], [4]. Early diagnosis is crucial as CRC is fatal in almost half of the cases if diagnosed in later stages [2], [5].
CRC is the cancer with the most convincing correlation with the diet [6], and lifestyle and dietary habits overcome genetic predisposition and diagnosis of inflammatory bowel disease [7]. So far, the strongest positive association with CRC risk has been found for intake of red and processed meat [1]. However, meat and meat products are important dietary sources of both iron and vitamin B12, and omitting these foods from the diet can lead to iron and vitamin B12 deficiency (e.g. in vegetarians and vegans) [8], [9]. The evidences supporting strong positive relation between heme-iron from red and especially processed meat and CRC risk [10], are not as clear for either total dietary intake of iron [11], [12], [13], [14], [15], [16], [17], [18] or vitamin B12 intake [17], [19], [20], [21], [22], [23], [24]. Having in mind immense importance that iron has for the overall body functioning, clarifying the relevance of various dietary sources of iron in CRC risk is of great importance.
Section snippets
Hypothesis
We hypothesize that specific combinations of foods of animal origin could alter the risk of CRC, and even modulate the progression of CRC. In other words, by specifically designing a diet in a way that specific food groups supply sufficient amounts of iron and vitamin B12, potentially detrimental effects of high amounts of iron in the lumen of the large bowel can be diminished.
Basis for the hypothesis
Vitamin B12 has been proposed to have a cytoprotective effect, i.e. protecting enterocytes in the bowel from neoplasms [25]. Kurbel et al. [25] compared incidence rates of gastrointestinal cancers, across the segments of the bowel while considering the difference in absorption and availability of separate nutrients and their presence in the bowel. The analysis of separate segments of the bowel showed that vitamin B12 is the only nutrient unavailable for absorption in the large bowel, i.e. the
Conclusion
We are yet to find the underlying effects of iron and vitamin B12 on CRC. Better designed human studies are needed to determine the real association between the total dietary intake of iron, not only heme iron and CRC risk [11]. The cytoprotective effect of vitamin B12 along with a diminished effect of high iron intake content in the feces through reduced bioavailability gained by high contribution of milk and dairy with highly bioavailable vitamin B12 seem worth exploring more thoroughly. It
Funding
There was no financial or material support for the work.
Conflict of interest statements
None of the authors (IB, AH) have no conflict of interest to declare.
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