Dietary Intake of Vitamin B12 in Relation to Diet and Lifestyle Characteristics in a Population at High Risk for Colorectal Cancer

By Banjari, Ines; Kožić, Snježana | Central European Journal of Public Health, December 2018 | Go to article overview

Dietary Intake of Vitamin B12 in Relation to Diet and Lifestyle Characteristics in a Population at High Risk for Colorectal Cancer


Banjari, Ines, Kožić, Snježana, Central European Journal of Public Health


INTRODUCTION

Colorectal Cancer - Epidemiology and Recent Insights

Colorectal cancer (CRC) is distinctive for its strikingly high correlation with diet (1). Incidence rates have changed significantly (2) but it remains the third most common cancer globally, with high mortality if diagnosed in later stages and immense impact on public health (3, 4). In Croatia, CRC is the third most common cancer in men and the second in women (5). Incidence of CRC drastically increased between 1990 and 2013; 175% for males and 125% for females (6), with mortality rate of around 66%, regardless of gender (5). Still, large variations in CRC incidence across Croatian regions (5, 6) are attributed to large differences in dietary patterns across Croatia (7).

Dietary and lifestyle risk factors for CRC are well known (8). Currently, the strongest positive association with CRC risk was found for intake of red and processed meat (2). However, omitting meat and meat products from diet means eliminating highly valuable sources of protein, iron and vitamin B12 (9).

Vitamin B12 - Body Homeostasis and Dietary Sources

As the largest and most complex vitamins of all, vitamin B12 plays an irreplaceable role in human health; from one carbon (C-1) metabolism, through epigenetic alterations related to gene expression and related risk of cancer, neurodevelopment and cognition, and foetal programming via maternal nutrition, to metabolism (including hyperhomocysteinemia, adiposity and insulin resistance) (10-12).

Along with other B complex vitamins (folate, vitamin B6 and B2), vitamin B acts as a co-enzyme in a network of interrelated biochemical pathways that donate and regenerate C-1 units, affecting folate-dependant reactions and mitochondrial energy and lipid metabolic pathways (10). Normal C-1 metabolism enables DNA replication, DNA repair, and regulation of gene expression (12), which is why vitamin B12 started to raise interest within the scientific community in the area of cancer research. Vitamin B is often compared with folate and considered to have positive effect in C-1 cancer-related alterations, like in CRC (13-15).

Naturally, vitamin B12 can be found only in foods of animal origin, such as meat, poultry, fish (including shellfish), and to a lesser extent in milk and dairy (16, 17). Importantly, vitamin B from these dietary sources has the highest bioavailability (between 40% and 89%) (7). Besides vitamin B12, meat, especially red meat, is a valuable source of other B complex vitamins like niacin, thiamine, riboflavin, and pyridoxine (9), which can also be found in high amounts in fish and milk and dairy products. All of these B vitamins have immense importance in maintaining a normal C-1 metabolism (12-14).

Nowadays, vitamin B12 can be found in a wide variety of fortified foods, especially in cereal products (e.g. breakfast cereals). With numerous pros (and cons), fortification with vitamin B remains to be voluntary in most countries around the world (Croatia is among countries that do not have mandatory fortification with vitamin B12). However, even in countries with such measures in force, vitamin B12 deficiency prevalence is high (16, 17). Supplements also need to be considered when estimating total intake of vitamin B12 (16, 18). Population groups at risk of low intake of vitamin B12 include elderly, children and infants, and vegetarians and vegans (10).

In food, vitamin B12 is bound to protein, and its absorption asks for a normal gastric activity i.e. production of gastric pepsin and acid. Three proteins have the ability to bind vitamin B12 and will ensure its optimal absorption: haptocorrin, intrinsic factor (IF) and transcobalamin (1, 10). Any disturbance in the gastrointestinal system (due to medications, acute or chronic inflammations, etc.) can impair vitamin B12 status of an individual (11).

Vitamin B12 and Carcinogenesis

Vitamin B12 has been proposed as a potential cytoprotector in terms of neoplasms of the bowel (19). …

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