Variations in a gene called FUT2 may have small but important effects on a person’s ability to digest, absorb, and use vitamin B12, according to research published online in the journal Nature Genetics.
"The news here is the discovery of a robust genetic predictor of vitamin B12 levels," said lead researcher Professor David Hunter from the Harvard School of Public Health. "This is an example of the way we're going to understand more about how levels of vitamins and other nutrients in the body are partially determined by genetic factors as well as by what we eat."
Hunter’s co-worker, and lead author of the study, Aditi Hazra added: "This provides a framework for further nutrigenomics studies and for exploring gene-diet interactions with cancer and other diseases."
Nutrigenomics is defined as how food and ingested nutrients influence the genome (personalised nutrition). Nutrigenetics is defined as how a person's genetic make-up affects a response to diet (individual nutrition).
Vitamin B12 levels are important as low levels of the vitamin have been linked to increased risk of cognitive impairment and neurodegenerative disorders, cardiovascular disease, and certain types of cancer. Up to 25 per cent of the elderly may be B12 deficient.
In the diet, B12 comes from meat, fish, dairy, other animal products, and fortified breakfast cereals. Vegetarians and vegans are also at risk of B12 deficiency.
The Harvard researchers, in collaboration with scientists at Tufts University and the National Cancer Institute (NCI), identified FUT2 from a genome-wide scan of 1,658 women of European ancestry who participated in the Cancer Genetic Markers of Susceptibility (CGEMS) project. The results were replicated in another 1,059 women from the Nurses' Health Study.
An evaluation of more than 528,000 genetic variants showed that rs492602 FUT2 had the greatest effect on B12 levels – about three per cent of the variation. However, no direct evidence exists currently that people who carry the gene variant suffer from any cognitive or other adverse affects of low B12 levels.
On the flip side, a variation of the same gene that is associated with the highest B12 levels has also been linked to protecting the stomach from infection by the Norwalk virus and ulcer-causing H. pylori bacterium.
"This is an unexpected finding. We thought we had already learned everything about the absorption of vitamin B12," said co-author Jacob Selhub from Tufts University.
Previous studies have suggested that anything that changes the normal acidity and digestive processes of the stomach may also have an impact on B12 absorption. This is because B12 separation from food first occurs in the stomach before being carried by a protein to the small intestine for absorption.
Preventing B12 malabsorption by protecting against H. pylori infection, for example, appears to be the most plausible explanation for the potential preventive effect of the gene variant, said the researchers. However, further studies are needed to clarify this.
This study was supported by the National Cancer Institute of the National Institutes of Health.
Source: Nature Genetics Published online ahead of print, 7 September 2008, doi:10.1038/ng.210"Common Variants of FUT2 are Associated with Plasma Vitamin B12 Levels”Authors: A. Hazra, P. Kraft, J. Selhub, E.L. Giovannucci, G. Thomas, R.N. Hoover, S.J. Chanock, D.J. Hunter