Bacteria, vitamins, and your DNA: How are they related?

The world is covered with bacteria, and so are we. Different types of bacteria colonize multiple areas both on and within the human body, which collectively impact human health. Vitamin absorption is one area where bacterial composition in your body can have an influence. Whether that influence is positive or negative may be affected by your DNA, specifically whether you’ve inherited variants within the FUT2 gene.
The gut microbiome is a diverse and complex ecosystem comprised of literally trillions of microbes1. Several factors can influence the types of bacteria that grow inside of you, including your diet, environment, and genetics. The collection of bacterial species within your gut—also known as the gut microbiome—can actually be beneficial for human health because these bacteria help support nutrient metabolism in various ways and have been associated with decreased susceptibility to certain gastrointestinal disorders1,2. A variant of the FUT2 gene is associated with both a change in the gut microbiome and a predisposition to having decreased levels of vitamin B121-4.
By definition, vitamins are nutrients that are vital to our health but cannot be synthesized by our body. Because our body can’t produce them, we have to get them in our diet. Vitamin B12 is no different: it’s required for important molecular processes which are involved in blood cell synthesis, development and maintenance of the nervous system, and DNA synthesis, among other things3,5. Many vitamins can be found in vegetables and fruits, but B12 is predominantly found in animal products like fish, poultry, beef, and eggs5. When we consume foods with B12 in them, a network of proteins are involved in capturing the vitamins in our gut, bringing them in, and distributing them throughout the body.

FUT2 is an indirect player in this process. This gene produces a protein that helps attach a type of sugar known as fucose to carbohydrates in the mucus layer of our intestines1,2. Like humans, bacteria consume sugars, and the sugars in our intestinal mucus layer provides a veritable buffet—ultimately helping the microbiome ecosystem. Disruption of this food source may also disrupt the types of bacteria that colonize the gut. It’s thought that placement of fucose in the mucosal layer contributes to our immune response by enabling “good bacteria” to colonize the gut in place of “bad” bacteria. Evidence for this comes from studies that show a lack of the FUT2 protein is associated with increased gastrointestinal infections from various pathogens1,2.
Distinctly different from total loss of the protein, there are many people who inherit a version of the FUT2 gene that is slightly altered3,4. This variant has been associated with the levels of B12 circulating in a person’s body. It’s not entirely clear how FUT2 influences vitamin B12 levels, but there is some evidence to suggest it has something to do with the gut microbiome and the body’s ability to absorb vitamin B123,4. Although we don’t know why, studies have repeatedly shown that individuals who inherit one version of the gene (you might see it called the G allele, or in scientific papers it will be referred to as the rs602662 variant) are likely to have decreased levels of vitamin B12 relative to those without it1-4. (It’s important to note that this association is with decreased levels of vitamin B12, but not with a vitamin B12 deficiency.)
If you’re curious to see how your genetics may be influencing your body, there are several DNA tests that analyze your genome and provide you with insights about how your body likely processes certain foods. One such product is EverlyWell’s Food Sensitivity+ DNA test, which analyzes your FUT2 gene and provides feedback regarding your predisposition for decreased levels of vitamin B12, in addition to numerous other insights. Personalized information like this can help you understand how your body processes certain nutrients.

1Kashyap, Purna C. et al. “Genetically Dictated Change in Host Mucus Carbohydrate Landscape Exerts a Diet-Dependent Effect on the Gut Microbiota.” Proceedings of the National Academy of Sciences of the United States of America 110.42 (2013): 17059–17064. PMC. Web. 21 Dec. 2017.
2Wacklin, Pirjo et al. “Secretor Genotype (FUT2 Gene) Is Strongly Associated with the Composition of Bifidobacteria in the Human Intestine.” Ed. Michael Otto. PLoS ONE 6.5 (2011): e20113. PMC. Web. 21 Dec. 2017.
3Tanwar, Vinay Singh, et al. “Common variant in FUT2 gene is associated with levels of vitamin B12 in Indian population.” Gene, vol. 515, no. 1, 29 Nov. 2013, pp. 224–228., doi:10.1016/j.gene.2012.11.021. Web. 21 Dec. 2017
4Tanaka, Toshiko et al. “Genome-Wide Association Study of Vitamin B6, Vitamin B12, Folate, and Homocysteine Blood Concentrations.” American Journal of Human Genetics 84.4 (2009): 477–482. PMC. Web. 21 Dec. 2017.
5Degnan, Patrick H., Michiko E. Taga, and Andrew L. Goodman. “Vitamin B12 as a Modulator of Gut Microbial Ecology.” Cell metabolism 20.5 (2014): 769–778. PMC. Web. 21 Dec. 2017.