How our genes influence our coffee habits
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For some, a source of energy, but for many, a morning ritual before seizing the day. No matter what it is, coffee has become a daily staple for countless Canadians. In fact, it has become the most consumed substance with a psychoactive property (via the effect of caffeine), with 71% percent of Canadians consuming coffee every day. However, this could greatly vary between individuals, with some choosing to consume a lot more coffee than others.
Interestingly, whenever there is variability in any behavioural trait, such as coffee consumption, scientists become interested in one question: Could this variability be influenced by our genetics, and how? Previously, it was shown that there is some genetic component to daily coffee intake; but what can we learn about other traits from examining the genes that influence our coffee consumption? To tackle this question, a study was led by Dr. Hayley Thorpe, a post-doctoral researcher at Western University, in collaboration with colleagues across the US, UK, and the Netherlands.
Genome-Wide Association Studies (GWAS)
The study used US-based participants in the genetic testing company 23andme that consented to take part in a genome-wide association study (GWAS) and answered a questionnaire regarding their coffee consumption and other health traits. In a GWAS, scientists examine the genome (i.e., the complete set of genetic material of a living being) of many individuals to look for genetic variations and try to correlate these variations with a clinical condition or a behavioural trait. To further validate the results, the US-based data was compared with the largest available GWAS study on coffee consumption conducted in the UK.
Coffee consumption and the brain
This genetic study identified many genes that were correlated with coffee consumption, meaning those who consumed more coffee are more likely to have specific variations in those genes. Many of those genes appeared to be highly relevant in the brain and were shown to be present across different brain regions. This indicates that differences in coffee consumption could be partially attributed to differences in the genetics that shape our brains. In agreement with these findings, the authors of the study also point to previous research that showed differences in the brains of those who regularly drink coffee compared to those who do not.
The good, the bad, and the unexpected of coffee consumption
While previous studies on coffee consumption have shown associations with many positive benefits that include lower risks of cardiovascular disease, neurogenerative disease, and some cancers, the current study only found consistent genetic correlations with adverse outcomes. More specifically, genetic associations were observed with substance use (i.e., smoking initiation, cannabis initiation, drinks per week) and obesity-related traits in both the US-based and the UK-based GWAS. However, correlations with other traits appeared to be inconsistent between the US-based and the UK-based data. Interestingly, it was previously known that the use of one substance could increase the likelihood of the use of another, for example, the increased likelihood of smoking cigarettes in those who also drink alcohol. The results of this study indicate that coffee consumption is not safe from this generalization, as there is a correlation between coffee consumption and substance use.
These results may scare some of us coffee enthusiasts, however, the authors also highlight the caveats of these types of studies. One such caveat is the difference between correlation and causation, where two traits may be present together but do not directly influence each other. Other caveats include the limited population surveyed, who are all of European descent, or the fact that it is difficult to control for other habits that surround coffee consumption such as eating or smoking. Additionally, while both populations were of European descent, there were clear differences between the results from the US-based and the UK-based GWAS, which highlight the importance of culture and environment on our habits. An example of this is the increased intake of caffeine through tea consumption in the UK population, which may have influenced the data.
Overall, the results of this study provide us with more insight into how even the simplest of our daily habits, such as our coffee consumption, can be influenced by our genetics. However, this study also shows us that there is more complexity to these habits beyond our genetics, as our environments and cultures also play a role. Although scientists are always interested in how our genes shape us on a population level, these studies provide a constant reminder that, on an individual level, it is near impossible to unwind the eternal braid that is our nature and nurture.
Original Article: Thorpe, H. H. A., Fontanillas, P., Pham, B. K., Meredith, J. J., Jennings, M. V., Courchesne-Krak, N. S., Vilar-Ribó, L., Bianchi, S. B., Mutz, J., 23andMe Research Team, Elson, S. L., Khokhar, J. Y., Abdellaoui, A., Davis, L. K., Palmer, A. A., & Sanchez-Roige, S. (2024). Genome-wide association studies of coffee intake in UK/US participants of European ancestry uncover cohort-specific genetic associations. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 49(10), 1609–1618. https://doi.org/10.1038/s41386-024-01870-x