Researchers analyzing data from hundreds of thousands of people uncovered genetic factors that influence how often we go to the bathroom, with a surprising spotlight on vitamin B1.
Bowel habits may not come up often in everyday conversation, but they offer important clues about how quickly the digestive system moves food through the gut. When this process slows down or speeds up too much, people can develop constipation, diarrhea, or irritable bowel syndrome (IBS). Despite how common these problems are, scientists still do not fully understand the biology that controls bowel movements.
A new study published today (January 20) in the scientific journal Gut sheds light on this mystery by uncovering genetic factors tied to intestinal movement and highlighting vitamin B1 (thiamine) as a surprising area for future research.
A Large Genetic Study of Gut Movement
The research was led by an international team coordinated by Mauro D’Amato, Professor of Medical Genetics at LUM University and Ikerbasque Research Professor at CIC bioGUNE, member of BRTA.
The scientists used a large-scale genetic analysis to look for common DNA differences linked to how often people have bowel movements, a measure referred to in the study as stool frequency. To do this, they analyzed genetic data and health questionnaires from 268,606 individuals of European and East Asian ancestry. Advanced computer-based methods were then used to identify genes and biological processes most likely to influence gut movement.
Known Gut Pathways Confirmed by Genetics
The researchers identified 21 regions of the human genome associated with how frequently people open their bowels, including 10 regions that had not been reported previously. Many of these genetic signals pointed to biological pathways already known to play a role in gut movement, which helped validate the findings.
Among them were bile-acid regulation (bile acids help digest fats and also act as signaling molecules in the gut) and nerve signaling involved in intestinal muscle contractions (including acetylcholine-related signaling, which helps nerves communicate with muscle). These results align with existing knowledge of how the gut functions.
Vitamin B1 Emerges as a Key Signal
The most unexpected finding appeared when the team focused on two high-priority genes tied to vitamin B1 biology. These genes, SLC35F3 and XPR1, are involved in how thiamine is transported and activated in the body. To see whether this genetic signal had real-world relevance, the researchers examined dietary data from the UK Biobank. Among 98,449 participants, higher intake of dietary thiamine was linked to more frequent bowel movements.
The relationship was not the same for everyone. The effect of vitamin B1 intake depended on a person’s genetic makeup at the SLC35F3 and XPR1 genes (analyzed together as a combined genetic score). This suggests that inherited differences in how the body handles thiamine may influence how vitamin B1 affects bowel habits across the population.
Links to IBS and Future Research Directions
Dr. Cristian Diaz-Muñoz, the study’s first author, explained the significance of the findings, saying “We used genetics to build a roadmap of biological pathways that set the gut’s pace. What stood out was how strongly the data pointed to vitamin B1 metabolism, alongside established mechanisms like bile acids and nerve signaling.”
The study also points to a shared biological basis between bowel movement frequency and IBS, a condition that affects millions of people worldwide. “Gut motility problems sit at the heart of IBS, constipation, and other common gut-motility disorders,” says Prof Mauro D’Amato, “but the underlying biology is very hard to pin down. These genetic results highlight specific pathways, especially vitamin B1, as testable leads for the next stage of research, including lab experiments and carefully designed clinical studies.”
Reference: “Genetic dissection of stool frequency implicates vitamin B1 metabolism and other actionable pathways in the modulation of gut motility” by Cristian Díaz-Muñoz, Isotta Bozzarelli, Esteban Alexander Lopera-Maya, Lazaros Belbasis, Valeria Lo Faro, Leticia Camargo Tavares, Francisco Heredia-Fernández, Biagio Di Lorenzo, Trishla Sinha, Cristina Esteban Blanco, Marie-Julie Favé, Philip Awadalla, Robin G Walters, Ferdinando Bonfiglio, Alexandra Zhernakova, Serena Sanna and Mauro D’Amato, 20 January 2026, Gut.
DOI: 10.1136/gutjnl-2025-337059
The study was led by Mauro D’Amato’s Gastrointestinal Genetics Research Group and involved investigators from CIC bioGUNE in Spain, LUM University, Institute for Genetics and Biomedical Research – CNR, CEINGE and University of Naples Federico II in Italy, University of Groningen in The Netherlands, University of Oxford in UK, Concordia University and Ontario Institute for Cancer Research in Canada, and Monash University in Australia. The research was supported by grants from MCIU/AEI/10.13039/501100011033 and ERDF/EU (PID2023-148957OB-I00); PRIN2022/NextGenerationEU (2022PMZKEC; CUP E53D23004910008 and CUP B53D23008300006); ERC Starting Grant (101075624); PNRR/NextGenerationEU (PE00000015/Age-it); NWO-VICI (VI.C.232.074); NWO Gravitation ExposomeNL (024.004.017); EU Horizon DarkMatter program (101136582).
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