New evidence from more than 266,000 UK adults reveals that working permanent night shifts can disrupt the body’s internal clock, alter gut function, and heighten the risk of irritable bowel syndrome. This finding could reshape how we view shift work and digestive health.
Study: Night shift work increases the risk of developing irritable bowel syndrome: a prospective cohort study in the UK Biobank. Image credit: ultramansk/Shutterstock.com
A new study published in Frontiers in Public Health found that working a permanent night shift can increase the risk of irritable bowel syndrome.
Background
Irritable bowel syndrome is a gastrointestinal disorder characterized by abdominal pain, abdominal bloating, and irregular bowel habits such as constipation and diarrhea. The global prevalence of this disorder varies from 0.2 to 7.6%, depending on geographical regions and population characteristics.
Chronic symptom burden related to irritable bowel syndrome can substantially impair a person’s quality of life and affect daily activities and workplace productivity. Although the pathophysiology of this condition is not fully known, existing evidence suggests that visceral hypersensitivity, gut microbiota dysbiosis, impaired gut-brain axis, intestinal barrier dysfunction, low-grade inflammation, or neuroendocrine abnormalities can potentially trigger the development of irritable bowel syndrome.
The circadian system is the body’s internal clock that regulates 24-hour physical, mental, and behavioral changes in response to environmental day-night cycles. This complex phenomenon significantly impacts various physiological processes, including metabolism, hormone secretion, and immune response.
People working overnight or rotating shifts often experience metabolic disturbances due to a mismatch between their circadian rhythm and work schedule. Existing evidence indicates that shift work patterns can significantly increase the risk of diabetes, obesity, metabolic syndrome, hypertension, and cardiovascular disease.
Given the potential link between shift work and metabolic abnormalities, researchers at Jiaotong University, China, conducted a large-scale, prospective cohort study to investigate the association between night shift work and risk of irritable bowel syndrome among UK-based shift workers.
Study design
The researchers analyzed data from 266,605 participants in the UK Biobank, a large-scale database covering more than 500,000 participants from England, Scotland, and Wales. They specifically analyzed data on shift work patterns, the incidence of irritable bowel syndrome, and potential confounding factors, including sleep patterns, mental health, body mass index (a measure of overweight or obesity), and smoking and alcohol drinking habits.
Participants with a prior diagnosis of irritable bowel syndrome, coeliac disease, or gluten sensitivity were excluded to avoid reverse causality.
Key findings
The study analysis identified 5,218 new cases of irritable bowel syndrome in the database during a nine-year follow-up period.
The analysis, controlling for participants’ age and gender and potential confounding factors, revealed that participants who always work night shifts are at a higher risk of developing irritable bowel syndrome than those who never or rarely work night shifts. The observed increase in disease risk was more pronounced among participants with a body mass index of over 25 kilograms per meter square.
The risk of developing irritable bowel syndrome did not show significant differences between participants who sometimes or usually work on night shifts and those who never or rarely work on night shifts. Specifically, the fully adjusted hazard ratio for individuals who always worked night shift was 1.36, indicating a moderate but statistically significant increase in risk.
Study significance
The study reports that a permanent night shift work pattern can increase the risk of irritable bowel syndrome, especially in workers with a body mass index of over 25, which is considered overweight or obesity. The risk of disease remains high among workers who always work night shifts, irrespective of their age, gender, sleep duration, and mental health status.
Researchers have suggested certain mechanisms that may explain the observed association between night shift work patterns and the risk of irritable bowel syndrome. One possible mechanism is disruption of circadian rhythm due to an altered sleep-wake cycle, which in turn can trigger gut microbiota dysbiosis, impair gastrointestinal motility, increase secretion of pro-inflammatory mediators, and promote low-grade intestinal inflammation. All these changes can potentially contribute to the pathogenesis of irritable bowel syndrome.
Night shift work patterns are known to suppress the secretion of melatonin, a hormone required for sleep regulation and gastrointestinal protection. Although melatonin supplementation was not tested in this study, the authors note that previous research has shown it may help reduce symptoms and improve quality of life in patients with irritable bowel syndrome.
Shift workers' food habits and irregular eating patterns may also be potential risk factors for irritable bowel syndrome.
Notably, the current study reports that the effect of night shift work on disease risk is more pronounced among overweight or obese participants. This additional risk may come from obesity-related alterations in intestinal transit time, excessive consumption of ultra-processed foods, altered gut microbiota composition, and systemic low-grade inflammation. Lower levels of physical activity among obese or overweight participants may also be a contributing factor.
Because of the observational design, the study could not determine the causality of the observed associations. Moreover, the study analyzed data from UK Biobank participants primarily of European descent. This limitation may restrict the generalizability of the findings to other populations. Additional limitations include using self-reported sleep duration data and the inability to distinguish between subtypes of irritable bowel syndrome.
Overall, this large-scale, population-based study with a long-term follow-up period suggests that individuals diagnosed with irritable bowel syndrome or at higher risk of developing the disease may benefit from avoiding night shift work and maintaining a regular circadian rhythm.
However, further longitudinal and interventional studies are needed to confirm causality and explore underlying mechanisms.
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