A large study has found that people exposed to higher levels of outdoor artificial light at night may have a lower chance of developing inflammatory bowel disease (IBD), a long-term condition that causes inflammation in the digestive system. The findings, drawn from population data, also suggest that people with IBD who lived in brighter night-time areas needed fewer hospital stays and outpatient appointments. Researchers say the results may help explain some of the environmental factors linked to IBD, although more work is needed before firm conclusions can be drawn.
Why researchers looked at night-time light
Previous research has shown that people living in cities tend to have a higher risk of developing IBD than those in rural areas. Scientists have been trying to understand why. One theory is that exposure to artificial light after dark could affect the body’s internal clock, hormone levels, and the balance of bacteria that live in the gut, all of which have been linked to inflammation. To explore this further, a team of researchers examined whether the amount of outdoor artificial light people were exposed to at night was connected to their chances of developing IBD, and to how their condition was managed afterwards.
What the researchers did
The team grouped areas into three categories based on how much artificial light was detected outdoors at night: low, medium, and high. They then looked at data from more than 3.9 million people born in urban areas over several decades, tracking who went on to develop IBD. Separately, they compared over 32,000 people diagnosed with IBD against more than 160,000 people without the condition, matched for similar characteristics. A further analysis looked at how often people with IBD needed hospital care or outpatient visits in the year after diagnosis, depending on their night-time light exposure.
What the study found
In the group followed from birth, the amount of artificial light present at the time of birth did not appear to make a meaningful difference to the chances of developing IBD later in life, whether exposure was medium or high.
In the second analysis, which compared adults with and without IBD, the picture was different. People exposed to high levels of outdoor artificial light at night were found to have a noticeably lower likelihood of developing IBD as adults compared with those exposed to low levels. This pattern held true for both of the main types of IBD, Crohn’s disease and ulcerative colitis.
Among people already diagnosed with IBD, those living with higher night-time light exposure had somewhat fewer IBD-related outpatient appointments and fewer hospital admissions in the year following diagnosis. However, night-time light exposure did not appear to affect the likelihood of needing surgery or visiting an emergency department.
Why this matters
These findings add to a growing picture of how the environment where people live may play a role in IBD, alongside genetics and other known risk factors. The researchers noted that understanding environmental influences on IBD, and on how severe the condition becomes, could eventually help inform prevention strategies. However, they stressed this research does not show that artificial light directly causes or prevents IBD, only that a link exists.
What to keep in mind
- The study measured outdoor light only, not exposure to indoor lighting or screens, which could also play a role.
- Light levels were not adjusted for seasonal changes throughout the year.
- The rise of energy-efficient LED lighting may make older light measurements less accurate over time.
- Some personal and clinical details were not available in the records used.
- The results show a pattern, not proof that artificial light changes a person’s risk of IBD.
Further research will be needed to understand whether night-time light exposure has any direct biological effect, or whether it reflects other lifestyle or environmental factors common in brightly lit areas.
Reference
Kuenzig ME, Bernstein CN, Coward S, et al. The association between artificial light at night and inflammatory bowel disease incidence, surgery, and health services utilization: population-based observational studies. Inflamm Bowel Dis. Published online 17 July 2026. doi:10.1093/ibd/izag141
This article is a journalistic summary for informational purposes only. It does not constitute clinical advice or a recommendation to alter treatment decisions.