Gastrointestinal issues are the most commonly reported health problem among female nurses, a recently published analysis of more than 20,000 female healthcare workers shows.

Researchers conducting the Korea Nurses’ Health Study surveyed more than 13% of the country’s female nursing workforce in order to determine how occupational factors impact their chronic disease risks and reproductive health. The study’s authors include researchers from Seoul National University, Brigham and Women’s Hospital, Harvard University and Brown University.

The results, published online in the Journal of Women’s Health, found that gastrointestinal problems such as ulcers and reflux esophagitis were the most commonly cited health issue among the nurses, reported by nearly 26% of those surveyed. Allergies and eczema were also common, reported by 19.5% and 11.6% of the nurses, respectively.

The study also found that more than 88% of the survey respondents had worked night shifts, a higher percentage than those reported by nursing studies in the United States. That’s likely due to the way nursing shifts are structured in Korea, researchers said, since nurses typically rotate through working day, evening and night shifts.

Future results of the study, which is ongoing, should “provide a valuable opportunity to identify associations between lifestyle and environmental factors and risk factors for the development of chronic diseases,” Journal of Women’s Health editor Susan G. Kornstein, M.D., said Thursday in a statement on the findings.