Objectives: This study aims to evaluate the effect of coronavirus disease 2019 (COVID-19) on the long-term risk of digestive diseases in the general population. Design: Large-scale population-based cohort study based on a prospective cohort. Setting: UK Biobank cohort linked to multiple nationwide electronic health records databases. Participants: The cohort consisted of 112,311 individuals who survived the initial 30 days following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as well as two control groups: a contemporary group (n = 359,671) without any history of COVID-19, and a historical control group (n = 370,979) that predated the COVID-19 outbreak. Main outcome measures: Main outcomes were predefined digestive diseases. Hazard ratios and corresponding 95% confidence intervals (CI) were computed utilizing the Cox regression models after inverse probability weighting. Results: Compared with the contemporary control group, patients with previous COVID-19 infection had higher risks of digestive diseases, including functional gastrointestinal disorders (hazard ratios [HR] 1.95 (95% CI 1.62 to 2.35)); peptic ulcer disease (HR 1.27 (1.04 to 1.56)); gastroesophageal reflux disease (GERD) (HR 1.46 (1.34 to 1.58)); inflammatory bowel diseases (HR 1.40 (1.02 to 1.90)); gallbladder disease (HR 1.28 (1.13 to 1.46)); severe liver disease (HR 1.46 (1.12 to 1.90)); non-alcoholic liver disease (HR 1.33 (1.15 to 1.55)); and pancreatic disease (HR 1.43 (1.17 to 1.74)). The risks of GERD were stepwise increased with severity of the acute phase of COVID-19 infection. The results were consistent when using the historical cohort as the control group. Conclusions: Our study provides important insights into the association between COVID-19 and the long-term risk of digestive system disorders. COVID-19 patients are at a higher risk of developing gastrointestinal disorders, with stepwise increased risk with the severity and persisting even after one year follow-up.

Objectives: To prospectively investigate the associations of habitual fish oil use with Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, hospital admission, or mortality with Corona Virus Disease-19 (COVID-19) in a large-scale cohort. Design: Prospective population-based cohort study. Setting: UK Biobank. Participants: A total of 110 440 participants aged 37 -73 years who completed a questionnaire on supplement use, which included fish oil at baseline were enrolled between 2006 and 2010 and followed up until 2022. Main exposure: All participants filled out questionnaires about the habitual use of supplements, including fish oil. Main outcome measures: SARS-CoV-2 infection, COVID-19 hospital admission and COVID-19 mortality. Results: At baseline, 29 424 (26.6%) of the 110 440 participants reported habitual use of fish oil supplements. The multivariable adjusted hazard ratios for habitual users of fish oil versus non-users were 0.95 (0.93 to 0.98) for SARS-CoV-2 infection among participants with follow-up time less than 12.1 years but no significant associations were observed for participants with follow-up time more than 12.1 years. For COVID-19-related outcomes, the hazard ratios were 0.79 (95% confidence interval 0.71 to 0.88) for COVID-19 hospital admission and 0.72 (0.60 to 0.87) for COVID-19 mortality. For COVID-19-related outcomes, the association seemed to be stronger among those with longstanding illness. The Cox proportional hazard analysis after propensity-score matching yielded consistent results. Conclusions: Habitual fish oil supplement is associated with a lower risk of hospital admission and mortality with COVID-19, but not associated with SARS-CoV-2 infection in the population with more than 12.1 years of follow-up.