Ola Olén

Ola Olén is Adjunct Professor of Gastroenterology at the Division of Clinical Epidemiology, Department of Medicine Solna, Karolinska Institutet. He is also a senior consultant in paediatric gastroenterology at Sachs' Children and Youth Hospital, Stockholm.

Professor Olén leads a research group of approximately 15 researchers — from doctoral students to associate professors — focused on inflammatory bowel disease (IBD) pharmacoepidemiology, drug safety, and clinical outcomes. The group operates one of the world's most comprehensive population-based IBD research infrastructures (the COMPASS-IBD database), linking clinical, register, laboratory, pathology, and quality-register data for over 200, 000 IBD patients across Scandinavia, with additional international extensions through federated learning collaborations (Israel and Canada).

Olén is an Associate Editor of JCC Plus, a member of the ESPGHAN Paediatric IBD Porto Group, and a co-author of multiple European (ECCO, ESPGHAN) and Swedish IBD treatment guidelines.

KEY METRICS, spring 2026

SELECTED RESEARCH HIGHLIGHTS

• Landmark Scandinavian population-based studies of colorectal cancer risk in ulcerative colitis (Lancet, 2020) and Crohn's disease (Lancet Gastroenterol Hepatol, 2020) and of rectal cancer risk in ulcerative proctitis (Gastroenterology 2026)
• Global IBD epidemiology across epidemiologic stages (Nature, 2025)
• Increased malignancy and mortality in childhood-onset IBD (BMJ 2017, Gastroenterology, 2019) and adult-onset IBD (Gut, 2020)
• Lymphoma risk trends in IBD (Clin Gastroenterol Hepatol, 2023)
• Serious infection risk across IBD therapies stratified by age (J Crohns Colitis, 2026)
• Cancer incidence across advanced therapies in ulcerative colitis (J Crohns Colitis, 2025)
• Cardiovascular outcomes, published in several high ranking journals 2024-2026
• Pioneering federated learning for IBD pharmacoepidemiology across four countries
• Pivotal clinical trials in cognitive behavioural therapy for treatment of IBS and FAP for children (American Journal of Gastroenterology 2017, Clinical Gastroenterology and Hepatology 2019)
• The first study on adoloescent risk factors for presence and persistence of adult IBS (Gastroenterology 2026) and an important study of the bidirectional gut-brain interactions in adolescent IBS (Clinical Gastroenterology and Hepatology 2024)

Our research focuses on the questions that patients and clinicians actually want answered - and that could change clinical care

IBD pharmacoepidemiology and safety

Our core research programme addresses a fundamental clinical challenge: how to make IBD treatment decisions safer for individual patients. The therapeutic armamentarium in IBD has expanded dramatically in recent years, with new advanced drugs - anti-TNF agents, vedolizumab, ustekinumab, JAK inhibitors, IL-23 inhibitors, and sphingosine-1-receptor modulators - being added almost annually. As a result, a growing proportion of the IBD population is exposed to potent immunosuppression over extended periods, and the patients treated today are often more refractory and comorbid than participants in the pivotal trials of these drugs. Yet current evidence on medication safety rests largely on average risks from selected trial populations, leaving clinicians without guidance for patients who differ by age, comorbidity, inflammatory burden, or treatment history.

To address this, we have built and continuously maintain a population-based IBD research infrastructure that is unmatched in scope and depth, the COMPASS-IBD database (Cohortfor Outcomes, Medication Safety, and Precision Assessment in IBD):

• Swedish nationwide IBD cohort: All individuals with an IBD diagnosis in the Swedish National Patient Register since 1964 (~125, 000 patients), each matched with up to 10 general-population comparators and linked to national patient, prescribed drug, cancer, cause of death, pathology, and quality registers (SWIBREG), as well as laboratory data, socioeconomic data, and histopathology data.
• Merged Scandinavian dataset: An equivalent Danish cohort, physically merged with the Swedish data at Statistics Denmark, creating a combined dataset of over 200, 000 IBD patients with matched controls — accessible via remote access for researchers in both countries.
• Federated learning consortium: Through the Rhino Federated Computing platform, we perform joint analyses with collaborators abroad without sharing individual-level data, enabling studies of rare outcomes, newer medications, and smaller subgroups that no single national dataset can power.

Our main research lines include:

• Cancer risk across IBD medications and clinically relevant subgroups of patients
• Cardiovascular disease, venous thromboembolism, and serious infections in treated IBD
• Quantification of acute and cumulative inflammatory burden
• Comparative real-world effectiveness and safety of newer advanced therapies — including head-to-head comparisons
• Paediatric IBD outcomes, including surgery, growth, education, and fertility
• Mortality and prognosis across the lifespan in IBD

Our findings have contributed directly to international guideline recommendations (ECCO, ESPGHAN) and are published in journals including the Lancet, Nature, BMJ, Gastroenterology, and Gut.

Disorders of gut–brain interaction

A secondary research line addresses disorders of gut–brain interaction (DGBI), primarily irritable bowel syndrome (IBS) and functional abdominal pain in children and adolescents. In a series of randomised clinical trials, we have demonstrated the effectiveness of internet-delivered cognitive behavioural therapy for young people with IBS, increasing access to evidence-based psychological treatments. We also study risk factors for DGBI in birth cohorts and national registers. Olén currently contributes to a new Swedish national care programme for DGBI in children.

Collaboration and comissioned research

Our group has extensive experience with post-authorisation safety studies (PASS) and regulatory observational research commissioned by pharmaceutical companies, as well as academically driven collaborative projects with industry partners.

The combination of a validated, continuously updated total-population-based data infrastructure (The COMPASS-IBD database), published and validated exposure and outcome algorithms, deep domain expertise in IBD pharmacoepidemiology, and a well-established international collaborative network makes us well positioned to deliver high-quality observational safety and effectiveness studies — from study design through regulatory-grade reporting.

We welcome enquiries regarding:

• Academic collaborative research projects
• Commissioned post-authorisation safety studies (PASS)
• Real-world evidence studies on treatment effectiveness and safety
• Exploratory analyses supporting drug development programmes in IBD

Olén is regularly engaged as a lecturer in inflammatory bowel disease, disorders of gut–brain interaction, and epidemiology with >20 lectures annually. He served as director of studies for the Research School in Epidemiology for Clinicians at Karolinska Institutet (2009–2013) and for the Clinical Research School at the Department of Clinical Science and Education (2014–2015), and was director of the national course in paediatric gastroenterology, hepatology, and nutrition funded by the National Board of Health and Welfare (2012–2017).

Supervision record:

• 12 doctoral students
• 8 postdoctoral researchers (main supervisor)

Former doctoral students: Bonnert M, Uusijärvi A, Lalouni M, Granlund J, Schollin-Ask L, Forss A, Mouratidou N, Mahmood M, Thulin H, Jossan N, Sjölund J.

Current doctoral students: Voghera S, Kristjansson K, Oest P, Andersson F.

Former postdoctoral researchers: Arnell H, Malmborg P, Everhov ÅH, Eriksson C, Forss A

Current postdoctoral researchers: Bröms G, Rolandsdotter H, Soini T.

For potential collaborators and team-members

We are an active and growing research group with a strong commitment to mentoring at all career stages. Our research environment offers:

• Access to one of the world's most comprehensive population-based IBD datasets
• An established international collaborative network
• Hands-on supervision in pharmacoepidemiology, register-based research, biostatistics, and clinical informatics
• A multidisciplinary team combining clinical gastroenterology, epidemiology, biostatistics, and data science
• Regular opportunities to present at major international conferences (ECCO, ESPGHAN, DDW, UEGW)