Current Organizations / Institutes

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Previous Organizations / Institutes

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Reidar Fossmark has a total of 242 co-authors. Here are the top co-authors by number of shared publications:

  • Helge Lyder Waldum

    Department of Medicine and Health, Norwegian University of Science and Technology, Trondheim, Norway

    51 shared publications
  • Gunnar Qvigstad

    Department of Clinical and Molecular Medicine, NTNU, Norwegian University of Science and Technology, Trondheim, Norway

    10 shared publications
  • Unni Syversen

    Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway

    8 shared publications
  • Øyvind Hauso

    Department of Clinical and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway

    8 shared publications
  • Astrid Kamilla Stunes

    Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology (NTNU), Norway

    7 shared publications
  • Arne K. Sandvik

    Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway

    6 shared publications

Latest Publications

  • Open Access

    Telomere Length in Celiac Disease in a Population-Based Cohort: A HUNT Study

    by Reidar Fossmark, Henrik Hjorth-Hansen, Lisa Lirussi, Torben Lüders, Martina Visnovska, Yan Liu, Øyvind Salvesen, Hilde Loge Nilsen, Eivind Ness-Jensen

    INTRODUCTION: Celiac disease (CeD) occurs in genetically predisposed individuals who are exposed to dietary gluten proteins. Genome-wide association studies have found CeD to be associated with a genetic predisposition to shorter telomere length. It was therefore of interest to measure leukocyte telomere length in a large cohort of patients with CeD. METHODS: This study was population-based and included a defined cohort of patients with CeD in the Trøndelag Health Study. Leukocyte telomere length was measured by quantitative polymerase chain reaction (PCR) in patients and controls 1:2 matched for age, sex, alcohol, and tobacco use. RESULTS: The study population consisted of 58.7% women, with mean age 43 (SD 14.5) years, where half were never smokers, and the majority consumed little or no alcohol. Telomer length in 1,077 patients with CeD did not differ significantly from 2,147 matched controls, 10.39 kb (SD 2.21) vs 10.52 kb (SD 2.25), P = 0.088. In a mixed linear model, we found higher age and alcohol consumption, but not tobacco use or sex, to be associated with shorter telomere length. The telomere length did not differ between patients with newly diagnosed and known CeD. DISCUSSION: This large population-based study provides evidence that CeD is not associated with clinically meaningful telomere shortening.

  • Open Access

    The Use of Proton Pump Inhibitors Among Adults in Norway—A Nationwide Drug Utilization Study

    by Reidar Fossmark, Sveinung Molnes, Liv Sagatun, Øyvind Salvesen, Olav Spigset

    The use of proton pump inhibitors (PPIs) has increased in Western countries over several decades, and there is concern about unsubstantiated indications and effects of long‐term use. The study aimed to describe the prevalence, incidence, indications, and prescription pattern for PPIs over the past decade in an entire national cohort. This nationwide drug utilization study used data from the Norwegian Prescription Database and Norwegian Patient Registry. Patterns of PPI use were investigated from 2009 to 2022. Prevalent, long‐term, and incident PPI use were calculated. The indication for PPI was defined by the diagnosis code linked to each prescription. Upper endoscopies during the study period were assessed for incident PPI users. PPI prescription increased from 58.1 mill DDD in 2009 to 166.9 mill DDD in 2022, that is, 43 and 106 DDD/1000 inhabitants/day. Prevalent PPI use increased from 3.5% to 9.9%, paralleling an increased incidence from 2.9% to 5.4%. The dominant indications in 2009 and 2022 were esophageal disease in primary care (72.5% and 57.6% of total DDDs) and GERD in specialist care (10.7% and 4.7% of total DDDs). Musculoskeletal disorders, pain, and ulcer prophylaxis all increased during the period. Upper endoscopy around incident PPI use decreased from 25.3% to 11.1%. In conclusion, the 2.46‐fold increase in prevalent PPI use was caused by an absolute increase in PPI prescribed against esophageal disease and GERD, and prophylaxis in patients using ulcerogenic comedication, mainly prescribed in primary care. The findings may help inform strategies to reduce a probable overuse of PPIs.


  • Eradication of Helicobacter pylori by a potassium-competitive acid blocker alone?

    by Helge Waldum, Reidar Fossmark

    Helicobacter pylori (H. pylori), the dominating cause of gastric cancer, most often infects children initiating inflammation in the antral part and spreads orally to the oxyntic mucosa. Traditionally, eradication of H. pylori has been based upon a combination of antibiotics together with a proton pump inhibitor (PPI) to reduce gastric destruction of the antibiotics. Recently it has been shown that the more efficient inhibitors of acid secretion, the potassium-competitive acid blockers (PCABs) in combination with amoxicillin alone gave highly sufficient H. pylori eradication. To further elucidate the importance of gastric acidity we studied the literature for the connection between gastric acidity and the presence of H. pylori. It is well-known that H. pylori is dependent of some acidity in the surroundings to neutralize NH3 produced by its urease, explaining the loss of H. pylori in total oxyntic atrophy. With adequate dosing PCABs can induce almost complete anacidity for 24-h which probably is necessary for H. pylori eradication. Even a short period with hypergastrinemia may induce mutations in the target cell of gastrin, the enterochromaffin-like (ECL) cell which may contribute to the relatively short interval between H. pylori eradication and gastric cancer in the users of profound acid inhibitors. The use of PCABs alone dosed sufficiently seems promising for H. pylori eradication, but a combination with a gastrin antagonist would be preferable.


  • Open Access

    Esophageal cancers missed at upper endoscopy in Central Norway 2004 to 2021 – A population-based study

    by Synne Straum, Karoline Wollan, Lars Cato Rekstad, Reidar Fossmark

    Introduction: The incidence of esophageal cancers is increasing in many Western countries and the rate of missed esophageal cancers (MEC) at upper endoscopy is of concern. We aimed to calculate the MEC rate and identify factors associated with MEC. Methods: This was a retrospective population-based cohort study including 613 patients diagnosed with esophageal cancer in Central Norway 2004–2021. MEC was defined as esophageal cancer diagnosed 6–36 months after a non-diagnostic upper endoscopy. Patient characteristics, tumor localization, histological type and cTNM stage were recorded. Symptoms, endoscopic findings, use of sedation and endoscopists experience at the endoscopy prior to esophageal cancer diagnosis and at the time of diagnosis were recorded. The association between these factors and MEC was assessed. Results: Forty-nine (8.0%) of 613 cancers were MEC. There was a significant increase in annual numbers of esophageal cancer (p < 0.001) as well as of MEC (p = 0.009), but MEC rate did not change significantly (p = 0.382). The median time from prior upper endoscopy to MEC diagnosis was 22.9 (12.1–28.6) months. MEC patients were older and were diagnosed with disease with a lower cTNM stage and cT category than non-missed cancers, whereas tumor localization and histological type were similar between the groups. The use of sedation or endoscopist experience did not differ between the endoscopy prior to esophageal cancer diagnosis and at the time of diagnosis. High proportions of MEC patients had Barrett’s esophagus (n = 25, 51.0%), hiatus hernia (n = 26, 53.1%), esophagitis (n = 10, 20.4%) or ulceration (n = 4, 8.2%). Significant proportions of MECs were diagnosed after inappropriate follow-up of endoscopic Barrett’s esophagus, histological dysplasia or ulcerations. Conclusions: The annual number of MEC increased during the study period, while the MEC rate remained unchanged. Endoscopic findings related to gastroesophageal reflux disease such as esophagitis and Barrett’s esophagus were identified in a high proportion of patients with subsequent MECs. Cautious follow-up of these patients could potentially reduce MEC-rate.


  • Open Access

    Changes in the Gastrointestinal Microbiota Induced by Proton Pump Inhibitors—A Review of Findings from Experimental Trials

    by Reidar Fossmark, Maya Olaisen

    The use of proton pump inhibitors (PPIs) has increased considerably in many Western countries, and there is concern that numerous conditions and diseases associated with PPI use may be adverse events. The main function of gastric acid is to defend the organism against orally ingested microorganisms, and there is also concern that alterations not only in the gastric microbiome but also the downstream intestinal microbiome may increase the risk of disease or alter the course of preexisting disease. The current study is a systematic review of the available evidence from experimental trials investigating the effects of PPIs on the gastrointestinal microbiota by next-generation sequencing. Thirteen studies were identified. The effects of PPIs were seen on alterations in diversity and richness in some of the studies, while a larger proportion of the studies detected alterations at various taxonomic levels. The general finding was that PPI use caused an increase in bacteria normally found in the oral microbiota in both the upper and lower GI tract. The most consistent taxonomic alterations seemed to be increases in oral flora along the axis Streptococcaceae and Streptococcus at genus level and various Streptococcus spp., as well as Veillonellaceae, Veillonella and Haemophilus.


  • Open Access

    Epstein–Barr Virus and Clinico-Endoscopic Characteristics of Gastric Remnant Cancers Compared to Proximal Non-Remnant Cancers: A Population-Based Study

    by Erling A. Bringeland, Christina Våge, Ann A. S. Ubøe, Alina D. Sandø, Patricia Mjønes, Reidar Fossmark

    Epstein–Barr virus (EBV) is associated with 5–10% of gastric cancers and is recognized as a distinct molecular subtype. EBV positivity is particularly high in gastric remnant cancer (GRC), which may inform the mode of clinical presentation and findings at endoscopy. Most data are from the East, and the question remains how this applies to a Western cohort. We conducted a population-based study in Central Norway, 2001–2016. Patients with GRC (n = 78) and patients with non-GRC proximally located cancer and available tissue for EBV status (n = 116, control group) were identified from the Norwegian Cancer Registry. Relevant data were collected from the individual patient journals. EBV status was assessed using in situ hybridization. The median latency time from the distal gastrectomy to GRC was 37.6 (range 15.7–68.0) years. GRC more often presented with GI bleeding, 31.0% vs. 16.1%, p = 0.017, and at endoscopy more seldom with an ulcer, 19.7% vs. 38.2%, p = 0.012, or a tumour, 40.8% vs. 66.4%, p < 0.001. For GRC, 18.7% were EBV-positive compared to 6.0% among the controls, p = 0.006. EBV status was not associated with patient age, sex, or Lauren histological type. No difference in long-term survival rates between GRC and controls was found or between EBV-positive vs. -negative GRCs. In conclusion, a higher proportion of GRC cases, compared to controls, are EBV positive, indicating different causative factors. The mode of clinical presentation and findings at endoscopy were more subtle in the patients with GRC.


  • Open Access

    Early Gastric Cancers in Central Norway 2001 to 2016—A Population-Based Study

    by Camilla J. Kvamme, Thomas L. Stillingen, Alina D. Sandø, Patricia Mjønes, Erling A. Bringeland, Reidar Fossmark

    Early gastric cancers (EGCs) are confined to the gastric mucosa and submucosa irrespective of lymph node metastases and constitute only a minor proportion of gastric cancer in Western countries. We aimed to characterize EGCs and assess the survival of EGC in Central Norway during 2001–2016. A retrospective population-based study on 1205 patients with gastric cancer was performed. At the time, surgical resection was the standard treatment, and 88 (7.3%) EGCs were identified. Histopathological specimens were re-examined, and the eCura score and survival were evaluated. The number of gastric cancers declined (p = 0.010), but the relative proportion of EGC was unchanged during the study period. EGCs were more often of the Lauren intestinal type (p < 0.001) compared with controls. A significant proportion (9.4%, n = 5) of the patients with a low-risk eCura had lymph node metastases, whereas further exclusion of tumors with histological ulceration or SM2 invasion identified an N0 cohort. The median survival for EGC patients was 117.1 months (95% CI 99.8–134.3) and the 5-year overall survival was 75%. Twelve deaths were cancer-related, either due to postoperative complications (5.7%, n = 5) or cancer recurrence (8%, n = 7). In conclusion, EGCs constituted a minor but constant proportion of gastric cancers. eCura alone was insufficient in predicting patients with pN0 disease.


  • Open Access

    Gastric remnant cancer and long-term survival in Central Norway 2001 to 2016 – A population-based study

    by Ann Amelia Savage Ubøe, Christina Våge, Patricia Mjønes, Erling A. Bringeland, Reidar Fossmark


  • Open Access

    The impact of proton pump inhibitors on the course of ulcerative colitis: a cohort study of over 10,000 newly diagnosed patients in Norway

    by Reidar Fossmark, Sandre Svatun Lirhus, Marte Lie Høivik

    Proton pump inhibitors (PPI) affect the gastrointestinal microbiota, which is thought to play a role in the pathogenesis of ulcerative colitis (UC). Previous studies suggest an association between PPI use and risk of incident UC as well as disease course. The aim of the study was to examine if PPI exposure is associated with disease course in UC patients. A national cohort consisting of all newly diagnosed UC patients from 2010 to 2020 was defined combining data from Norwegian registries. PPI exposure was included as a time dependent variable with a 30 day time lag from starting the drug. Outcomes were starting advanced therapies including anti-TNF, systemic glucocorticoids, any additional systemic anti-inflammatory medication and undergoing colectomy during follow-up. Time-dependent Cox regressions included the variables PPI use, first systemic glucocorticoid prescription, first UC hospitalization, age-groups and sex. The study cohort consisted of 10,149 patients with median age 40 years (IQR 27-56) and 56% males. PPI use independently increased the risk of starting advanced therapies (HR 1.54, 95% CI 1.36-1.73, p < 0.005), starting systemic glucocorticoids (HR 1.20, 95% CI 1.07-1.34, p < 0.005), starting any additional anti-inflammatory treatment (HR 1.18, 95%CI 1.05-1.32, p < 0.01) and undergoing colectomy (HR 1.52, 95%CI 1.17-1.98, p < 0.005). PPI use was associated with unfavorable outcomes including advanced therapy initiation, additional anti-inflammatory medications and undergoing colectomy. Although further studies are needed, the evidence suggests that PPIs could affect the course of UC and should be used cautiously in UC patients.


  • Open Access

    Is empiric proton pump inhibition in patients with symptoms of extraesophageal gastroesophageal reflux justified?

    by Reidar Fossmark, Eivind Ness-Jensen, Øystein Sørdal

    Background: The prevalence of gastroesophageal reflux disease (GERD) has had a marked increase in Western countries with a paralleling interest in extraesophageal (EE) manifestations of GERD, including laryngopharyngeal reflux (LPR). There are considerable differences in clinical practice between gastroenterologists, otolaryngologists and pulmonologists. Methods: In this narrative review we address some of these controversies concerning EE manifestations of GERD and LPR. Results: It is disputed whether there is causal relationship between reflux and the numerous symptoms and conditions suggested to be EE manifestations of GERD. Similarly, the pathophysiology is uncertain and there are disagreements concerning diagnostic criteria. Consequently, it is challenging to provide evidence-based treatment recommendations. A significant number of patients are given a trial course with a proton pump inhibitor (PPI) for several months before symptoms are evaluated. In randomized controlled trials (RCTs) and meta-analyses of RCTs PPI treatment does not seem to be advantageous over placebo, and the evidence supporting that patients without verified GERD have any benefit of PPI treatment is negligible. There is a large increase in both over the counter and prescribed PPI use in several countries and a significant proportion of this use is without any symptomatic benefit for the patients. Whereas short-term treatment has few side effects, there is concern about side-effects after long-term use. Although empiric PPI treatment for suspected EE manifestations of GERD instead of prior esophageal 24-hour pH and impedance monitoring is included in several guidelines by various societies, this practice contributes to overtreatment with PPI. Conclusion: We argue that the current knowledge suggests that diagnostic testing with pH and impedance monitoring rather than empiric PPI treatment should be chosen in a higher proportion of patients presenting with symptoms possibly attributable to EE reflux.