Dear Editor:
We thank Gianfredi et al. for their generous comments regarding the methodology used in our recent umbrella review and welcome their clear discussion of common queries regarding the scope and methods of umbrella reviews. We believe their letter can serve as a valuable resource to guide the design, execution, and peer review of future umbrella reviews because it both informs the conduct of umbrella reviews and acts as a resource to inform researchers, reviewers, and readers of the scientific literature.
Umbrella reviews offer a powerful means for synthesizing a broad area of research in an efficient and readily accessible manner. Owing to the rapid pace of publication of both original research findings and systematic reviews, an overarching high-level synthesis of a field can provide the required insight into the current strength of the evidence across a wide range of settings, interventions, exposures, and outcomes. Our review, for example, was conducted in 1 y and was able to assess the strength of evidence for 38 chronic disease–related outcomes in relation to 1 important exposure (diet-associated inflammation)—a task that would be entirely unfeasible if we were to conduct a traditional systematic review and meta-analysis of the original data (1).
As with all research methods, there are some limitations related to umbrella reviews. As highlighted by Gianfredi et al., these include the reliance on the accuracy and rigor of previously published systematic reviews and meta-analyses. Also, umbrella reviews may not capture the strength of evidence of emerging areas not yet subjected to meta-analyses. Furthermore, because individual study effect estimates are not typically reanalyzed as part of umbrella reviews, this hinders the exploration of potential subgroup analyses. However, these limitations should not discourage the conduct of future umbrella reviews; rather, these limitations need to be acknowledged and discussed in the interpretation of their results.
Although the number of umbrella reviews in the published literature is growing, they remain relatively uncommon. For example, search results for “umbrella review” in the National Library of Medicine yielded ∼460 search results in 2021 at the time of writing this reply. By contrast, the term “systematic review” retrieved ∼39,000 results for the same period. Given the relatively novel method as well as the generally higher level of understanding and acceptability of traditional systematic review and meta-analysis methods, it is conceivable that reviewers may not be familiar with the expected scope of umbrella reviews. Gianfredi et al.’s efforts to clarify current misunderstandings should catalyze further acceptance of umbrella reviews as an important tool in advancing scientific knowledge.
Notes
The authors reported no funding received for this work.
Author disclosures: WM is currently funded by an Alfred Deakin Postdoctoral Research Fellowship and a Multiple Sclerosis Research Australia early-career fellowship. Wolfgang has previously received funding from the Cancer Council Queensland and university grants/fellowships from La Trobe University, Deakin University, University of Queensland, and Bond University, received industry funding and has attended events funded by Cobram Estate Pty. Ltd, received travel funding from Nutrition Society of Australia, received consultancy funding from Nutrition Research Australia, and has received speakers honoraria from The Cancer Council Queensland and the Princess Alexandra Research Foundation. MB is supported by a NHMRC Senior Principal Research Fellowship (1156072). MB has received Grant/Research Support from the NIH, Cooperative Research Centre, Simons Autism Foundation, Cancer Council of Victoria, Stanley Medical Research Foundation, Medical Benefits Fund, National Health and Medical Research Council, Medical Research Futures Fund, Beyond Blue, Rotary Health, A2 milk company, Meat and Livestock Board, Woolworths, Avant and the Harry Windsor Foundation, has been a speaker for Astra Zeneca, Lundbeck, Merck, Pfizer, and served as a consultant to Allergan, Astra Zeneca, Bioadvantex, Bionomics, Collaborative Medicinal Development, Lundbeck Merck, Pfizer and Servier – all unrelated to this work. SC is supported by a Deakin University Postgraduate Research (DUPR) Scholarship. HA is supported by Deakin University Postgraduate Industry Research Scholarship. AO is supported by a Future Leader Fellowship (#101160) from the Heart Foundation Australia and Wilson Foundation. She has received research funding from National Health & Medical Research Council, Australian Research Council, University of Melbourne, Deakin University, Sanofi, Meat and Livestock Australia and Woolworths Limited and Honoraria from Novartis. The Food & Mood Centre has received funding from the Fernwood Foundation, the A2 Milk Company and Be Fit Foods. AW is supported by an NHMRC Boosting Dementia Research Grant (GNT1171313). AW has received previous funding from the University of South Australia, the Nutrition Society of Australia and the Pork Cooperative Research Centre, all of which are unrelated to this work. FJ has received: (1) competitive Grant/Research support from the Brain and Behaviour Research Institute, the National Health and Medical Research Council (NHMRC), Australian Rotary Health, the Geelong Medical Research Foundation, the Ian Potter Foundation, The University of Melbourne; (2) industry support for research from Meat and Livestock Australia, Woolworths Limited, the A2 Milk Company, Be Fit Foods; (3) philanthropic support from the Fernwood Foundation, Wilson Foundation, the JTM Foundation, the Serp Hills Foundation, the Roberts Family Foundation, the Waterloo Foundation and; (4) travel support and speakers honoraria from Sanofi-Synthelabo, Janssen Cilag, Servier, Pfizer, Health Ed, Network Nutrition, Angelini Farmaceutica, Eli Lilly and Metagenics. Felice Jacka has written two books for commercial publication. ML is supported by a Deakin University Scholarship and has received research funding support from Be Fit Foods. LCB is supported by an NHMRC of Australia Emerging Leadership Investigator Grant (ID: 1172987) and a National Heart Foundation of Australia Post-Doctoral Research Fellowship (ID: 102498). LCB has received project funding from Edith Cowan University and Department of Health Western Australia, and travel support from the Nutrition Society of Australia and The University of Western Australia..
The authors’ responsibilities were as follows—WM: drafted the manuscript; and all authors: provided feedback to the manuscript and read and approved the final manuscript.
Contributor Information
Wolfgang Marx, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia.
Nicola Veronese, Aging Branch, Neuroscience Institute, National Research Council, Padova, Italy.
Jaimon Kelly, Centre of Applied Health Economics, Griffith University, Brisbane, Queensland, Australia; Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, Australia.
Sam Collins, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia.
Gina L Trakman, Department of Dietetics, Nutrition, and Sport, La Trobe University, Melbourne, Victoria, Australia.
Alexandra Wade, Alliance for Research in Exercise, Nutrition, and Activity, Allied Health and Human Performance, University of South Australia, Adelaide, South Australia, Australia.
Melissa Lane, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia.
Hajara Aslam, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia.
Adrienne O'Neil, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia; Melbourne School of Population & Global Health, University of Melbourne, Melbourne, Victoria, Australia.
James R Hebert, Department of Epidemiology and Biostatistics and Cancer Prevention and Control Program, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA; Department of Nutrition, Connecting Health Innovations LLC, Columbia, SC, USA.
Lauren Blekkenhorst, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia; Medical School, The University of Western Australia, Perth, Western Australia, Australia.
Michael Berk, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia.
Felice Jacka, From Deakin University, The Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine, Barwon Health, Geelong, Victoria, Australia; Black Dog Institute, Sydney, New South Wales, Australia; James Cook University, Townsville, Queensland, Australia; Centre for Adolescent Health, Murdoch Children's Research Institute, Melbourne, Victoria, Australia.
Reference
- 1. Marx W, Veronese N, Kelly JT, Smith L, Hockey M, Collins S, Trakman GL, Hoare E, Teasdale SB, Wade Aet al. The Dietary Inflammatory Index and human health: an umbrella review of meta-analyses of observational studies. Adv Nutr. 2021;12(5):1681–90. [DOI] [PMC free article] [PubMed] [Google Scholar]