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Body mass index and risk of infections: a Mendelian randomization study of 101,447 individuals

European Journal of Epidemiology volume 35, pages 347–354 (2020)Cite this article

Abstract

Body mass index (BMI) has been related to risk of infections. The aim of this study was to assess the shape of the association between BMI and risk of infections and to evaluate whether such associations represent causality. We included 101,447 individuals from The Copenhagen General Population Study who had BMI measured. Outcome was hospital contacts related to infections. The shape of the association between BMI and risk of infections was examined using restricted cubic spline Cox regression. To evaluate causality, we used Mendelian randomization, an epidemiological method that counteracts confounding and reverse causality by using genetic variation as instrumental variables. We created a genetic risk score based on five genetic variants causing lifelong higher BMI and used this score in instrumental variable analysis. During median follow-up of 8.8 years, 10,263 hospital contacts related to infections were recorded. We found a U-shaped association between BMI and risk of any infection and pneumonia, and a linear association between BMI and risk of skin infection, urinary tract infection, and sepsis. In instrumental variable analyses, higher BMI was associated with increased risk of skin infection: odds ratio 1.12 (95% CI 1.03–1.22) for a genetically induced 1 unit increase in BMI. Observationally, low as well as high BMI was associated with increased risk of any infection and pneumonia, whereas only high BMI was associated with increased risk of skin infection, urinary tract infection, and sepsis. High BMI was causally associated with increased risk of skin infection.

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Funding

This work was supported by the Novo Nordisk Foundation [NNF15OC0017740] and the Danish Council for Independent Research | Medical Sciences [DFF – 6110-00075]. The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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Authors and Affiliations

  1. Center for Clinical Research and Prevention, Bispebjerg and Frederiksberg Hospital, The Capital Region, Nordre Fasanvej 57, 2000, Frederiksberg, Denmark

    Matilde Winter-Jensen, Tine Jess & Kristine H. Allin

  2. Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Copenhagen, Denmark

    Shoaib Afzal

  3. The Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Copenhagen, Denmark

    Shoaib Afzal & Børge G. Nordestgaard

  4. Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark

    Tine Jess

  5. Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

    Børge G. Nordestgaard

  6. Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

    Kristine H. Allin

Authors
  1. Matilde Winter-Jensen
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  2. Shoaib Afzal
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Correspondence to Kristine H. Allin.

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Winter-Jensen, M., Afzal, S., Jess, T. et al. Body mass index and risk of infections: a Mendelian randomization study of 101,447 individuals. Eur J Epidemiol 35, 347–354 (2020). https://doi.org/10.1007/s10654-020-00630-7

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  • DOI: https://doi.org/10.1007/s10654-020-00630-7

Keywords

  • Body mass index
  • Causality
  • Infections
  • Mendelian randomization analysis
  • Obesity
  • Overweight