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Tavlo M, Skakkebæk NE, Mathiesen ER, Kristensen DM, Kjær KH, Andersson AM, Lindahl-Jacobsen R. Hypothesis: Metformin is a potential reproductive toxicant. Front Endocrinol (Lausanne) 2022; 13:1000872. [PMID: 36339411 PMCID: PMC9627511 DOI: 10.3389/fendo.2022.1000872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 10/05/2022] [Indexed: 11/25/2022] Open
Abstract
Metformin is the first-line oral treatment for type 2 diabetes mellitus and is prescribed to more than 150 million people worldwide. Metformin's effect as a glucose-lowering drug is well documented but the precise mechanism of action is unknown. A recent finding of an association between paternal metformin treatment and increased numbers of genital birth defects in sons and a tendency towards a skewed secondary sex ratio with less male offspring prompted us to focus on other evidence of reproductive side effects of this drug. Metformin in humans is documented to reduce the circulating level of testosterone in both men and women. In experimental animal models, metformin exposure in utero induced sex-specific reproductive changes in adult rat male offspring with reduced fertility manifested as a 30% decrease in litter size and metformin exposure to fish, induced intersex documented in testicular tissue. Metformin is excreted unchanged into urine and feces and is present in wastewater and even in the effluent of wastewater treatment plants from where it spreads to rivers, lakes, and drinking water. It is documented to be present in numerous freshwater samples throughout the world - and even in drinking water. We here present the hypothesis that metformin needs to be considered a potential reproductive toxicant for humans, and probably also for wildlife. There is an urgent need for studies exploring the association between metformin exposure and reproductive outcomes in humans, experimental animals, and aquatic wildlife.
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Affiliation(s)
- Maja Tavlo
- Faculty of Health Sciences, Department of Epidemiology, Biostatistics, and Biodemography, University of Southern Denmark, Odense C, Denmark
- Interdisciplinary Center on Population Dynamics, University of Southern Denmark, Odense C, Denmark
- *Correspondence: Maja Tavlo,
| | - Niels E. Skakkebæk
- Department of Growth and Reproduction, Copenhagen University Hospital — Rigshospitalet, Copenhagen, Denmark
- International Center for Research and Research Training in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Elisabeth R. Mathiesen
- Centre for Pregnant Women with Diabetes, Department of Endocrinology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
- Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - David M. Kristensen
- Department of Neurology, Danish Headache Center, Rigshospitalet - Glostrup, University of Copenhagen, Copenhagen, Denmark
- University of Rennes, Inserm, École des hautes études en santé publique (EHESP), Irset (Institut de recherche en santé environment et travail) UMR_S, Rennes, France
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Kurt H. Kjær
- Globe Institute, Section for GeoGenetics, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Anna-Maria Andersson
- Department of Growth and Reproduction, Copenhagen University Hospital — Rigshospitalet, Copenhagen, Denmark
- International Center for Research and Research Training in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Rune Lindahl-Jacobsen
- Faculty of Health Sciences, Department of Epidemiology, Biostatistics, and Biodemography, University of Southern Denmark, Odense C, Denmark
- Interdisciplinary Center on Population Dynamics, University of Southern Denmark, Odense C, Denmark
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