title: Stable isotope and high precision concentration measurements confirm that all humans produce and exhale methane.
abstract: Mammalian formation of methane (methanogenesis) is widely considered to occur exclusively by anaerobic microbial activity in the gastrointestinal tract. Approximately one third of humans, depending on colonization of the gut by methanogenic archaea, are considered methane producers based on the classification terminology of high and low emitters. In this study laser absorption spectroscopy was used to precisely measure concentrations and stable carbon isotope signatures of exhaled methane in breath samples from 112 volunteers with an age range from 1 to 80 years. Here we provide analytical evidence that volunteers exhaled methane levels were significantly above background (inhaled) air. Furthermore, stable carbon isotope values of the exhaled methane unambiguously confirmed that this gas was produced by all of the human subjects studied. Based on the emission and stable carbon isotope patterns of various age groups we hypothesize that next to microbial sources in the gastrointestinal tracts there might be other, as yet unidentified, processes involved in methane formation supporting the idea that humans might also produce methane endogenously in cells. Finally we suggest that stable isotope measurements of volatile organic compounds such as methane might become a useful tool in future medical research diagnostic programs.
authors.affiliation: Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany. Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany. Heidelberg Center for the Environment (HCE), Ruprecht Karls University Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Keppler
authors.forename: Amanda
authors.initials: A
authors.lastname: Schiller
authors.forename: Robert
authors.initials: R
authors.lastname: Ehehalt
authors.forename: Markus
authors.initials: M
authors.lastname: Greule
authors.forename: Jan
authors.initials: J
authors.lastname: Hartmann
authors.forename: Daniela
authors.initials: D
authors.lastname: Polag
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001944:Breath Tests; D002247:Carbon Isotopes / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008697:Methane / Q000378:metabolism*; D008875:Middle Aged; D055815:Young Adult
chemical_list: D002247:Carbon Isotopes; D008697:Methane