title: The effects of sex hormones on immune function: a meta-analysis.
abstract: The effects of sex hormones on immune function have received much attention, especially following the proposal of the immunocompetence handicap hypothesis. Many studies, both experimental and correlational, have been conducted to test the relationship between immune function and the sex hormones testosterone in males and oestrogen in females. However, the results are mixed. We conducted four cross-species meta-analyses to investigate the relationship between sex hormones and immune function: (i) the effect of testosterone manipulation on immune function in males, (ii) the correlation between circulating testosterone level and immune function in males, (iii) the effect of oestrogen manipulation on immune function in females, and (iv) the correlation between circulating oestrogen level and immune function in females. The results from the experimental studies showed that testosterone had a medium-sized immunosuppressive effect on immune function. The effect of oestrogen, on the other hand, depended on the immune measure used. Oestrogen suppressed cell-mediated immune function while reducing parasite loads. The overall correlation (meta-analytic relationship) between circulating sex hormone level and immune function was not statistically significant for either testosterone or oestrogen despite the power of meta-analysis. These results suggest that correlational studies have limited value for testing the effects of sex hormones on immune function. We found little evidence of publication bias in the four data sets using indirect tests. There was a weak and positive relationship between year of publication and effect size for experimental studies of testosterone that became non-significant after we controlled for castration and immune measure, suggesting that the temporal trend was due to changes in these moderators over time. Graphical analyses suggest that the temporal trend was due to an increased use of cytokine measures across time. We found substantial heterogeneity in effect sizes, except in correlational studies of testosterone, even after we accounted for the relevant random and fixed factors. In conclusion, our results provide good evidence that testosterone suppresses immune function and that the effect of oestrogen varies depending on the immune measure used.
authors.affiliation: ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia.|Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia.
authors.forename: Yong Zhi
authors.initials: YZ
authors.lastname: Foo
authors.affiliation: Department of Zoology, University of Otago, 340 Great King Street, Dunedin, 9016, New Zealand.|Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, UNSW Sydney, NSW, 2052, Australia.
authors.forename: Shinichi
authors.identifier: http://orcid.org/0000-0002-7765-5182
authors.initials: S
authors.lastname: Nakagawa
authors.affiliation: ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia.
authors.forename: Gillian
authors.initials: G
authors.lastname: Rhodes
authors.affiliation: ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia.|Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia, 6009, Australia.
authors.forename: Leigh W
authors.initials: LW
authors.lastname: Simmons
mesh_terms: D000818:Animals; D005260:Female; D012739:Gonadal Steroid Hormones / Q000276:immunology*; D007109:Immunity / Q000502:physiology*; D008297:Male
chemical_list: D012739:Gonadal Steroid Hormones
keywords: honest signals; immune function; immunocompetence handicap hypothesis; meta-analysis; oestrogen; secondary sexual traits; sex hormones; sexual selection; testosterone; trade-offs