Sex Bias in Basic and Preclinical Noise-Induced Hearing Loss Research

INTRODUCTION: Sex differences in brain biochemistry, physiology, structure, and function have been gaining increasing attention in the scientific community. Males and females can have different responses to medications, diseases, and environmental variables. A small number of the approximately 7500 studies of noise-induced hearing loss (NIHL) have identified sex differences, but the mechanisms and characterization of these differences have not been thoroughly studied. The National Institutes of Health (NIH) issued a mandate in 2015 to include sex as a biological variable in all NIH-funded research beginning in January 2016. MATERIALS AND METHODS: In the present study, the representation of sex as a biological variable in preclinical and basic studies of NIHL was quantified for a 5-year period from January 2011 to December 2015 prior to the implementation of the NIH mandate. RESULTS: The analysis of 210 basic and preclinical studies showed that when sex is specified, experiments are predominantly performed on male animals. DISCUSSION: This bias is present in studies completed in the United States and foreign institutions, and the proportion of studies using only male participants has actually increased over the 5-year period examined. CONCLUSION: These results underscore the need to invest resources in studying NIHL in both sexes to better understand how sex shapes the outcomes and to optimize treatment and prevention strategies.