Sex and gender analysis improves science and engineering

Solving gender gaps in health, what else is missing?

In recent years, a great deal of attention has been paid to gender inequities in health. However, while we have a good body of evidence on the impact of gender on the health and vulnerability of women and men, we have not yet been able to generate sufficient evidence on effective interventions that can transform this situation or can influence public health policy making. Only a limited number of educational interventions on gender-sensitivity, gender bias in clinical practice and policies to tackle gender inequalities in health have been formulated, implemented and evaluated. Even in the current pandemic situation caused by SARS-CoV2, we have seen the lack of gender mainstreaming reflected in the global response. This happens even when we have tools that facilitate the formulation and implementation of actions to reduce gender inequities in health. We consider that the current initiatives organized to carry out advocacy activities on gender inequity in health to be very positive. In the same line of these initiatives, we propose that while academic and institutional research on gender and health remains essential, we need to shift the focus towards action. In order to move forward, we need public health researchers questioning what public health practice need to do to address gender inequities and shake structural and social power inequities in order to increase the gender equity in health.

Reporting and misreporting of sex differences in the biological sciences

As part of an initiative to improve rigor and reproducibility in biomedical research, the U.S. National Institutes of Health now requires the consideration of sex as a biological variable in preclinical studies. This new policy has been interpreted by some as a call to compare males and females with each other. Researchers testing for sex differences may not be trained to do so, however, increasing risk for misinterpretation of results. Using a list of recently published articles curated by Woitowich et al. (eLife, 2020; 9:e56344), we examined reports of sex differences and non-differences across nine biological disciplines. Sex differences were claimed in the majority of the 147 articles we analyzed; however, statistical evidence supporting those differences was often missing. For example, when a sex-specific effect of a manipulation was claimed, authors usually had not tested statistically whether females and males responded differently. Thus, sex-specific effects may be over-reported. In contrast, we also encountered practices that could mask sex differences, such as pooling the sexes without first testing for a difference. Our findings support the need for continuing efforts to train researchers how to test for and report sex differences in order to promote rigor and reproducibility in biomedical research.

Biomedical research has a long history of including only men or male laboratory animals in studies. To address this disparity, the United States National Institutes of Health (NIH) rolled out a policy in 2016 called Sex as a Biological Variable (or SABV). The policy requires researchers funded by the NIH to include males and females in every experiment unless there is a strong justification not to, such as studies of ovarian cancer. Since then, the number of research papers including both sexes has continued to grow.

Although the NIH does not require investigators to compare males and females, many researchers have interpreted the SABV policy as a call to do so. This has led to reports of sex differences that would otherwise have been unrecognized or ignored. However, researchers may not be trained on how best to test for sex differences in their data, and if the data are not analyzed appropriately this may lead to misleading interpretations.

Here, Garcia-Sifuentes and Maney have examined the methods of 147 papers published in 2019 that included both males and females. They discovered that more than half of these studies had reported sex differences, but these claims were not always backed by statistical evidence. Indeed, in a large majority (more than 70%) of the papers describing differences in how males and females responded to a treatment, the impact of the treatment was not actually statistically compared between the sexes. This suggests that sex-specific effects may be over-reported. In contrast, Garcia-Sifuentes and Maney also encountered instances where an effect may have been masked due to data from males and females being pooled together without testing for a difference first.

These findings reveal how easy it is to draw misleading conclusions from sex-based data. Garcia-Sifuentes and Maney hope their work raises awareness of this issue and encourages the development of more training materials for researchers.

Is there a difference in the efficacy of COVID-19 vaccine in males and females? - A systematic review and meta-analysis

INTRODUCTION

Females generally have higher antibody responses to viral vaccines. Our objectives were to compare gender differences in the efficacy of COVID-19 vaccination.

METHODS

Data sources: Studies from PubMed, Embase, Cochrane Central Register, Web of Science, ClinicalTrials.gov, and the World Health Organization's International Clinical Trials Registry Platform.

RESULTS

We included four eligible trials; all were categorized as having a low risk of bias. COVID-19 vaccine was significantly effective in both males and females. Slightly more SARS-CoV-2 infections were recorded in females than in males, but the difference was not significant (RR 1.064 [0.888-1.274]; p = .502, I2 = 5.7%; p = .367, 643,127 participants).

CONCLUSION

Despite significant biological and behavioral differences between males and females, we found no significant gender differences in the efficacy of the COVID-19 vaccines, especially in younger populations. Further pragmatic trials are needed to confirm the gender differences in protective response of different types of vaccines to different age groups.

Oxytocin blood concentrations in alcohol use disorder: A cross-sectional, longitudinal, and sex-separated study

Alcohol use disorder (AUD) is a severe illness, for which we lack sufficient mechanistic understanding. Preliminary evidence associates AUD with the oxytocin (OXT) system. Here we investigated alterations in endogenous OXT blood concentrations in patients with AUD and their association with alcohol drinking and prospective course. In sex-separated analyses, OXT serum concentrations of 200 in-patients with AUD (56.5% male; baseline, 24-72 h of abstinence) were compared with those of 240 age-matched healthy controls (55.4% male), investigated longitudinally (follow-up, 5 days later), and tested for associations with alcohol drinking behavior and prospective 24-month alcohol-related hospital readmissions. At baseline, the patients showed increased OXT concentrations relative to controls (men, 156%, P < 0.001; women, 124%, P = 0.002). The elevations normalized at follow-up. In male patients, baseline OXT concentrations correlated positively with alcohol concentration at admission, the amount of alcohol consumption per drinking year, and the number of previous withdrawal treatments (Rho > 0.195, P < 0.044). In beverage type-specific analysis, baseline OXT concentrations correlated with liquor consumption positively in male and negatively in female patients (|Rho| > 0.277, P < 0.017). Higher baseline OXT concentrations predicted more readmissions and fewer days to the first readmission (|Rho| > 0.185, P < 0.050) in male patients. This study provides novel and sex-separated insights into the role of the OXT system in AUD. We identified a mechanism that might underlie the sex-separated choice of beverage type and established that increased OXT concentrations during early abstinence predict a worse outcome in male patients with AUD.

Improving clinical outcomes through attention to sex and hormones in research

Biological sex, fluctuations in sex steroid hormones throughout life and gender as a social construct all influence every aspect of health and disease. Yet, for decades, most basic and clinical studies have included only male individuals. As modern health care moves towards personalized medicine, it is clear that considering sex and hormonal status in basic and clinical studies will bring precision to the development of novel therapeutics and treatment paradigms. To this end, funding, regulatory and policy agencies now require inclusion of female animals and women in basic and clinical studies. However, inclusion of female animals and women often does not mean that information regarding potential hormonal interactions with pharmacological treatments or clinical outcomes is available. All sex steroid hormones can interact with receptors for drug targets, metabolism and transport. Genetic variation in receptors or in enzymatic function might contribute to sex differences in therapeutic efficacy and adverse drug reactions. Outcomes from clinical trials are often not reported by sex, and, if the data are available, they are not translated into clinical practice guidelines. This Review will provide a historical perspective for the current state of research related to hormone trials and provide concrete strategies that, if implemented, will improve the health of all people.

Measurement of glomerular filtration rate reveals that subcapsular injection of shear-thinning hyaluronic acid hydrogels does not impair kidney function in mice

The continued development of minimally invasive therapeutic implants, such as injectable hydrogels, necessitates the concurrent advancement of methods to best assess their biocompatibility via functional outcomes in vivo. Biomaterial implants have been studied to treat kidney disease; however, assessment of biocompatibility has been limited to biomarker and histological assessments. Techniques now exist to measure kidney function serially in vivo in murine studies via transcutaneous measurements of glomerular filtration rate (tGFR). In this study, adult male and female wild-type BalbC mice underwent right unilateral nephrectomy. The remaining solitary left kidney was allowed 4 weeks to recover via compensatory hypertrophy, after which subcapsular injection of either saline or shear-thinning hyaluronic acid hydrogel was performed. Serial tGFR measurements before and after treatment were used to assess the effect of hydrogel injection on kidney filtration. Urine and serum biomarkers of kidney function, and kidney histology were also quantified. Hydrogel injection did not affect kidney function, as assessed by tGFR. Results were in agreement with standard metrics of serum and urine biomarkers of injury as well as histological assessment of inflammation. The model developed provides a direct functional assessment of implant compatibility for the treatment of kidney disease and impact on kidney function.

Systematic Review of Sex and Gender Effects in Traumatic Brain Injury: Equity in Clinical and Functional Outcomes

Background: Although traumatic brain injury (TBI) is a leading cause of death and disability in male and female patients worldwide, little is known about the effect of sex and gender on TBI outcomes.

Objectives: This systematic review summarizes the evidence on the effect of sex and gender on core TBI outcomes.

Methods: All English-language studies from six literature databases that addressed core outcomes in adults with TBI and included sex or gender, TBI severity, and age in their analyses were considered eligible. Two reviewers extracted data, and two reviewers assessed study quality using tools recommended by the National Institutes of Health. The results were sorted according to time post-injury, injury severity, gender equity ranking of the study's country of origin, and outcomes studied. The results from the included studies were grouped based on the approach taken in reporting their respective findings.

Results and Limitations: Of 172 articles assessed, 58 studies were selected, comprising 1, 265, 955 participants with TBI (67% male across all studies) of all injury severities. All studies were conducted in countries with a very high or high human development index, while the Gender Inequality Index (GII) varied. While the heterogeneity across studies limited any meaningful conclusions with respect to the role of sex and gender, we did observe that as gender equality ranking improved, differences between male and female participants in outcomes would diminish. Inclusion of social equity parameters in the studies was limited.

Conclusions and Implications: The non-uniform findings observed bring forth the need to develop and use a comprehensive and consistent methodology in the study of sex and gender post-TBI, incorporating social equity parameters to uncover the potential social underpinnings of gender effects on health and functional outcomes.

Systematic Review Registration: CRD42018098697.

The Integration of Sex and Gender Considerations Into Biomedical Research: Lessons From International Funding Agencies

To improve the outcomes of research and medicine, government-based international research funding agencies have implemented various types of policies and mechanisms with respect to sex as a biological variable and gender as a sociocultural factor. After the 1990s, the US National Institutes of Health (NIH), the Canadian Institutes of Health Research (CIHR), and the European Commission (EC) began requesting that applicants address sex and gender considerations in grant proposals, and offering resources to help the scientific community integrate sex and gender into biomedical research. Although it is too early to analyze data on the success of all of the policies and mechanisms implemented, here we review the use both of carrots (incentives) and sticks (requirements) developed to motivate researchers and the entire scientific research enterprise to consider sex and gender influences on health and in science. The NIH focused on sex as a biological variable (SABV) aligned with an initiative to enhance reproducibility through rigor and transparency; CIHR instituted a sex- and gender-based analysis (SGBA) policy; and the EC required the integration of the "gender dimension," which incorporates sex, gender, and intersectional analysis into research and innovation. Other global efforts are briefly summarized. Although we are still learning what works, we share lessons learned to improve the integration of sex and gender considerations into research. In conjunction with refining and expanding the policies of funding agencies and mechanisms, private funders/philanthropic groups, editors of peer-reviewed journals, academic institutions, professional organizations, ethics boards, health care systems, and industry also need to make concerted efforts to integrate sex and gender into research, and we all must bridge across silos to promote systemwide solutions throughout the biomedical enterprise. For example, policies that encourage researchers to disaggregate data by sex and gender, the development of tools to better measure gender effects, or policies similar to SABV and/or SGBA adopted by private funders would accelerate progress. Uptake, accountability for, and a critical appraisal of sex and gender throughout the biomedical enterprise will be crucial to achieving the goal of relevant, reproducible, replicable, and responsible science that will lead to better evidence-based, personalized care for all, but especially for women.

Comparing axon regeneration in male and female mice after peripheral nerve injury

Axons in the adult mammalian central nervous system fail to regenerate after injury. By contrast, spontaneous axon regeneration occurs in the peripheral nervous system (PNS) due to a supportive PNS environment and an increase in the intrinsic growth potential induced by injury via cooperative activation of multifaceted biological pathways. This study compared axon regeneration and injury responses in C57BL/6 male and female mice after sciatic nerve crush (SNC) injury. The extent of axon regeneration in vivo was indistinguishable in male and female mice when observed at 3 days after SNC injury, and primary dorsal root ganglion (DRG) neurons from injured, male and female mice extended axons to a similar length. Moreover, the induction of selected regeneration-associated genes (RAGs), such as Atf3, Sprr1a, Gap43, Sox11, Jun, Gadd45a, and Smad1 were comparable in male and female DRGs when assessed by quantitative real-time reverse transcription polymerase chain reaction. Furthermore, the RNA-seq analysis of male and female DRGs revealed that differentially expressed genes (DEGs) in SNC groups compared to sham-operated groups included many common genes associated with neurite outgrowth. However, we also found that a large number of genes in the DEGs were sex dependent, implicating the involvement of distinct gene regulatory network in the two sexes following peripheral nerve injury. In conclusion, we found that male and female mice mounted a comparable axon regeneration response and many RAGs were commonly induced in response to SNC. However, given that many DEGs were sex-dependently expressed, future studies are needed to investigate whether they contribute to peripheral axon regeneration, and if so, to what extent.

Sex differences in economic decision-making: Exogenous estradiol has opposing effects on fairness framing in women and men

Burgeoning evidence indicates that women are more sensitive to the context of an offer and show a stronger propensity to adjust their behavior with changing fairness frames. We evaluated whether the sex hormone estradiol and associated stereotypical beliefs contribute to fairness framings by administering topical estradiol (2 mg) to 108 healthy women and 104 heathy men in a randomized, double-blind, placebo-controlled between-subject study design. Participants played the role of the responder in a modified version of the Ultimatum Game (UG), in which identical offers for the division of a given amount of money were framed as either fair or unfair. Furthermore, participants completed an unframed UG and a delayed discounting task to probe possible effects of estradiol on altruistic preferences and delay gratification. Our results show that women were more sensitive to fairness frames than men. Intriguingly, however, estradiol had sex-specific effects on fairness sensitivity by increasing the acceptance rate of proposals with a fair frame in men and reducing it in women. Furthermore, the mere belief of receiving estradiol treatment significantly increased the acceptance of unfair-framed offers in both sexes, but estradiol did not significantly alter the response to unframed offers and impulsive decision-making. Collectively, our findings indicate that estradiol has opposing effects on the sensitivity to the perceived fairness of economic offers in women and men. The profound effects of estradiol treatment and stereotypical beliefs provide support for the notion that sex differences in fairness framing are rooted in both biological and environmental factors.

The effect of patient sex on the efficacy and safety of anticancer immunotherapy

Introduction: Immune checkpoint inhibitors (ICIs) have improved the prognosis of patients with several types of cancer.A sex-based dimorphism in efficacy and toxicity of chemotherapies is well known and was recently described for anticancer immunotherapy.Areas covered: This review presents an overview of existing biological differences between males and females, including the immune system dimorphism, which represent the rationale for a sexual dimorphism in activity and toxicity of anticancer immunotherapies.Expert opinion: Clinical and preclinical research focused its efforts on the characterization of cancer molecular background and the complexity of tumoral microenvironment.Host factors, such as sex of a patient, and their potential roles in modulating cancer behavior as well as sensitivity and toxicity to anticancer treatments have been under-evaluated and poorly studied.Differences between males and females have been reported in studies with chemotherapy, both in activity and toxicity.Sex-based dimorphism is well known and relies on a complex interplay between immune functions, hormones, genes, and microbioma.With the extensive use of new drugs such as ICIs that lead to an immune system activation, the role of sex in modulating responses and immune-related toxicities needs to be taken into account to further tailor therapeutic approaches for males and females.

Progesterone serum levels correlate negatively with craving in female postmenopausal in-patients with alcohol use disorder: A sex- and menopausal status-separated study

OBJECTIVE

Alcohol use disorder (AUD) shows a high prevalence and often takes a severe and chronic course. However, the underlying mechanisms still need to be better understood. There is increasing evidence for a role of sex hormones in AUD and for the importance of sex-separated concepts in addiction research. Nevertheless, only few data give insight into how progesterone is involved in AUD.

METHOD

Serum progesterone levels were measured at baseline (during early abstinence) in 186 in-patients with AUD (19% premenopausal females, 20% postmenopausal females, 61% males) and at median 5 days later. They were compared with those of 233 healthy control subjects (24% premenopausal females, 19% postmenopausal females, 57% males). We quantified craving with the Obsessive Compulsive Drinking Scale (OCDS) and visual analogue scales (VAS). Alcohol-related hospital readmissions within a 24-month period following initial in-patient treatment were recorded. We conducted analyses separately for sex and for menopausal status in female participants.

RESULTS

Postmenopausal females with AUD reported higher craving than premenopausal females. In postmenopausal females, higher baseline progesterone levels correlated with lower OCDS total craving and VAS craving, i.e., lower state craving and lower average, maximum, and less frequent craving during withdrawal. In males with AUD, progesterone levels at baseline tended to be higher than in controls and declined to follow-up. Alcohol-related readmissions were not significantly associated with serum progesterone levels.

CONCLUSION

We provide first evidence that progesterone levels correlate with craving in females with AUD.

Sex-differences in symptoms and functioning in >5000 cancer survivors: Results from the PROFILES registry

BACKGROUND

Previous reports highlight the greater number of side effects that women experience during cancer treatment, but little is known about sex differences in symptoms and functioning in long-term survivors.

METHODS

We investigated sex differences in the prevalence of physical (EORTC QLQ-C30) and emotional symptoms (Hospital Anxiety and Depression Scale) and loss of functioning (EORTC QLQ-C30) in 5339 cancer survivors (55% males). General linear models were computed to assess the differences in symptoms and functioning between female and male cancer survivors and between survivors and an age-matched reference population.

RESULTS

The direct comparison between female and male cancer survivors identified more symptoms, such as nausea and vomiting (M = 5.0 versus. 3.2), insomnia (M = 26.1 versus. 15.9), anxiety (M = 5.2 versus. 4.2), and lower physical (M = 77.5 versus. 82.5) and emotional functioning (M = 83.4 versus. 86.3), in female survivors. However, comparison with an age-matched reference population demonstrated that several symptoms, such as fatigue, dyspnea, anxiety and depression, appeared to be more frequent in male patients. The investigation of functioning domains - compared with a reference population - highlighted further sex-specific differences. Female survivors experienced a moderate net loss in physical and cognitive functioning (-6.1 [95% CI = -8.1; -4,1] and -5.2 respectively [95% CI = -7; -3.5]), whereas male survivors displayed a significant net loss in role and social functioning compared to the reference population (-9.9 [95% CI = -11.2; -8.6] and -7.7 [95% CI = -9.6; -7.6] respectively).

CONCLUSION

To adequately capture sex differences in symptoms and functioning in long-term cancer survivors, a comparison with a reference population should always be considered. In our study population, this adjustment highlighted a significant and unexpected long-term impact on male patients. Role and social functioning were especially impacted in male patients, emphasizing the need to further investigate these gendered domains.

The anatomy of pain and suffering in the brain and its clinical implications

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Chronic pain, with a prevalence of 20-30 % is the major cause of human suffering worldwide, because effective, specific and safe therapies have yet to be developed. It is unevenly distributed among sexes, with women experiencing more pain and suffering. Chronic pain can be anatomically and phenomenologically dissected into three separable but interacting pathways, a lateral 'painfulness' pathway, a medial 'suffering' pathway and a descending pain inhibitory pathway. One may have pain(fullness) without suffering and suffering without pain(fullness). Pain sensation leads to suffering via a cognitive, emotional and autonomic processing, and is expressed as anger, fear, frustration, anxiety and depression. The medial pathway overlaps with the salience and stress networks, explaining that behavioural relevance or meaning determines the suffering associated with painfulness. Genetic and epigenetic influences trigger chronic neuroinflammatory changes which are involved in transitioning from acute to chronic pain. Based on the concept of the Bayesian brain, pain (and suffering) can be regarded as the consequence of an imbalance between the two ascending and the descending pain inhibitory pathways under control of the reward system. The therapeutic clinical implications of this simple pain model are obvious. After categorizing the working mechanisms of each of the available treatments (pain killers, psychopharmacology, psychotherapy, neuromodulation, psychosurgery, spinal cord stimulation) to 1 or more of the 3 pathways, a rational combination can be proposed of activating the descending pain inhibitory pathway in combination with inhibition of the medial and lateral pathway, so as to rebalance the pain (and suffering) pathways.

Long-term costs and cost-effectiveness of adjunctive corticosteroids for patients with septic shock in New Zealand

OBJECTIVE

The aim of the study was to determine whether adjunctive hydrocortisone reduced healthcare expenditure and was cost-effective compared with placebo in New Zealand patients in the Adjunctive Glucocorticoid Therapy in Patients with Septic Shock (ADRENAL) trial.

DESIGN

This is a health economic analysis using data linkage to New Zealand Ministry of Health databases to determine resource use, costs, and cost-effectiveness for a 24-month period.

SETTING

The study was conducted in New Zealand.

PARTICIPANTS AND INTERVENTION

Patients with septic shock were randomised to receive a 7-day continuous infusion of 200 mg of hydrocortisone or placebo in the ADRENAL trial.

MAIN OUTCOME MEASURES

Healthcare expenditure was associated with all hospital admissions, emergency department presentations, outpatient visits, and pharmacy expenditure. Effectiveness outcomes included mortality at 6 months and 24 months and quality of life at 6 months. Cost-effectiveness outcomes were assessed with reference to quality-adjusted life years gained at 6 months and life years gained at 24 months.

RESULTS

Of 3800 patients in the ADRENAL trial, 419 (11.0%) were eligible, and 405 (96.7% of those eligible) were included. The mean total costs per patient over 24 months were $143,627 ± 100,890 and $143,772 ± 97,117 for the hydrocortisone and placebo groups, respectively (p = 0.99). Intensive care unit costs for the index admission were $50,492 and $62,288 per patient for the hydrocortisone and placebo groups, respectively (p = 0.09). The mean number of quality-adjusted life years gained at 6 months and mean number of life years gained at 24 months was not significantly different by treatment group, and the probability of hydrocortisone being cost-effective was 55% at 24 months.

CONCLUSIONS

In New Zealand, adjunctive hydrocortisone did not reduce total healthcare expenditure or improve outcomes compared with placebo in patients with septic shock.

An assessment of statistical methods for non-independent data in ecological meta-analyses: Comment

Recently, Song et al. (2020) conducted a simulation study using different methods to deal with non-independence resulting from effect sizes originating from the same paper - a common occurrence in ecological meta-analyses. The main methods that were of interest in their simulations were: 1) a standard random-effects model used in combination with a weighted average effect size for each paper (i.e., a two-step method), 2) a standard random-effects model after randomly choosing one effect size per paper, 3) a multilevel (hierarchical) meta-analysis model, modelling paper identity as a random factor, and 4) a meta-analysis making use of a robust variance estimation method. Based on their simulation results, they recommend that meta-analysts should either use the two-step method, which involves taking a weighted paper mean followed by analysis with a random-effects model, or the robust variance estimation method.

Lack of consideration of sex and gender in COVID-19 clinical studies

Sex and gender differences impact the incidence of SARS-CoV-2 infection and COVID-19 mortality. Furthermore, sex differences influence the frequency and severity of pharmacological side effects. A large number of clinical trials to develop new therapeutic approaches and vaccines for COVID-19 are ongoing. We investigated the inclusion of sex and/or gender in COVID-19 studies on ClinicalTrials.gov, collecting data for the period January 1, 2020 to January 26, 2021. Here, we show that of the 4,420 registered SARS-CoV-2/COVID-19 studies, 935 (21.2%) address sex/gender solely in the context of recruitment, 237 (5.4%) plan sex-matched or representative samples or emphasized sex/gender reporting, and only 178 (4%) explicitly report a plan to include sex/gender as an analytical variable. Just eight (17.8%) of the 45 COVID-19 related clinical trials published in scientific journals until December 15, 2020 report sex-disaggregated results or subgroup analyses.

Discovering signaling mechanisms governing metabolism and metabolic diseases with Drosophila

There has been rapid growth in the use of Drosophila and other invertebrate systems to dissect mechanisms governing metabolism. New assays and approaches to physiology have aligned with superlative genetic tools in fruit flies to provide a powerful platform for posing new questions, or dissecting classical problems in metabolism and disease genetics. In multiple examples, these discoveries exploit experimental advantages as-yet unavailable in mammalian systems. Here, we illustrate how fly studies have addressed long-standing questions in three broad areas-inter-organ signaling through hormonal or neural mechanisms governing metabolism, intestinal interoception and feeding, and the cellular and signaling basis of sexually dimorphic metabolism and physiology-and how these findings relate to human (patho)physiology. The imaginative application of integrative physiology and related approaches in flies to questions in metabolism is expanding, and will be an engine of discovery, revealing paradigmatic features of metabolism underlying human diseases and physiological equipoise in health.

Identification and inclusion of gender factors in retrospective cohort studies: the GOING-FWD framework

Gender refers to the socially constructed roles, behaviours, expressions and identities of girls, women, boys, men and gender diverse people. Gender-related factors are seldom assessed as determinants of health outcomes, despite their powerful contribution. The Gender Outcomes INternational Group: to Further Well-being Development (GOING-FWD) project developed a standard five-step methodology applicable to retrospectively identify gender-related factors and assess their relationship to outcomes across selected cohorts of non-communicable chronic diseases from Austria, Canada, Spain, Sweden. Step 1 (identification of gender-related variables): Based on the gender framework of the Women Health Research Network (ie, identity, role, relations and institutionalised gender), and available literature for a certain disease, an optimal ‘wish-list’ of gender-related variables was created and discussed by experts. Step 2 (definition of outcomes): Data dictionaries were screened for clinical and patient-relevant outcomes, using the International Consortium for Health Outcome Measurement framework. Step 3 (building of feasible final list): a cross-validation between variables per database and the ‘wish-list’ was performed. Step 4 (retrospective data harmonisation): The harmonisation potential of variables was evaluated. Step 5 (definition of data structure and analysis): The following analytic strategies were identified: (1) local analysis of data not transferable followed by a meta-analysis combining study-level estimates; (2) centrally performed federated analysis of data, with the individual-level participant data remaining on local servers; (3) synthesising the data locally and performing a pooled analysis on the synthetic data and (4) central analysis of pooled transferable data. The application of the GOING-FWD multistep approach can help guide investigators to analyse gender and its impact on outcomes in previously collected data.

A 10-year longitudinal evaluation of science policy interventions to promote sex and gender in health research

BACKGROUND

Over the past decade, the Canadian Institutes of Health Research (CIHR) has implemented multicomponent interventions to increase the uptake of sex and gender in grant applications. Interventions included mandatory reporting on applicant forms, development of resources for applicants and evaluators, and grant review requirements. Here, we aim to inform science policy implementation by describing the 10-year outcomes and lessons learned from these interventions.

METHODS

This is a prospective longitudinal study. The population is all applicants across 15 investigator-initiated CIHR competitions from 2011 to 2019 and grant evaluators from 2018 to 2019. Quantitative data were derived from applicants' and grant evaluators' mandatory reporting of sex and gender integration in the grants management database. The application was the unit of analysis. Trends in sex and gender uptake in applications were plotted over time, stratified by research area. Univariate logistic regression was used to assess associations between the sex of the applicant and the uptake of sex and gender, and the latter with funding success. Qualitative review of the quality and appropriateness of evaluators' comments informed the development of discipline-specific training to peer review committee members. Feedback was compiled from a subset of evaluators on the perceived usefulness of the educational materials using a brief questionnaire.

RESULTS

Since 2011, 39,390 applications were submitted. The proportion that reported integration of sex rose from 22 to 83%, and gender from 12 to 33%. Population health research applications paid the greatest attention to gender (82%). Across every competition, applications with female principal investigators were more likely to integrate sex (odds ratio [OR] 1.60, 95% confidence interval [CI] 1.50-1.63) and gender (OR 2.40, 95% CI 2.29-2.51) than those who identified as male. Since 2018, applications that scored highly for the integration of sex (OR 1.92, 95% CI 1.50-2.50) and gender (OR 2.53, 95% CI 1.83-3.50) were more likely to be funded. Qualitative observations revealed persistent conflation of the terms sex and gender. Eighty-six percent of evaluators appreciated the tailored discipline-specific coaching.

CONCLUSIONS

A number of policy interventions improved sex and gender uptake in grant applications, with higher success rates observed over time for applications that integrated sex and gender. Other funders' action plans around sex and gender integration may be informed from our experiences of the timing, type and targets of the different interventions, specifically those directed at evaluators.

Equity for excellence in academic institutions: a manifesto for change

Higher academic institutions in the UK need to drive improvements in equity, diversity, and inclusion (EDI) through sustainable practical interventions. A broad view of inclusivity is based on an intersectional approach that considers race, geographical location, caring responsibilities, disability, neurodiversity, religion, and LGBTQIA+ identities. We describe the establishment of a diverse stakeholder group to develop practical grass-roots recommendations through which improvements can be advanced. We have developed a manifesto for change, comprising six domains through which academic institutions can drive progress through setting short, medium, and long-term priorities. Interventions will yield rewards in recruitment and retention of a diverse talent pool, leading to enhanced impact and output.

Sex Selection Bias in Schizophrenia Antipsychotic Trials—An Update Systematic Review

The lack of female participation in antipsychotic trials for schizophrenia poses an important issue regarding its applicability, with direct and real-life repercussions to clinical practice. Here, our aim is to systematically review the sampling sex bias among randomized clinical trials (RCTs) of second-generation antipsychotics—namely risperidone, olanzapine, quetiapine, ziprasidone, and aripiprazole—as an update to a previous 2005 review. We searched MEDLINE and the Cochrane database for studies published through 7 September 2020 that assessed adult samples of at least 50 subjects with a diagnosis of schizophrenia, schizophrenia spectrum disorder, or broad psychosis, in order to investigate the percentage of women recruited and associated factors. Our review included 148 RCTs, published from 1993 to 2020, encompassing 43,961 subjects. Overall, the mean proportion of women was 34%, but only 17 trials included 50% or more females. Younger samples, studies conducted in North America, pharmaceutical funding and presence of specific exclusion criteria for women (i.e., pregnancy, breast-feeding or lack of reliable contraceptive) were associated with a lower prevalence of women in the trials. Considering the possible different effects of antipsychotics in both sexes, and our lack of knowledge on the subject due to sampling bias, it is imperative to expand actions aimed at bridging this gap.

Abnormal subgenual anterior cingulate circuitry is unique to women but not men with chronic pain

The subgenual anterior cingulate cortex (sgACC) plays an important role in pain modulation. We previously demonstrated sex differences in sgACC functional connectivity (FC) in healthy individuals. Given that many chronic pain conditions show sex differences in prevalence, here we tested the hypothesis that people with chronic pain exhibit a sex-specific pattern of abnormal sgACC FC. We acquired resting-state functional magnetic resonance imaging data from 156 (82 W: 74 M) healthy participants and 38 (19 W: 19 M) people with chronic low back pain resulting from ankylosing spondylitis, a condition that predominantly affects men. We confirmed that there are sex differences in sgACC FC in our large cohort of healthy adults; women had greater sgACC FC with the precuneus, a key node of the default mode network, and men had greater sgACC FC with the posterior insula and the operculum. Next, we identified an interaction effect between sex and pain status (healthy/chronic pain) for sgACC FC. Within the chronic pain group, women had greater sgACC FC than men to the default mode and sensorimotor networks. Compared to healthy women, women with chronic pain also had greater sgACC FC to the precuneus and lower FC to the hippocampus and frontal regions. No differences in sgACC FC were seen in men with vs without chronic pain. Our findings indicate that abnormal sgACC circuitry is unique to women but not men with ankylosing spondylitis-related chronic pain. These sex differences may impact the benefit of therapeutics that target the sgACC for chronic pain.

Meta-analysis of variation suggests that embracing variability improves both replicability and generalizability in preclinical research

The replicability of research results has been a cause of increasing concern to the scientific community. The long-held belief that experimental standardization begets replicability has also been recently challenged, with the observation that the reduction of variability within studies can lead to idiosyncratic, lab-specific results that cannot be replicated. An alternative approach is to, instead, deliberately introduce heterogeneity, known as "heterogenization" of experimental design. Here, we explore a novel perspective in the heterogenization program in a meta-analysis of variability in observed phenotypic outcomes in both control and experimental animal models of ischemic stroke. First, by quantifying interindividual variability across control groups, we illustrate that the amount of heterogeneity in disease state (infarct volume) differs according to methodological approach, for example, in disease induction methods and disease models. We argue that such methods may improve replicability by creating diverse and representative distribution of baseline disease state in the reference group, against which treatment efficacy is assessed. Second, we illustrate how meta-analysis can be used to simultaneously assess efficacy and stability (i.e., mean effect and among-individual variability). We identify treatments that have efficacy and are generalizable to the population level (i.e., low interindividual variability), as well as those where there is high interindividual variability in response; for these, latter treatments translation to a clinical setting may require nuance. We argue that by embracing rather than seeking to minimize variability in phenotypic outcomes, we can motivate the shift toward heterogenization and improve both the replicability and generalizability of preclinical research.

Exploring the Food and Drug Administration's review and approval of Entresto (sacubitril/valsartan)

Federal regulatory agencies such as the United States Food and Drug Administration review pharmacological evidence to ensure the safety and efficacy of new and repurposed pharmaceuticals prior to market approval. The discussions, disagreements and procedural decisions contained within such reviews offer unique insight into a pharmaceutical's strengths, weaknesses and opportunities, yet are often overlooked as a significant source of pharmacological information for research and development. To highlight the value of such resources, we present a case study on Entresto, a first-in-class angiotensin receptor-neprilysin inhibitor for the treatment of heart failure with reduced ejection fraction, and explore the regulatory rationale underlying its market approval. Using information extracted from Entresto's online approval package at Drugs@FDA, we explore some of the procedural complexities underlying market approval of new pharmaceuticals, discuss the broad pharmacological implications contained within regulatory agency grey literature, and highlight opportunities for future therapeutic development.

Body mass index and serum levels of soluble leptin receptor are sex-specifically related to alcohol binge drinking behavior

OBJECTIVE

Binge drinking is a highly prevalent behavior in adolescents and young adults and a risk factor to develop alcohol use disorder. Body mass index (BMI) and blood levels of leptin peptide and its soluble receptor have been implicated in alcohol use disorder; however, their role in binge drinking remains to be investigated.

METHOD

We studied associations of BMI, serum levels of soluble leptin receptor (ObRe) and leptin as well as the free leptin index with binge drinking in 93 male and 99 female young adults.

RESULTS

In men, binge drinkers showed significantly higher BMI (kg/m²) than non-binge drinkers (23.67 vs. 22.08) and higher BMI correlated significantly with more severe binge drinking episodes (ρ = 0.251). In women, we found significantly higher ObRe (ng/ml) / BMI (kg/m²) values in binge drinkers than in non-binge drinkers (0.52 vs. 0.44) and ObRe/BMI values correlated significantly with more severe binge drinking episodes (ρ = 0.210).

CONCLUSION

This study confirms that higher BMI associates with binge drinking in men and shows for the first time a role of ObRe/BMI in binge drinking in women. Our data emphasize the importance of further research in the field of metabolic markers and implications in neurobiological processes of binge drinking.

Ensuring that biomedical AI benefits diverse populations

Artificial Intelligence (AI) can potentially impact many aspects of human health, from basic research discovery to individual health assessment. It is critical that these advances in technology broadly benefit diverse populations from around the world. This can be challenging because AI algorithms are often developed on non-representative samples and evaluated based on narrow metrics. Here we outline key challenges to biomedical AI in outcome design, data collection and technology evaluation, and use examples from precision health to illustrate how bias and health disparity may arise in each stage. We then suggest both short term approaches-more diverse data collection and AI monitoring-and longer term structural changes in funding, publications, and education to address these challenges.

Social Perception and Academic Trends on Women in the Field of Neurosurgery: A Bibliometric Analysis

BACKGROUND

The ongoing trend of societal evolution in contemporary civilization has allowed increased inclusion of heterogenous identity groups into fields, such as neurosurgery, where certain groups have traditionally been underrepresented. In regard to the field of neurosurgery, the increasing recognition of the disparities faced by women is illustrated by a growing body of academic literature.

METHODS

We conducted a bibliometric analysis querying the PubMed, Web of Science, Scopus, and Embase databases for articles on women in neurosurgery using the MeSH terms "woman," "women," "gender," neurosurgery," neurological surgery," and "neurosurgeon." Articles were excluded if they did not concern societal impact of nonmale population in the context of neurosurgery. Total citations, mean citations per year, publishing journal information, and author demographics were abstracted from included reports. Associations between abstracted continuous variables were evaluated using the Pearson correlation coefficient. Derived P values < 0.05 were taken as significant.

RESULTS

A total of 49 articles were included. Total numbers of citations per report were positively associated with mean citations per year (r = 0.7289, P = 0.0253), the latter of which was slightly negatively associated with the age of the report (r = -0.0413, P = 0.0009). Age of publication year was found to be negatively correlated with the number of reports published per year (r = -0.648, P = 0.0066). Total citations per reports were significantly correlated with increased numbers of citations during the last completed calendar year (2019: r = 0.8956, P = 0.0397).

CONCLUSIONS

Recognition in societal evolutionary trends as evidenced by academic activity has shown increased focus on the explicit and intrinsic biases faced by women in neurosurgery. Recent years have seen significant increases in published reports concerning the subject, as well as rising academic impact per a given report. This phenomenon is speculated to continue, and understanding to broaden as societal perception continues to develop.

Considering sex as a biological variable will require a global shift in science culture

For over half a century, male rodents have been the default model organism in preclinical neuroscience research, a convention that has likely contributed to higher rates of misdiagnosis and adverse side effects from drug treatment in women. Studying both sexes could help to rectify these public health problems, but incentive structures in publishing and career advancement deter many researchers from doing so. Moreover, funding agency directives to include male and female animals and human participants in grant proposals lack mechanisms to hold recipients accountable. In this Perspective, we highlight areas of behavioral, cellular and systems neuroscience in which fundamental sex differences have been identified, demonstrating that truly rigorous science must include males and females. We call for a cultural and structural change in how we conduct research and evaluate scientific progress, realigning our professional reward systems and experimental standards to produce a more equitable, representative and therefore translational body of knowledge.

An efficient new assay for measuring zebrafish anxiety: Tall tanks that better characterize between-individual differences

BACKGROUND

Zebrafish (Danio rerio) are increasingly being used to model anxiety. A common behavioral assay employed for assessing anxiety-like behaviors in zebrafish is the "novel tank test". We hypothesized that using deeper tanks in this test would result in greater between-individual variation in behavioral responses and a more 'repeatable' assay.

NEW METHODS

After mapping the literature and identifying common behavioral parameters used in analysis, we performed novel tank anxiety tests in both custom-designed 'tall' tanks with increased depth and 'short' trapezoidal tanks. We compared the repeatability of the behavioral parameters between tall and short tanks and also investigated sex differences.

RESULTS

Overall, regardless of tank depth, almost all behavioral parameters associated with anxiety in zebrafish were significantly repeatable (R = 0.24 to 0.60). Importantly, our tall tanks better captured between-individual differences, resulting in higher repeatability estimates (average repeatability tall tanks: R = 0.46; average repeatability short tanks: R = 0.36) and clearer sex differences.

CONCLUSIONS

Our assay using tall tanks has advantages over tests based on short tanks which underestimate repeatability. We argue that use of deeper tanks will improve the reliability of behavioral data across studies using novel tank tests for zebrafish. Our results also call for increased attention in designing the most appropriate assay in biomedical and behavioral sciences as current methods may lack the sensitivity to detect subtle, yet important, information, such as between-individual variation, an important component in assessing the reliability of behavioral data.

Impacts of high fat diet on ocular outcomes in rodent models of visual disease

High fat diets (HFD) have been utilized in rodent models of visual disease for over 50 years to model the effects of lipids, metabolic dysfunction, and diet-induced obesity on vision and ocular health. HFD treatment can recapitulate the pathologies of some of the leading causes of blindness, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) in rodent models of visual disease. However, there are many important factors to consider when using and interpreting these models. To synthesize our current understanding of the importance of lipid signaling, metabolism, and inflammation in HFD-driven visual disease processes, we systematically review the use of HFD in mouse and rat models of visual disease. The resulting literature is grouped into three clusters: models that solely focus on HFD treatment, models of diabetes that utilize both HFD and streptozotocin (STZ), and models of AMD that utilize both HFD and genetic models and/or other exposures. Our findings show that HFD profoundly affects vision, retinal function, many different ocular tissues, and multiple cell types through a variety of mechanisms. We delineate how HFD affects the cornea, lens, uvea, vitreous humor, retina, retinal pigmented epithelium (RPE), and Bruch's membrane (BM). Furthermore, we highlight how HFD impairs several retinal cell types, including glia (microglia), retinal ganglion cells, bipolar cells, photoreceptors, and vascular support cells (endothelial cells and pericytes). However, there are a number of gaps, limitations, and biases in the current literature. We highlight these gaps and discuss experimental design to help guide future studies. Very little is known about how HFD impacts the lens, ciliary bodies, and specific neuronal populations, such as rods, cones, bipolar cells, amacrine cells, and retinal ganglion cells. Additionally, sex bias is an important limitation in the current literature, with few HFD studies utilizing female rodents. Future studies should use ingredient-matched control diets (IMCD), include both sexes in experiments to evaluate sex-specific outcomes, conduct longitudinal metabolic and visual measurements, and capture acute outcomes. In conclusion, HFD is a systemic exposure with profound systemic effects, and rodent models are invaluable in understanding the impacts on visual and ocular disease.

Gender-related variables for health research

Background

In this paper, we argue for Gender as a Sociocultural Variable (GASV) as a complement to Sex as a Biological Variable (SABV). Sex (biology) and gender (sociocultural behaviors and attitudes) interact to influence health and disease processes across the lifespan—which is currently playing out in the COVID-19 pandemic. This study develops a gender assessment tool—the Stanford Gender-Related Variables for Health Research—for use in clinical and population research, including large-scale health surveys involving diverse Western populations. While analyzing sex as a biological variable is widely mandated, gender as a sociocultural variable is not, largely because the field lacks quantitative tools for analyzing the influence of gender on health outcomes.

Methods

We conducted a comprehensive review of English-language measures of gender from 1975 to 2015 to identify variables across three domains: gender norms, gender-related traits, and gender relations. This yielded 11 variables tested with 44 items in three US cross-sectional survey populations: two internet-based (N = 2051; N = 2135) and a patient-research registry (N = 489), conducted between May 2017 and January 2018.

Results

Exploratory and confirmatory factor analyses reduced 11 constructs to 7 gender-related variables: caregiver strain, work strain, independence, risk-taking, emotional intelligence, social support, and discrimination. Regression analyses, adjusted for age, ethnicity, income, education, sex assigned at birth, and self-reported gender identity, identified associations between these gender-related variables and self-rated general health, physical and mental health, and health-risk behaviors.

Conclusion

Our new instrument represents an important step toward developing more comprehensive and precise survey-based measures of gender in relation to health. Our questionnaire is designed to shed light on how specific gender-related behaviors and attitudes contribute to health and disease processes, irrespective of—or in addition to—biological sex and self-reported gender identity. Use of these gender-related variables in experimental studies, such as clinical trials, may also help us understand if gender factors play an important role as treatment-effect modifiers and would thus need to be further considered in treatment decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-021-00366-3.

The Importance of Gender to Understand Sex Differences in Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. There is robust evidence of heterogeneity in underlying mechanism, manifestation, prognosis, and response to treatment of CVD between male and female patients. Gender, which refers to the socially constructed roles, behaviours, expressions, and identities of individuals, is an important determinant of CV health, and its consideration might help in attaining a broader understanding of the observed sex differences in CVD. Established risk factors such as hypertension, dyslipidemia, diabetes mellitus, obesity, and smoking are well known to contribute to CVD. However, despite the differences in CVD risk between male and female, most studies looking into the magnitude of effect of each risk factor have traditionally focused on male subjects. While biological sex influences disease pathophysiology, the psycho-socio-cultural construct of gender can further interact with this effect. Behavioural, psychosocial, personal, cultural, and societal factors can create, repress, or strengthen underlying biological CV health differences. Although mechanisms of action are largely unclear, it is suggested that gender-related factors can further exacerbate the detrimental effect of established risk factors of CVD. In this narrative review, we explore the current literature investigating the role of gender in CV risk and its impact on established risk factors as a fundamental step toward precision medicine.

COVID-19 gender policy changes support female scientists and improve research quality

With more time being spent on caregiving responsibilities during the COVID-19 pandemic, female scientists' productivity dropped. When female scientists conduct research, identity factors are better incorporated in research content. In order to mitigate damage to the research enterprise, funding agencies can play a role by putting in place gender equity policies that support all applicants and ensure research quality. A national health research funder implemented gender policy changes that included extending deadlines and factoring sex and gender into COVID-19 grant requirements. Following these changes, the funder received more applications from female scientists, awarded a greater proportion of grants to female compared to male scientists, and received and funded more grant applications that considered sex and gender in the content of COVID-19 research. Further work is urgently required to address inequities associated with identity characteristics beyond gender.

Sex and gender differences in cognitive and brain reserve: Implications for Alzheimer's disease in women

Women represent ⅔ of the cases of Alzheimer's disease (AD). Current research has focused on differential risks to explain higher rates of AD in women. However, factors that reduce risk for AD, like cognitive/brain reserve, are less well explored. We asked: what is known about sex and gender differences in how reserve mitigates risk for AD? We conducted a narrative review of the literature, with keywords: "sex/gender differences", "cognitive/brain reserve", "Alzheimer's Disease", and the following cognitive reserve contributors: "education", "IQ", "occupation", "cognitive stimulation", "bilingualism", "socioeconomic status", "physical activity", "social support". Sixteen papers disaggregated their data by sex. Those papers observed sex and gender differences in reserve contributors. There is also evidence that greater reserve may be more beneficial in lowering AD risk in women, although more research is needed. We discuss how traditional reserve contributors are gendered and may not capture factors that support cognition in aging women.

Let's Talk About Sex-Biological Sex Is Underreported in Biomaterial Studies

Precision medicine aims to better individualize healthcare. It requires that biomaterials be designed for the physiological characteristics of a specific patient. To make this a reality, biomaterials research and development must address differences of biological sex. More specifically, biomaterials should be designed with properties optimized and appropriate for male and female patients. In analyzing research articles from seven prominent biomaterials journals, sex as a biological variable is missing from an overwhelming majority of in vitro biomaterial studies. From the survey, the reporting of the sex of primary cell cultures happened only 10.3% of the time. Contributing to this trend is that commercial vendors bias cell lines toward one sex or another by not disclosing information of cell line sex at the time of purchase; researchers do not communicate this pertinent information in published studies; and many journal policies have little to no requirements for reporting cell line characteristics. Omitting this valuable information leads to a gap in the understanding of sex-specific cell-biomaterial interactions and it creates a bias in research findings towards one sex or another. To curb this concerning trend and make precision biomaterials a reality will require the biomaterials field to "talk about sex" by reporting cell sex more broadly.

Accountability in protection of children against violence: Monitoring and measurement

Violence against children (VAC) is a pervasive and persistent injustice around the world. Thirty years after the adoption of the United Nations Convention on the Rights of the Child (CRC), the right of children to be protected against all forms of violence is still routinely violated. It is only within the last twenty years that the scope of this problem has been studied; as many point out, understanding the scope of the problem through comprehensive data collection is necessary to improve child protection. Data collection and data quality have improved drastically over this time. The Office of the High Commissioner on Human Rights recommends using comprehensive indicator systems that collect data on States Parties' structure- and process-related commitments to fulfil human rights, and on the outcomes of these commitments. However, most existing indicator sets on VAC fall short of this comprehensive approach, often focusing only on structural or outcome indicators. An international team of child rights experts is now developing GlobalChild, which will be an online platform consisting of comprehensive sets of structure-, process-, and outcome-related indicators for all 41 substantive rights of the CRC. This system will advance data collection, facilitate the monitoring function of the Committee on the Rights of the Child, and enable research on many rights of children, including their right to protection against violence. VAC is a complex problem, and protection against VAC is a right that is indivisible from other rights under the CRC. Therefore, a comprehensive and systematic approach is required to improve accountability to children around the world.

Thirty years of the CRC: Child protection progress, challenges and opportunities

The CRC has a challenging and ambitious agenda in relation to the protection of children from all forms of violence, particularly the large and increasing numbers of children affected by natural disasters, armed conflict, trafficking, poverty and increasing inequality, displacement and trafficking. In this article, we outline some of the issues in the implementation and understanding of the Convention and highlight three major international developments over the last decade: the adoption of General Comment No 13, the work of the Special Representative of the Secretary General on Violence Against Children, and the adoption of the 2030 Agenda for Sustainable Development by the UN General Assembly in 2005. We also identify four broad domains in which the Convention can and is being used to enhance efforts to ensure the protection of children based on a rights framework - advocacy and litigation, policy design, service delivery and research and monitoring methodology - rather than a welfare-based approach. The key to a rights-based approach in efforts to protect children is a focus on children's right to be involved in decision-making - and in research - that affect their lives.

Sexual dimorphism in trait variability and its eco-evolutionary and statistical implications

Biomedical and clinical sciences are experiencing a renewed interest in the fact that males and females differ in many anatomic, physiological, and behavioural traits. Sex differences in trait variability, however, are yet to receive similar recognition. In medical science, mammalian females are assumed to have higher trait variability due to estrous cycles (the ‘estrus-mediated variability hypothesis’); historically in biomedical research, females have been excluded for this reason. Contrastingly, evolutionary theory and associated data support the ‘greater male variability hypothesis’. Here, we test these competing hypotheses in 218 traits measured in >26,900 mice, using meta-analysis methods. Neither hypothesis could universally explain patterns in trait variability. Sex bias in variability was trait-dependent. While greater male variability was found in morphological traits, females were much more variable in immunological traits. Sex-specific variability has eco-evolutionary ramifications, including sex-dependent responses to climate change, as well as statistical implications including power analysis considering sex difference in variance.

Males and females differ in appearance, physiology and behavior. But we do not fully understand the health and evolutionary consequences of these differences. One reason for this is that, until recently, females were often excluded from medical studies. This made it difficult to know if a treatment would perform as well in females as males. To correct this, organizations that fund research now require scientists to include both sexes in studies. This has led to some questions about how to account for sex differences in studies.

One reason females have historically been excluded from medical studies is that some scientists assumed that they would have more variable responses to a particular treatment based on their estrous cycles. Other scientists, however, believe that males of a given species might be more variable because of the evolutionary pressures they face in competing for mates. Better understanding how males and females vary would help scientists better design studies to ensure they provide accurate answers.

Now, Zajitschek et al. debunk both the idea that males are more variable and the idea that females are more variable. To do this, Zajitschek et al. analyzed differences in 218 traits, like body size or certain behaviors, among nearly 27,000 male and female mice. This showed that neither male mice nor female mice were universally more different from other mice of their sex across all features. Instead, sex differences in how much variation existed in male or female mice depended on the individual trait. For example, males varied more in physical features like size, while females showed more differences in their immune systems.

The results suggest it is particularly important to consider sex-specific variability in both medical and other types of studies. To help other researchers better design experiments to factor in such variability, Zajitschek et al. created an interactive tool that will allow scientists to look at sex-based differences in individual features among male or female mice.