Introduction

As awareness of environmental health inequities grows, a question remains as to whether vulnerable groups have been systematically excluded from the evidence base. Increasingly, researchers are raising concerns about environmental health issues that may disproportionately affect sexual and gender minority (SGM; generally including lesbian, gay, bisexual, transgender, and queer) populations. In 2022, the American Journal of Public Health published a special section on environmental justice that included 4 articles that explored intersections with SGM health.^1-4 Among those articles, Goldsmith and Bell proposed a conceptual framework to guide future environmental health research for SGM populations.² More recently, Bucher and colleagues highlighted how an intersectional approach to exposomics research could provide a framework for evaluating how environmental exposures interact with biological sex and gender identity to influence health.⁵ Additionally, several recent reviews have explored the impact of natural hazards⁶ and climate change^7,8 on SGM populations.

Despite growing attention and guiding frameworks, we still know very little about how environmental exposures may be contributing to the health inequities experienced by SGM people, especially exposures beyond psycho-behavioral mechanisms that have traditionally been viewed as the pathways between minority stress and negative health outcomes. While disparities related to psycho-behavioral mechanisms (eg, cigarette smoke) are well established in the existing literature, other environmental exposures likely also contribute to health inequities among SGM populations. To understand and effectively address these other exposures, we conducted a scoping review to determine the extent to which disparities in environmental exposures between SGM and non-SGM (ie, heterosexual and cisgender) populations have been measured in the United States. Establishing this empirical base of evidence is crucial to setting research agendas, equitably allocating funding and other resources, and advancing evidence-based policies and programs that promote environmental health equity for these populations.

Methods

We conducted a scoping review to identify available literature instead of a traditional systematic review to assess the quality of work conducted for several reasons. A scoping review is a relatively new approach designed to provide an overview of available evidence in response to a broad research question. Such a review is best suited when there is minimal research in an area; the review can begin to build the required knowledge base. Our goal was to identify the range of information available and to determine the extent to which disparities in environmental exposures have been measured between SGM and non-SGM populations in the United States. A protocol for conducting this review was prepared a priori based on the framework created by the Arksey and O’Malley⁹ and further refined based on guidance from the Joanna Briggs Institute.¹⁰ To ensure high rigor and replicability of our results, we adhered to the Preferred Items for Systematic Reviews and Meta-Analyses extension for scoping reviews (PRISMA-ScR) guidelines.¹¹

Search strategy

The study team worked in collaboration with a professional reference librarian to develop a search strategy to address relevant populations, exposures, and comparisons (3 of the 4 components of a PECO statement; Table 1); there were no restrictions on outcomes. The search terms included a combination of medical subject headings and free text words related to the following core concepts: gender and sexuality, environmental exposures, and United States.

Table 1.

PECO statement.

We focused our search on environmental exposures, defined by the National Cancer Institute as “chemical, biological, or physical substances found in air, water, food, or soil that may have a harmful effect on a person’s health.”¹² As our primary objective was to identify evidence of environmental exposures beyond the established psycho-behavioral mechanisms (eg, smoking), we neither included nor excluded any specific exposure types in our search terms. This approach enabled us to maintain a focus on environmental exposures broadly while still capturing studies on psycho-behavioral mechanisms when those mechanisms were framed as environmental health issues.

We further focused our search on environmental exposures within the United States. While there is value in having a global perspective with regards to environmental health issues, our objective was to establish an empirical evidence base that can galvanize domestic policymakers, public health officials, and funders to address the environmental health injustices experienced by SGM populations in the United States.

Finally, we focused our search on peer-reviewed articles published since January 1, 2011, the year that the Institute of Medicine published a comprehensive report summarizing the range of pervasive health disparities experienced by SGM individuals.¹³ This report served as a catalyst for funding and research to document the ways in which SGM people are disproportionately impacted by a range of negative health outcomes.

We concluded our search on September 4, 2024. We utilized PubMed, a database containing more than 37 million citations and abstracts of biomedical and life sciences literature. PubMed is maintained by the National Center for Biotechnology Information at the U.S. National Library of Medicine located at the National Institutes of Health. The final search terms are presented in their entirety in  Supplemental Table S1.

Results

The PubMed search generated a total 447 articles for title and abstract screening. Of the 447 articles identified, 395 articles were excluded based on title and abstract screening, leaving 52 articles for full-text review. Hand screening the bibliographies of these references resulted in an additional 10 articles to screen. In total, 62 articles were considered potentially relevant after title and abstract screening. After full-text review of all 62 articles, 12 articles remained for data extraction. This process is summarized in the PRISMA flowchart in Figure 1. An overview of extracted studies is presented in Table 2.

Figure 1.

Flowchart of studies through the review process.

Table 2.

Overview of studies examining differences in environmental exposures between SGM and non-SGM populations in the United States.

Only 2 studies from our review examined disparities in environmental exposures beyond psycho-behavioral mechanisms.^15,16 These studies, both by Collins and colleagues, drew on data from the U.S. Census, the American Community Survey, and the Environmental Protection Agency to examine the spatial relationships between same-sex partner households and cumulative cancer risk from exposure to hazardous air pollutants (HAPs). In 2016, Collins et al found that neighborhoods across Houston, Texas, with relatively high proportions of same-sex male partner households were associated with significantly greater exposure to cancer-causing HAPs; those with high proportions of same-sex female partner households were associated with less exposure.¹⁵ In a national study of HAPs the following year, the same authors found that, compared to their heterosexual peers, same-sex male and female couples had 12.3% and 23.8% higher cancer and respiratory risks, respectively.¹⁶

Of the remaining 10 articles eligible for data extraction, 8 examined disparities related to cigarette smoke exposure, including electronic cigarettes, between sexual minority and heterosexual populations.^17-24 In general, studies found that sexual minority people, including sexual minority youth, were more likely to smoke tobacco than their heterosexual counterparts.^{17,18,20,21,23} Compared to heterosexuals, sexual minority people also were more likely to be exposed to secondhand smoke (SHS) across various settings, including at home,²¹ in cars,²⁰ and outdoors.²² Note, disparities in smoking and SHS exposure were not universal across all settings or for all subgroups. For instance, King et al (2014) observed no significant differences between heterosexual and sexual minority respondents in the workplace.¹⁹

The remaining 2 studies from our review examined differences in UV radiation exposure between sexual minority and heterosexual populations.^25,26 Both studies found that sexual minority men were at higher risk for (exposure to UV radiation) compared to heterosexual men. In contrast, sexual minority status was a moderating variable for women.²⁵

Discussion

Our scoping review identified very few studies that have examined and documented environmental exposure disparities between SGM and non-SGM populations in the United States. These studies focused mostly on cigarette smoke exposures. None examined environmental exposure disparities between gender minority and cisgender populations.

Several factors likely contribute to limited number and scope of identified studies. First is a problem endemic to research with any relatively small population—obtaining a sample that can be generalized with confidence requires considerably more resources than are required for sampling the general population.¹³ The present review identified only 2 studies that collected primary data—one using time-space sampling to generate a sample of club-going adults (n = 618) in New York City, New York,¹⁸ and the other randomly sampling students (n = 1132) from a university in the southeastern United States.²³ Given the sample sizes and geographic concentrations of these studies, neither is likely to be generalizable to a broader context.

To address concerns about generalizability and statistical power, especially given scarce resources, researchers often conduct secondary analyses of existing health data collected from surveys of large state or national samples. Increasingly, state and federal surveys are collecting sexual orientation and gender identity data, including 11 surveys within the federal statistical system.²⁷ Despite progress toward the inclusion of these questions, we could not identify any nationally representative environmental health survey that included sexual orientation or gender identity questions.

In the absence of a nationally representative environmental health survey with sexual orientation and gender identity data, researchers have relied on surveys about general health behaviors and outcomes (eg, National Health Interview Survey, National Adult Tobacco Survey, Youth Risk Behavior Survey, National Health and Nutrition Examination Survey). As a result, studies on environmental exposures related to psycho-behavioral mechanisms (eg, cigarette smoke) are overrepresented in the literature. While the prevalence of tobacco use is significantly higher among SGM adults compared to their heterosexual counterparts,²⁸ the disproportionate focus on smoking and SHS exposure ignores other exposures and vulnerabilities likely to contribute to environmental injustices impacting this population.

In the short term, there are ways to grow the empirical evidence base at the intersection of environmental exposures and SGM health through secondary data analyses by advancing current study designs and measurement. For example, merging environmental data with other existing SGM population data can be an effective alternative for researchers struggling with underpowered analyses caused by low engagement with SGM individuals in cohort studies. Here, the methods employed by Collins et al can be useful.^15,16 By overlaying U.S. Census data with data from the Environmental Protection Agency, we can more immediately identify SGM inequities. We acknowledge this method likely will result in dramatic underestimates until the American Community Survey (ACS) expands beyond same-sex household data and begins collecting data on the sexual orientation and gender identity of respondents. The U.S. Census Bureau plans to test questions about sexual orientation and gender identity on the ACS this year.²⁹

Longer-term solutions require systematically including validated sexual orientation and gender identity measures across federal, state, and local datasets. Including these measures is essential for large-scale analysis of the environmental health issues that may disproportionately affect sexual and gender minority populations. These datasets should carefully capture nuanced aspects of 3 distinct concepts—sex, gender, and sexual orientation.³⁰ While current datasets capturing sexual orientation and gender identity data show that respondents are unlikely to skip questions related to these concepts, especially compared to other sensitive data items, researchers should utilize survey design elements (eg, emphasizing confidentiality and/or anonymity, leading up to sensitive questions, providing context) to reduce item nonresponse and minimize survey breakoffs.³¹ These datasets also should include measures that can be used to assess environmental exposures and intersectionality of risk.²

Note, researchers who rely upon federal, state, and local datasets that include sexual orientation and gender identity data must exercise caution when conducting secondary analysis. Even as these datasets expand, they likely will continue to strike a balance between providing response options that capture the full spectrum of sexual orientation and gender identity while also maintaining brevity and avoiding confusion among general populations. One common compromise has been to include “something else” and “don’t know” response options, as done on at least 8 federal surveys.³² More and more people, especially younger adults, are using diverse labels (eg, pansexual, queer) to describe their sexual orientation and gender identity.^33-35 Others are rejecting labels altogether.^36-38 Since corresponding response options are often unavailable on large population surveys, people are increasingly selecting “something else” or “don’t know.”³⁹ Attempting to identify and document disparities in environmental exposures without properly classifying these respondents likely impedes our ability to understand the magnitude and nature of health inequities among SGM populations.

Longer-term solutions also require additional resources to reduce reliance on existing datasets and enable researchers to collect their own data. The federal government is an obvious potential source for these resources, as all the studies in this review were supported, in whole or in part, with federal funding. Most of this funding was provided through a broad array of Institutes within the National Institutes of Health (NIH); however, no study from our review was funded by the National Institute for Environmental Health Sciences, the Institute responsible for discovering how the environment affects people in order to promote healthier lives. NIH and other federal funders should issue notices of special interest and requests for applications to stimulate research measuring and addressing environmental health inequities among SGM populations. Further, in addition to increased federal funding, promoting environmental health equity for SGM populations also will require investments from state and local governments as well as the private sector. Notably, the 2 studies that collected primary data also leveraged additional state or local funding.^18,23

Even with additional funding to identify and address the environmental health issues that may disproportionately affect SGM populations, resources will likely remain scarce. Consequently, researchers who are interested in this area, especially those who intend to generate primary data, must carefully design their studies to fully optimize research funding. When collecting sexual orientation and gender identity data, researchers must understand that these concepts are interrelated but conceptually distinct. Researchers should strive to fully understand nuanced aspects of sexual orientation, including identity, attraction, and behavior. This more comprehensive framing of sexual orientation can help identify people who may not identify as sexual minority but who may be attracted to or have sex with people of the same sex.² Likewise, researchers should consider capturing various dimensions of sex and gender (eg, sex assigned at birth, sex phenotype at birth, current gender identity, internalized gender roles, and externalized gender expressions) that may influence environmental exposures.⁴⁰

Additionally, studies designed for primary data collection should apply community-based participatory research approaches—whereby the affected community is meaningfully included at all stages of the research process—which has been shown to generate better science.⁴¹ Since SGM people often belong to other marginalized groups that are also particularly vulnerable to environmental injustices, these studies should incorporate intersectional approaches to examining disparities in environmental exposures.

Limitations

Our scoping review has several limitations. First, we did not assess the quality of the included studies. We also used only one database, PubMed, to identify these studies. While PubMed is arguably more comprehensive than any other database, we may have missed relevant literature that is only indexed elsewhere. Our decision to focus on environmental exposures broadly rather than enumerate specific exposure types means that we likely understated the scope of evidence related to psycho-behavioral mechanisms, especially exposures related to cigarette smoke. Relatedly, our decision to limit our search to environmental exposures within the United States ignores potentially relevant literature from other countries. Finally, the subjective nature of decisions related to study selection, inclusion criteria, and data interpretation may have introduced reviewer bias, affecting the comprehensiveness and reliability of the review. To mitigate these limitations, the study team carefully planned an extensive, a priori search criteria to answer the study question and utilized software to document a review process where all decisions were made by at least 2 reviewers working independently of each other.

Conclusion

This scoping review revealed a dearth of research on how environmental exposures contribute to health inequities for SGM populations compared to heterosexual and cisgender people. The existing research primarily focuses on cigarette smoke exposure, while studies on other harmful environmental exposures remain sparse. These findings highlight a critical gap in environmental health research for SGM populations. One short-term solution to address this gap is to merge existing environmental data (eg, data from the Environmental Protection Agency) with SGM population data. In the longer term, more state and national datasets must systematically include sexual orientation and gender identity, allowing for more robust secondary analysis. Ultimately, increased federal, state, and local funding to support primary research that explores diverse environmental exposures is essential for advancing health equity for SGM populations in the United States. This research should prioritize community-based participatory research principles and intersectional approaches to fully capture the vulnerabilities of these populations. Taken together, these efforts can significantly advance our ability to identify and address environmental health inequities experienced by SGM people.