Comparison of depressive symptoms and inflammation between sexual minorities and heterosexuals using NHANES study of 8538 participants

The present study aims to compare the rate of depressive symptoms and inflammation levels between sexual minorities and heterosexuals. Data were obtained from the National Health and Nutrition Examination Survey from 2005 to 2010. Depressive-related symptoms were measured using the Patient Health Questionnaire-9 scoring system. C-reactive protein was analyzed with the Behring Nephelometer. Of 8538 participants, 95.8% self-reported as heterosexual and 4.2% as sexual minority. Depressive symptoms were reported in 7.1% of heterosexuals compared to 15.8% in sexual minorities (P = 0.001). In heterosexuals, C-reactive protein was higher in those with depressive symptoms compared to those without (P < 0.001). In sexual minorities, similar results were found, however, it was statistically insignificant. The intersection group of black sexual minority females reported the highest rate of depressive symptoms at 33.4%. We found that depressive symptoms were higher in sexual minorities compared to heterosexuals. Furthermore, systemic inflammation was highest in the intersection group of black sexual minority females.

Inclusion/exclusion criteria. We elected to include participants aged 20-59 (N = 9404) years since this group responded to sexual behavior and smoking behavior questionnaires. From this we excluded female participants who were pregnant (431). Individuals with missing information on depressive symptoms (20), marital status (7), education (7), body mass index (45) demographic, socioeconomic characteristics, CRP levels (349), self-identified sexual orientation, and depressive-related symptoms (20) were excluded from our analysis. Since prior studies have shown that abnormally high CRP levels have been associated with active infection instead of chronic inflammation, we also excluded those with CRP ≥ 10 mg/dL (7) from our analytic dataset. After incorporating the exclusion criteria our final analytic dataset came out to be 8,538.
Outcomes and measures. Individuals were defined collectively as sexual minority if they self-reported their sexual orientation as either gay, lesbian, or bisexual. Depressive-related symptoms were measured based on the nine-item Patient Health Questionnaire (PHQ-9) using a scoring system ranging from 0 (not at all) to 3 (nearly every day). Participants with a score ≥ 10 indicate depressive symptoms 8 . CRP, a serum inflammatory biomarker, was analyzed with the Behring Nephelometer using anti-CRP antibody latex particles. Participants' age was dichotomized using the median value, 40 years. Race was categorized as non-Hispanic white, non-Hispanic black, Hispanic, and another race (includes Asian race, mixed race, and other race). Individual's level of education in our cohort was grouped as less than high school, high school, and above high school. To define income levels, we used the poverty-income ratio (PIR) which is the ratio of family income to poverty threshold. Using this ratio and the U.S Census definition of income categories, we categorized income levels as poverty (PIR < 1), low income (1.0 ≤ PIR < 2.0), middle income (2.0 ≤ PIR < 4.0), and high income (PIR ≥ 4.0). We elected to combine "poverty" and "low income" groups for our analysis. In our analysis marital status was grouped as "single", "married or with partner", "divorced or separated or widowed. " Participants' smoking status was either reported as a current, former, or non-smoker. Based on CDC on defining body mass index (BMI) categories, we categorized this variable as underweight (< 18.5 kg/m 2 ), normal (18.5-24.9 kg/m 2 ), overweight (25.0-29.9 kg/ m 2 ), and obese (≥ 30.0 kg/m 2 ).
Data analysis. Using SAS Enterprise Guide Version 7.1 (SAS Institute Inc., Cary, NC, USA), chi-square, t-tests, and multivariate logistic regression were employed for statistical methods. Incorporating cluster, strata, and weighted variables in our analysis accounted for sampling weights and complexity of survey design and ensured that the oversampling of any groups did not occur. Covariates for the multivariable logistic regression model were determined by conducting bi-variable chi-square tests. Variables found to be significantly associated with depressive symptoms were included as a covariate. Associations were considered to be statistically significant if the two-sided P-value is 0.05 or less. NHANES data is publicly available and the datasets used in this study can be found online.
Consent to participate/Consent to publish. This study was deemed exempt from IRB approval as it contains de-identified information.
Human and animal rights. All statistical methods for this NHANES study were conducted in accordance with the Declaration of Helsinki.

Discussion
Sexual minorities reported more depressive symptoms compared to heterosexuals. Of note, nearly one-third of the female Black sexual minority intersection group had depressive symptoms. Furthermore, sexual minorities with depressive symptoms had significantly higher inflammation expressed by C-reactive protein.
Our results found that sexual minority individuals had more depressive symptoms. Others have also found that depression was significantly higher in LGBT individuals compared to heterosexuals 11 . This finding supports the minority stress theory, as described by Brooks, which postulates that exposure to discrimination, stigma, and prejudice on the basis of sexual orientation and gender identity negatively impacts sexual minorities 12  www.nature.com/scientificreports/ A previous study showed that Black and Latino same-sex-attracted individuals reported higher rates of depressive symptoms compared to their heterosexual counterparts 13 . However, this study did not evaluate the intersection of sex, race, and sexual orientation with respects to depression. Our data showed that black female sexual minorities had the highest rates of depressive symptoms. To our knowledge, this is one of the few studies that have evaluated the intersection between sex, race, and sexual orientation.
Our study identified that the intersectional group of black, sexual minority, and female sex had the highest level of C-reactive protein compared to other groups. The intersection of social categorizations including sex, race, and sexual orientation result in overlapping, interdependent systems of advantages or disadvantages. In this report, we showed that black female sexual minorities experience overlapping prejudices that may further increase stress levels 14 . On the other hand, other investigators have found that sexual minority men had higher levels of C-reactive protein compared to sexual minority women 15 . Clearly, the role of inflammation warrants further analysis given the multiple biologic and external factors that may confound these results.
Such factors such as sedentary lifestyle, diet, and disordered sleep were not included in our study. Medical illnesses including cancer, autoimmune, inflammatory disorders, and cardiovascular disease are also limited. Additionally, there is much unknown in regard to childhood impact, with factors such as childhood maltreatment and emotional as well as physical trauma.

Conclusion
Female black sexual minorities reported significantly higher depressive symptoms compared to their white heterosexual counterparts. Based on our findings, further studies are warranted to address the reasons behind the disparities in the incidences and treatment of depression in correlation with systemic inflammation biomarkers. Additionally, this study highlights the need for improved social support systems and clinical mental health treatment for these at-risk subgroups. www.nature.com/scientificreports/