Methods

Participants and procedure

Initially, the sample consisted of 467 participants who responded to an online survey, but only 401 fulfilled the inclusion criteria (136 men and 265 women). We excluded participants who were less than 18 years old, participants who had not had sex in the last four weeks, and who were not in a romantic relationship. Descriptive statistics are presented in Table 1. The survey in Portuguese language was advertised in social networking sites (Instagram; Facebook; WhatsApp) from 22 October 2020 to 25 November 2020. After clicking on the survey link, potential participants were presented with the informed consent disclosure that explained that the objectives of the investigation were to study the relationships between mood and sexual functioning, and that the data are anonymous and confidential. It was further stated that the study was aimed at heterosexual and sexually active adults (more than 18 years old). The study was approved by the local Ethics Committee.

Measures

Female sexual function was assessed by a Portuguese version (^{Pechorro et al., 2009}) of the Female Sexual Function Index (^{Rosen et al., 2000}), which has 19 questions clustering in six dimensions: desire, arousal, lubrication, orgasm, satisfaction and pain with higher scores indicating better sexual function. Female sexual distress was measured by a Portuguese version (^{Berenguer et al.,, 2019}) of the Female Sexual Distress Scale - Revised (^{DeRogatis et al., 2008}). This instrument has 13 items measuring several negative emotions related to female sexuality on a 5-point scale with higher scores indicating greater distress with one’s sexuality.

Male sexual function was assessed with the Portuguese version (^{Quinta Gomes & Nobre, 2012}) of the International Index of Erectile Function (^{Rosen et al., 1997}). The Portuguese version of the IIEF has 14 items clustered in the five original five dimensions: erectile function, orgasmic function, sexual desire, intercourse satisfaction and overall satisfaction. Higher scores indicate better sexual function (^{Rosen et al., 1997}).

The quality of the romantic relationship was assessed using the Portuguese short version (^{Costa & Brody, 2007}) of the Perceived Relationship Quality Components Inventory (^{Fletcher et al., 2000}). The questionnaire consists of six items assessing satisfaction, commitment, intimacy, trust, passion, and love on a 7-point scale from 1 (absolutely nothing) to 7 (extremely).

Negative mood was assessed with the Portuguese version (^{Pais-Ribeiro et al., 2004}) of the Depression Anxiety Stress Scale (DASS; ^{Lovibond & Lovibond, 1995}). This instrument has 21 questions (seven items for each dimension rate on a 4-point scale). Each item corresponds to a phrase that refers to negative emotional symptoms and the participants must answer according to how they felt in the last week. The higher the scores in each dimension, the more severe the emotional distress.

Results

In women, better relationship quality correlated with lesser depression (r = -.27; p < .001), lesser anxiety (r = -.19; p = .002), and lesser stress (r = -.20; p = .001). In men, better relationship quality correlated with lesser depression (r = -.41; p < .001), and lesser stress (r = -.24; p = .005), but not with lesser anxiety (r = -.15; p = .073).

As can be seen in Tables 2 and 3, for both sexes, more sexual difficulties correlated with more depression, more anxiety, more stress, and poorer relationship quality.

In order to examine the independent statistical contributions of negative mood and relationship quality in predicting sexual function, while also controlling for the effects of age and use of medicines for depressions or anxiety, we performed a series of multiple regressions, in which the dependent variables were sexual function dimensions, and the independent variables were negative mood (composite measure of depression, anxiety and stress), relationship quality, age, and use of medicines for depression or anxiety. Of note, 12 women (4.5%) reported to consume such medicines, whereas two men (1.5%) reported to do so.

As shown in Table 4, poorer female sexual function was independently predicted by more negative mood and poorer relationships quality across all dimensions with the exception of pain, which was not predicted by relationship quality (in fact, pain was the only dimension of female sexual function that was not associated with relationship quality in univariate correlations, as depicted in Table 2). Interestingly, use of medicines for depression or anxiety was an additional independent predictor of lower desire, more sexual dissatisfaction, and greater sexual distress (see Table 4).

As displayed in Table 5, poorer male sexual function was independently predicted by more negative mood and poorer relationship quality across all dimensions except orgasm, which was unrelated to relationship quality, but nevertheless with a nonsignificant trend.

Discussion

In the present study, we confirmed that, for women and men, more negative mood, poorer relationship quality, and poorer sexual function were intercorrelated, as previous research shows. However, more negative mood and poorer intimate relationship quality were independently associated with more sexual difficulties. Although dysphoria can lead to relationship dissatisfaction, and vice versa (^{Trudel & Goldfarb, 2010}), the two factors appear to influence sexual function by independent means, as the present results suggest. This means that many relationship problems do not affect sexual functioning by means of the dysphoria that can ensue from relationship difficulties. It also means that dysphoric states can affect sexual functioning without affecting the perceived quality of the relationship.

The present findings are important for sex and relationship therapists, as they imply that interventions to improve relationship quality with the aim of improving sex life may not be enough, if mood problems are not addressed. Conversely, ameliorating mood might not be enough to improve sexual function, if relationship quality problems are not addressed. In this regard, it is pertinent to note that relationship quality is a more comprehensive concept than relationship satisfaction by encompassing love, passion, intimacy, commitment, and trust, in addition to satisfaction (^{Fletchers et al., 2000}).

The correlational nature of our findings also implies caution in the interpretation of causal links. Sexual problems may also lead to relationship and mood problems (^{Byers, 2005}; ^{McNulty et al., 2016}; ^{Shiri et al., 2007}), and other variables can additionally play a role in the associations of sexual function with mood and relationship quality; for example, sexual and relationship satisfaction might be improved concurrently by increases in intercourse frequency (^{Brody et al., , 2018}; ^{Weiss & Brody, 2011}), increases in quality of intimate communication (Byers, 2005), as well as by particularly intense experiences during sexual activity (^{Ellero & Costa, 2020}). These are topics to be explored in future research.

It worth noting that, in the present study, use of medicines for depression or anxiety did not influence the relation between negative mood and poorer sexual function; in fact, the use of these drugs independently predicted sexual difficulties. Use of benzodiazepines has been related to sexual dysfunctions (^{Chen et al., 2016}; ^{Ghadirian et al., 1992}), but the research on the topic is yet very limited. It is unclear if sexual dysfunctions emerge from drug effects or are the result of the mental condition for which benzodiazepines are prescribed. Case studies suggest that different benzodiazepines might have different effects on sexual function (^{Balon et al., 1989}), but there is lack of investigation on the subject.

In contrast, it is well known that antidepressants are important causes of sexual dysfunction (^{Lorenz et al., 2016}; ^{Segraves & Balon, 2014}), especially those that increase serotonin neurotransmission (Lorenz et al., 2016; Rothmore, 2020; Segraves & Balon, 2014). Research has been showing that antidepressants (selective serotonin reuptake inhibitors and selective serotonin and norepinephrine reuptake inhibitors) may be more dangerous for sexual function than depression proper (^{Shiri et al., 2007}), and its adverse effects on sexual function may continue after discontinuation (Rothmore, 2020). The role of antidepressants in the aetiology of sexual dysfunctions should be given high consideration, especially when it is becoming increasingly clear that antidepressants do not have clinically significant benefits in comparison with placebos in the treatment of depression and anxiety, regardless of the difference in statistical significance (^{Kirsch, 2014}; 2019; ^{Moncrieff & Kirsch, 2015}). Finally, mood stabilizers also appear to be associated with sexual dysfunction, but research on the topic is scarce (^{La Torre et al., 2014}).

Our findings need to be replicated in more diverse and more representative samples, as our convenience sample consisted mostly of unmarried young people. We need further research in older and/or married samples.

In conclusion, the present study provided evidence that negative mood and poorer relationship quality are independently associated with more sexual difficulties.

Author contributions

Inês Rodrigues: Conceptualization, Data Curation, Formal Analysis, Investigation, Writing - Original draft, Revision and Edition

Rui Miguel Costa: Conceptualization, Data Curation, Formal Analysis, Methodology, Project Administration, Supervision, Writing - Revision and Edition