Whereas an extensive body of research has highlighted the positive mental health outcomes associated with mindfulness in the general population [31, 32], little research has been conducted to investigate mental health in the specific context of emergency work . However, mindfulness is considered to be a crucial psychological resource for coping effectively with stress and trauma . Thus, it could potentially represent a modifiable protective factor for the mental health of first responders regularly exposed to chronic and traumatic stressors [20, 21]. In light of these ideas, the aim of the present study was to examine the potential relationships between dispositional mindfulness and mental health in a sample of Australian fire fighters who had been exposed to at least one traumatic incident involving death or serious injury over the last 6 months.
It was specifically hypothesised that higher levels of mindfulness would predict lower levels of anxiety and depression as well as higher levels of psychological well-being, controlling for age and years worked within FRNSW. Results indicated strong evidence in support of this hypothesis. As expected, there was a significant positive association between dispositional mindfulness and well-being coupled with a significant inverse correlation between dispositional mindfulness and reported indices of anxiety and depression. Greater mindfulness was associated with higher levels of psychological well-being as well as lower depression and anxiety symptoms within the sample of fire fighters. In addition, the reported relationships were robust across indicators of mental health with mindfulness explaining a substantial amount of the variability in well-being (26.8%), anxiety (23.6%) and depression (22.4%). However, the demographic variables of age and years worked in FRNSW did not affect the influence of mindfulness on any of the mental health outcomes in our sample.
Present findings replicated previous results linking higher levels of mindfulness to enhanced mental health outcomes, including decreased anxiety, depression [17, 31], general psychopathological symptoms , higher psychological well-being  and positive affect . The current findings are also consistent with emerging studies conducted with various groups of first responders [20, 34].
Our regression analyses also demonstrated that age and years of service in FRNSW were not predictive for any of the mental health outcomes considered. Neither of these two demographic variables were significantly associated with psychological indices of anxiety, depression or well-being. Such results are partially consistent with the study of Setti and Argentero, where age was not related to mental health but years of fire service was positively correlated with reported post-traumatic symptoms . However, the discrepant pattern of terms of years of fire service is surprising, particularly in light of studies showing a clear link between overall cumulative trauma exposure and a range of mental health outcomes . This result may be partly explained by the fact that the fire fighters involved in the present study were on average almost 5 years older and had more work experience than the Italian fire fighters in the Setti and Argentero study . It may be that length of service, and therefore cumulative trauma exposure, becomes less of a predictor in more experienced first responders, when almost all have had sufficient trauma exposure to precipitate mental distress. Indeed, a recent study determined that any positive correlations between mental disorder and years of service in first responder organisations was only present among staff who were early in their career .
The finding that mindfulness benefited the mental health of fire fighters exposed to trauma is congruent with prior research emphasising the importance of self-regulation as a key protective function of mindfulness . Being more aware and accepting of the present moment without judgment may facilitate healthy self-regulation processes as evidenced in correlational research demonstrating the link between higher mindfulness and greater awareness, understanding and attentional capacities as well as increased emotion regulation [13, 35].
In this regard, research has demonstrated that mindfulness could exert its beneficial effects through enhancing self-regulation skills essential to adaptive psychological functioning, including an improved ability to control ruminative thinking  as well as negative bias and automatic emotional responses to threat via the insula and amygdala . These findings are in line with prior studies demonstrating that adopting an attitude of acceptance may be beneficial for buffering distress . Indeed, non-reactivity to emotional stimuli could be considered as the operationalisation of acceptance, a crucial dimension of mindfulness reflecting the non-evaluative stance towards the present experience . Adopting an accepting and mindful attitude may foster the capacity to refrain from engaging in impulsive reactions, which has been related to decreased anxiety and depression and increased psychological well-being [17, 37].
Furthermore, present results are consistent with literature suggesting that dispositional mindfulness may be particularly protective for emergency workers who deal with regular trauma exposure . In line with these assumptions, cross-sectional research has previously found that negative relationships between depression and mindfulness were stronger among individuals exposed to high levels of stress compared to those under less stressful conditions . According to Follette et al., mindfulness skills may foster adjustment following traumatic experience through an enhanced processing and integration of trauma-related information as well as a decreased usage of maladaptive avoidant strategies such as withdrawal or substance abuse . While our study was limited to fire fighters who had been exposed to trauma, information about how distressed they felt during the traumatic exposure was not collected. Future research could aim to explore the importance of perceived stress in direct relation to any traumatic event. This could help determine whether the potential protective function of mindfulness in mental health varies according to amount of stress experienced.
Whilst mindfulness, at varying levels, is a trait naturally occurring among humans, research shows that the capacity for mindfulness can be trained with practice [13, 38, 39]. Mindfulness principles have been successfully incorporated in a range of programs aimed at enhancing the psychological well-being of various clinical and non-clinical populations [31, 40]. Current results provide some support for the relevance of considering mindfulness interventions amongst first responders. However, this is an assertion that requires separate testing with intervention studies as it cannot be assumed that trained mindfulness skills will have the same protective effect as dispositional mindfulness.
Although our results suggest that mindfulness could account for about a quarter of the variance of anxiety, depression and well-being amongst first responders, the majority of the variance remains unexplained. Social support has been found to be an important protective factor against the development of psychopathology in adults confronted with traumatic stressors . Consistent with this research, Smith et al. determined that social support was related to reduced depressive symptoms in fire fighters after controlling for mindfulness . Our results are likely to contain unmeasured residual confounding from factors such as social support. Future study may benefit from including social support, as well as other determinants of resilience, in hierarchical regression models to clarify the potential role of mindfulness in the mental health and well-being of first responders.
While this study brings an important contribution to literature on mindfulness and mental health in first responders, there are several limitations. Firstly, the present investigation used self-report questionnaires to assess mental health and mindfulness in fire fighters. Mindfulness may not be fully assessable using self-report due to self-report bias. It may, therefore, be desirable to replicate this study using clinical diagnostic interviews or biomarkers, such as cortisol sampling, to measure psychopathological symptoms of anxiety and depression as well as well-being . The employed scales, however, showed good psychometric qualities and are widely used in research [12, 25, 28, 41]. Secondly, the cross-sectional design of the present study limits the ability to make inferences regarding the direction of causation in the relationship between the observed variables and their underlying constructs. In particular, the possibility remains that some or all of the association between mindfulness and mental health variables is due to the onset of mental health symptoms or poor wellbeing making it more difficult for individuals to utilise mindful techniques. However, research suggests that teaching mindfulness clinically may only be problematic for a minority of trauma survivors with severe symptoms and individuals suffering from severe depression . Thirdly, there may be a problem of multicollinearity in some of the models presented, most notably between age and years of service within FRNSW, which were found to be strongly correlated (r = .74). However, Field  has suggested that only correlation values greater than .80 could jeopardise the validity of the regression model estimates. In order to confirm that the level of correlation between these two variables was not influencing our results, sensitivity analyses were conducted, in which each of the regression models were reconstructed, but only controlling for years worked with FRNSW. As demonstrated in Additional file 1, the overall conclusion remained unchanged. Finally, the fire fighters involved in the study may not be thoroughly representative of fire fighters located in other geographical regions. In particular, our sample had an overwhelming majority of males, meaning we were not able to explore gender differences with any statistical power and remain unsure if these findings are relevant for female workers. Findings would need to be replicated in various emergency groups in different environments and contexts.