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Introduction The prevalence of autism spectrum disorder (ASD), characterized by difficulties in socialization, communication and restricted and repetitive interests and behaviors (American Psychiatric Association, 2013), has increased dramatically in recent decades (Elsabbagh et al., 2012). The symptomatology of the disorder and associated behavioral problems are generally associated with some level of disability. This makes it necessary for individuals with ASD to have caregivers to look after them (Ruiz-Robledillo and Moya-Albiol, 2012). Due to the early manifestation of the symptoms of ASD, the caring role is usually assumed by members of the close family, in the majority of cases, the parents (Davis and Carter, 2008; Hastings, 2003; Rivard, Terroux, Parent-Boursier and Mercier, 2014; Ruiz-Robledillo, Antón-Torres, González-Bono and Moya-Albiol, 2012; Schieve, Blumberg, Rice, Visser and Boyle, 2007). Caring for offspring with ASD entails coping with a range of challenges associated, directly or indirectly, with the caring role (Ruiz-Robledillo et al., 2012). This puts caregivers under chronic stress, which could have severe negative consequences for their health (De Andrés-García, Moya-Albiol and González-Bono, 2012; Lovell, Moss and Wetherell, 2012a; Ruiz-Robledillo et al., 2012). Indeed, compared with the general population, informal caregivers of people with ASD have been found to have more somatic symptoms, depression and anxiety and poorer quality of life (Allik, Larsson and Smedje, 2006; De Andrés-García et al., 2012; Ruiz-Robledillo et al., 2012; Singer and Floyd, 2006). Chronic stress exposure has classically been related to serious negative health outcomes in several populations, including individuals with burnout or post-traumatic stress disorder, victims of intimate partner violence, and informal caregivers (Blasco-Ros, Sánchez-Lorente and Martínez, M., 2010; De Andrés-García et al., 2012; Mingote, Moreno and Gálvez, 2004; Sánchez-Lorente, Blasco-Ros and Martínez, 2012; Schnurr and Jankowski, 1999). The biological mechanisms involved in this health deterioration are believed to be alterations in the functioning of various physiological systems, two of the most important being the hypothalamic pituitary adrenal (HPA) axis and the autonomic nervous system (ANS) (Juster, McEwen and Lupien, 2010). The functioning of the HPA axis has mostly been studied by measuring levels of cortisol, a hormone closely related to the stress response and responsible for various biological changes characteristic of this response (Dedovic, Duchesne, Andrews, Engert and Pruessner, 2009; Hellhammer, Wüst and Kudielka, 2009). Cortisol is a glucocorticoid secreted by suprarenal glands with a specific circadian rhythm of secretion, levels peaking at around 30 minutes after awakening (Clow, Hucklebridge, Stalder, Evans and Thorn, 2010). This rapid increase, called the cortisol awakening response (CAR), has shown to be one of the most reliable markers of the functioning of the HPA axis (Chida and Steptoe, 2009). The purpose of this adaptive response is understood to be to produce physiological changes to prepare the individual for coping with the challenges of the coming day, maintaining body homeostasis (Fries, Dettenborn and Kirschbaum, 2009). Analysis of CAR has found it to be influenced by several demographic, physiologic and lifestyle factors, such as age, gender, phase of the menstrual cycle, and smoking, as well as some psychological and psychosocial factors (Chida and Steptoe, 2009; Fries et al., 2009). Further, CAR has been used in previous research as a reliable marker of health status in several populations, including people under high levels of chronic stress (Chida and Steptoe, 2009; Fries et al., 2009). In informal caregivers, results concerning the CAR have been mixed. Some studies have found higher CAR (Wahbeh, Kishiyama, Zajdel and Oken, 2008), while other studies found lower CAR (Bella, García and Spadari-Bratfisch, 2011; Seltzer et al., 2010) or no differences between caregivers and non-caregivers (Lovell et al., 2012a). These discrepancies could be due to factors not analyzed in these studies, including differences in the diagnoses of care recipients, other contextual factors or psychological traits of caregivers. In the case of caregivers of people with ASD, one study found a lower CAR in caregivers (Seltzer et al., 2010) and another no significant differences between caregivers and non-caregivers (Lovell et al., 2012a). However, these studies considered the full autism spectrum and did not consider autism severity of the care recipient. The other main system involved in the stress response is ANS. The markers of its functioning in the context of stress are mainly electrodermal activity (EDA), as a measure of skin conductance response, and cardiovascular indicators. The evaluation of these markers has shown to be useful for understanding the alteration of the functioning of the ANS in chronically stressed populations (Boucsein, 2012; Thayer, Ahs, Fredrikson, Sollers, and Wager, 2012). In informal caregivers, a few studies have evaluated the functioning of the ANS in laboratory settings or in natural situations (Gallagher and Whiteley, 2012; Gonçalves and Graça, 2011; González-Bono, De Andrés-García, Romero-Martínez and Moya-Albiol, 2013; Soares, 2009). In particular, caregivers of people with cancer were found to have a higher electrodermal response to acute stress than non-caregivers (Gonçalves and Graça, 2011), while no differences were found in caregivers of people with drug addiction (Soares, 2009). It is plausible that, as has been found in other biological markers of health, these inconsistent results are related to differences in the diagnosis of care recipient. In any case, no previous studies have been conducted analyzing electrodermal response to laboratory-induced acute stress in samples of caregivers of people with ASD. Protective and risk factors for health Previous research has shown severe health deterioration in informal caregivers of people with ASD, and the majority of studies have identified risk factors. In this regard, psychosocial variables and factors related to the care recipient are the most widely studied factors (Boyd, 2002; Davis and Carter, 2008; Lai and Oei, 2014; Lecavalier, Leone and Wiltz, 2006). Maladaptive coping and lower levels of social support have classically been associated with poorer health outcomes in this population (Boyd, 2002; Lai and Oei, 2014; Lovell, Moss and Wetherell, 2012b), while in relation to the care recipient, high severity of autistic symptomatology and a high frequency of behavioral problems have been directly associated with negative effects on the health status of caregivers (Huang et al., 2014; Lecavalier et al., 2006; Lovell, Moss and Wetherell, 2015; Ruiz-Robledillo et al., 2012). In contrast, there is a lack of studies analyzing protective variables. Specifically, although previous studies have evaluated psychological traits as protective factors against health deterioration in other samples, no previous studies have analyzed these types of variables in informal caregivers of people with ASD. Furthermore, no previous studies have employed biological markers in the evaluation of this type of factors and other contextual dimensions. Recent research points to the importance of resilience for health protection in chronically stressed populations (Rutten et al., 2013). Although there is no consensus on its definition, resilience is related to coping effectively with stress without negative consequences, and to obtaining positive outcomes from stressful situations (Bayat, 2007). This ability has been associated with positive views of stress, successful adaptation to such situations, and protective effects against health deterioration in informal caregivers (Bayat, 2007; Fernández-Lansac and Crespo, 2011). A recent study found a positive association between resilience and adaptive psychological functioning in informal caregivers of people with dementia (Fernández-Lansac, Crespo, Cáceres and Rodríguez-Poyo, 2012). In informal caregivers of people with ASD, high resilience has been shown to provide caregivers with effective coping skills for managing stressful situations, and in turn, suffering less negative health outcomes (Bekhet, Johnson, & Zauszniewski, 2012). However, no previous studies have evaluated the effects of resilience on health status in this population employing both self-reported and biological markers of health. Another potential protective factor of health is emotional intelligence (EI). Taking into account the high levels of negative affect that are characteristic of caregivers of people with ASD and the positive association between this type of affect and negative health consequences, it seems important to assess EI in this population (De Andrés-García et al., 2012; Singer and Floyd, 2006). EI is generally defined as the ability to identify and manage negative emotional states, and being able to enhance positive ones (Salovey, Mayer, Goldman, Turvey, & Palfai, 1995). It can be described in terms of three factors: attention, the tendency to pay attention to and think about emotions and feelings; clarity, the ability to understand one’s own emotional states; and repair, the ability to regulate one’s feelings, terminating negative emotions and/or prolonging positive ones (Fernández-Berrocal, Extremera and Ramos, 2004). Although EI has shown to be protective against health deterioration in several samples (Schutte, Malouff, Thorsteinsson, Bhullar, & Rooke, 2007), not all of the components of EI seem to have the same relationship with health outcomes. In particular, attention has been associated with poorer health, in contrast to clarity and repair, which have been related to positive health outcomes (Ciarrochi, Deane & Anderson, 2002; Extremera and Fernández-Berrocal, 2006; Extremera and Fernández-Berrocal, 2002). No previous studies have evaluated the role of EI in the care context, despite it being a variable that is closely related to emotional regulation and could be involved in the reduction of negative affect. Regarding contextual variables, institutional support provided for both caregivers and care recipients has shown to be protective of health in caregivers of people with schizophrenia (González-Bono et al., 2013; González-Bono, De Andrés-García and Moya-Albiol, 2012). In these studies, caregivers without institutional support exhibited a blunted CAR and lower heart rate (HR) response to laboratory-induced stress compared to the responses in those with support. Moreover, care recipients of caregivers with institutional support exhibited high levels of autonomy and lower severity symptoms (González-Bono et al., 2013; Gónzalez-Bono et al., 2012). However, no attempt has been made to replicate these findings in samples of informal caregivers of people with ASD. Psychotherapeutic interventions with informal caregivers Even though health deterioration has been widely demonstrated in caregivers of people with ASD, few studies have analyzed the effects of psychotherapeutic interventions focused on improving health status in this population. Some studies have evaluated the indirect effects on caregiver status of interventions addressing the management of behavioral problems and autistic symptoms of care recipients. Such interventions have been found to have positive effects, reducing stress levels, in the majority of the cases (Drew et al., 2002; Salt et al., 2002; Smith, Groen and Wynn, 2000; Tonge et al., 2006). However, there has been relatively little research into the effects of interventions focused on teaching caregivers stress management skills and improving their health status. A meta-analysis of studies on group interventions in informal caregivers of people with developmental disabilities indicated that interventions based on cognitive-behavioral training reduced perceived stress and psychological dysfunction (Singer, Ethridge and Aldana, 2007). However, these studies did not consider intervention programs developed or adapted for a specific care context and did not evaluate more than one health variable. Regarding new therapeutic approaches, such as mindfulness therapy, several studies have also reported good results family caregivers of people with ASD (Ferraioli and Harris, 2013; Singh et al., 2007; Singh et al., 2006). Specifically, one study demonstrated a positive effect on stress levels after a mindfulness intervention oriented to teaching four parents mindful skills for interacting with their children (Singh et al., 2007). A recent study has also shown positive results in the implementation of a mindfulness-based stress reduction program in this population, with reductions in stress, depression and anxiety (Dykens, Fisher, Taylor, Lambert and Miodrag, 2014). However, no biological markers of health were employed in any of these studies. The main objectives and hypotheses of this Ph.D. work are summarized below: 1. To characterize the health status of a sample of family caregivers of people with Asperger Syndrome (AS) through self-reported health measures and cortisol awakening response (CAR) in comparison with a non-caregiver group. The secondary objective was to identify variables related to care recipients and to psychosocial and psychological traits of caregivers that were predictors of health status in caregivers. It was hypothesized that parents of people with AS would take more medication and have poorer self-reported health than those in the control group (Allik et al., 2006). In addition, it was expected that they would have a lower CAR than controls (Bella et al., 2011; Gonzalez-Bono et al., 2011), although as noted above the results to date on this subject are inconclusive (Lovell et al., 2012a; Wahbeh et al., 2008). It was also expected that lower levels of social support, a greater use of maladaptive coping, and higher levels of negative affect and burden would be associated with poorer health in caregivers (Hastings et al., 2005; Khanna et al., 2011). Finally, it was hypothesized that caregivers with higher levels of resilience and EI would show fewer symptoms. 2. To investigate the association between resilience and health markers (both self-reported health and CAR) in family caregivers of people with ASD. The secondary objective was to identify possible associations between resilience, health and social support in this population. It was expected that highly resilient caregivers would have better perceived general health and lower morning cortisol levels (Cicchetti & Rogosch, 2007; Fernández-Lansac et al., 2012). Although no previous studies have analyzed the mediating role of social support in the association between resilience and health, it was hypothesized that social support would mediate this association. 3. To investigate the association between components of EI (attention, clarity and repair) and health markers (both self-reported health and CAR) in family caregivers of people with ASD. The secondary objective was to assess whether CAR was a mediator between EI and self-reported health. Overall, self-reported health was expected to be associated negatively with attention and positively with clarity and repair (Ciarrochi et al., 2002; Extremera & Fernandez-Berrocal, 2006). Though there were no previous data on this in caregivers, it was hypothesized that an altered HPA axis response would mediate the relationship between EI and caregivers’ health, as suggested in a previous study conducted with students (Mikolajczak, Roy, Luminet, Fillée and Timary, 2007). 4. To contrast health complaints in groups of caregivers of people with high-functioning autism (HFA) who were and were not receiving institutional support, and a non-caregiver group, evaluating both self-reported health and CAR. The secondary objective was to explore variables that could modulate the effectiveness of institutional support in protecting the health of caregivers, considering burden and factors related to the functional status of the care recipient, such as dependence and autistic symptomatology. It was hypothesized that non-supported caregivers would present more somatic symptoms and an altered CAR when compared to supported caregivers and non-caregivers (Allik et al., 2006; Tonge et al., 2006). Further, non-supported caregivers were expected to show higher levels of burden than supported caregivers (Salt et al., 2002). In addition, care recipients of non-supported caregivers were expected to show more severe autistic symptoms and higher levels of dependency than the offspring of supported caregivers. Finally, it was hypothesized that higher functional status and less severe symptoms in care recipients and lower levels of caregiver burden would be associated with higher CAR in caregivers (Seltzer et al., 2010). 5. To compare the stress response to a laboratory cognitive stressor in informal caregivers of people with ASD and non-caregivers through the analysis of EDA. The secondary objectives were to compare self-reported health and negative affect between caregivers and non-caregivers, and to analyze the association between electrodermal response, self-reported health and psychological responses to stress. Despite the lack of conclusive evidence from previous studies in caregivers, caregivers were expected to have lower electrodermal and higher psychological responses than non-caregivers, due to the high levels of negative affect in the former (Miquel, Fuentes, García-Merita and Rojo, 1999; Naveteur, Buisine and Gruzelier, 2005; Patrick 2008). In the light of previous research, it was expected that higher scores in anxiety, anger, and negative mood state responses would be related to lower EDA in both groups (Carrillo et al. 2001). Further, taking into account the previous research in this field, rates of somatic symptoms were expected to be higher in participants with higher electrodermal response (Papousek, Schulter and Premsberger, 2002). 6. To analyze the effects of a mindfulness-based program (MBP) on mood state and health complaints through the use of self-reported measures and biological markers of stress, namely, afternoon cortisol levels and cortisol awakening response (CAR), in a sample of parents of individuals with ASD (caregivers) and parents of typically developing children (non-caregivers). The secondary objective was to analyze the efficacy of the program for improving health and negative mood in each group, comparing its impact on caregivers and non-caregivers. It was hypothesized that both caregivers and non-caregivers would show better mood (less anxiety, negative mood, and feelings of anger) (Lykins and Baer 2009), as well as lower afternoon cortisol levels (Lengacher et al. 2012), after each session of MBP. In addition, it was hypothesized that the health status of caregivers and non-caregivers would improve after the intervention program, together with some degree of normalization in morning cortisol levels (Bränström, Kvillemo and Akerstedt, 2013). Finally, it was hypothesized that these improvements in health and mood state would be more pronounced in caregivers than non-caregivers after the program, because caregivers are a chronically stressed population, and the MBP program is primarily focused on stress management. This hypothesis is in line with the results of previous research in which this type of program has been used with caregivers (Lengacher et al. 2012; Minor, Carlson, Mackenzie, Zernicke and Jones, 2006). 7. To assess the effectiveness of a CBT program in reducing burden, somatic symptoms and depression, and improving mood state in informal caregivers of people with ASD. It was hypothesized that caregivers would report a lower level of burden immediately after the intervention and would have fewer somatic and depressive symptoms after the intervention and at 1-month of follow-up (Bristol, Gallagher and Holt, 1993; Hastings and Beck, 2008; Salt et al., 2002). Furthermore, there was expected to be a significant reduction in negative mood states over the course of the whole intervention program. Discussion The findings of this research underline how severely the health status of informal caregivers of people with ASD is affected by their caregiving role, this being reflected in both self-reported and biological markers of health. As hypothesized, informal caregivers were found to have more somatic symptoms and poorer perceived general health than non-caregivers. Furthermore, they had high levels of negative affect and medication use. These results have been reinforced by the evaluation of CAR, a reliable biological marker of health status (Fries, Dettenborn and Kirschbaum, 2009). In contrast to previous studies (Lovell, Moss and Wetherell, 2012; Seltzer et al., 2010), in the present research, informal caregivers of people with ASD were found to have a higher CAR than non-caregivers. As has been proposed, these differences could be due to the anticipation of care demands by caregivers. The anticipation hypothesis was put forward in the work of Schulz, Kirschbaum, Prüßner, and Hellhammer (1998) in relation to individuals chronically stressed by work overload. In that research, the CAR was higher in chronically stressed than non-stressed individuals. Further research evaluating CAR on weekdays and at weekends in similar populations replicated these results, and the authors associated a higher CAR with the anticipation of upcoming demands (Schlotz, Hellhammer, Schulz and Stone, 2004). Recent research conducted in the general population has also demonstrated the effects of anticipated challenge on CAR (Wetherell, Lovell and Smith, 2014). Specifically, the CAR of individuals was evaluated on a normal day and on a day on which they were to be subjected to a laboratory stressor, and CAR was found to be higher on the day of the anticipated laboratory stressor than the normal day. Taking into account that caregivers should cope every day with several demands associated with care context, such anticipation could be a common and chronic condition in this population. This may explain, in part, the higher CAR that has been obtained in two consecutive days in this population. In this sense, it has been proposed that CAR is closely related to awakening processes, fundamentally to the activation of memory representation, about self and orientation in time and space (Fries et al., 2009). In this regard, structures related to memory processes, such as the hippocampus, directly influence the HPA axis, activating or inhibiting its activity (Fries et al., 2009). The anticipation of upcoming demands could be linked to memory processes and the association between hippocampus and the HPA axis could be the biological mechanism underlying the anticipation hypothesis. In the care context, the higher CAR in caregivers of people with ASD could be a consequence of their representation of the care demands after awakening. As has been found previously, caregivers need to cope every day with a range of challenges associated with the care context, and clearly, they also have to deal with other challenges associated with their daily life. In line with this, higher CAR could be an adaptive change in order to increase physiological resources to face these daily challenges. However, high cortisol levels maintained over time could trigger hypercortisolism, severely affecting the health status of the caregiver (Schulz et al., 1998; Lindfors and Lundberg, 2002). On the other hand, as has been observed, perceived stress and demands may be modulated by various psychological trait variables. In particular, both resilience and EI have shown to be associated with health outcomes. As in previous research (Bekhet, Johnson and Zauszniewski et al., 2012), resilient coping was found to be a protective factor against negative health outcomes in caregivers. Highly resilient caregivers presented better perceived general health and lower morning cortisol levels than caregivers with lower resilience levels. In relation to this, previous research has demonstrated that highly resilient individuals have a greater ability to cope with stressful situations, minimizing alterations in the functioning of the HPA axis (Ozbay et al., 2007). It seems likely that, compared to caregivers with a low level of resilience, highly resilient caregivers perceive care demands to be less burdensome, as a consequence of their more adaptive coping resources. This fact could be closely related to their lower levels of morning cortisol levels, a possible biological mechanism underlying their better health status. Furthermore, resilience was closely related to social support, demonstrating that the two variables could interact in providing protection against health deterioration in this population (Boyd, 2002). As with resilience, EI showed a significant association with CAR and self-reported health in caregivers. However, depending on the component of EI considered, different relationships were found. Attention to feelings was associated with more symptoms and poorer self-perceived general health. Greater attention to feelings could enhance rumination processes and this might be characteristic of neurotic personalities, both constructs classically related to negative health consequences (Sansone and Sansone, 2012). Due to the higher prevalence of negative affect in the informal care context, constantly paying attention to one’s own emotions could reinforce and magnify this negative emotionality in caregivers. In contrast, high clarity and repair could allow caregivers to identify and adequately manage negative emotional states, with an adaptive continuum from the perception of feelings, to their identification and regulation. Such abilities could decrease the negative affect in caregivers. In line with this, clarity and repair were associated with lower morning cortisol levels in the present research. Taking into account that negative affect has been related to higher CAR (Polk, Cohen, Doyle, Skoner and Kirschbaum, 2005), it is probable that caregivers with higher clarity and repair abilities had lower negative affect and, in line with this, lower morning cortisol levels. Such a pattern could also explain the better self-reported health in caregivers with high clarity and repair and lower attention to feelings. Furthermore, as proposed in the case of resilience, caregivers with lower attention and higher clarity and repair could have better emotional regulation abilities, coping in an adaptive manner with the stress associated with the care situation and perceiving the level of care demands to be less burdensome. This could also explain the lower CAR in caregivers with the aforementioned pattern of EI. Given that both resilience and EI are protective variables that promote adaptive coping stress abilities, and based on the obtained results, it is probably that those caregivers with higher resilience and greater clarity and emotional repair perceive the care demands as less stressful. Therefore, this perception could be related to an adaptive anticipation of care demands, regulating the HPA axis activity, maintaining it in an optimal functioning. When other contextual factors were studied, institutional support was also found to be a significant protective factor of health in this population, as observed previously in caregivers of people with schizophrenia (González-Bono, De Andrés-García, Romero-Martínez and Moya-Albiol, 2013; González-Bono, De Andrés-García and Moya-Albiol, 2012). Caregivers with institutional support exhibited better health status and lower burden than caregivers without support. Furthermore, the former showed a normal CAR, unlike caregivers without support, who presented a blunted CAR. In this regard, the multidimensional treatment approach applied with caregivers in this research, demonstrated efficacy in both caregivers and care recipients. It has previously been found that this type of intervention is more effective than single types of treatment applied alone (Singer, Ethridge and Aldana, 2007). However, no studies had evaluated new treatment approaches, such as mindfulness interventions, which have shown to be effective reducing perceived stress and negative mood in caregivers of children with chronic conditions (Minor, Carlson, Mackenzie, Zernicke and Jones, 2008). In the present work, the mindfulness-based program developed showed a significant efficacy in reducing somatic symptoms and depression while improving perceived general health in caregivers. Furthermore, as had been hypothesized, caregivers who participated in the intervention presented lower negative mood after the intervention than at the baseline. These results were reinforced by the findings concerning their cortisol response to the sessions. Specifically, caregivers experienced a significant reduction in cortisol levels over the course of the sessions, demonstrating the positive effect on the HPA axis of the meditation and exercises conducted during the intervention program. Furthermore, caregivers showed greater reductions in cortisol levels, negative mood and health complaints than non-caregivers. This result is especially important in terms of demonstrating the potential value of this intervention for chronically stressed populations. In relation to this, training caregivers in the principles of mindfulness, such as living in the present moment with non-judgmental acceptance, could be directly associated with the improvement of health status (Oken et al., 2010). Taking into account that worries about the future of the care recipient, rumination processes and negative affect could be precursors of stress and health deterioration in this population, teaching caregivers new coping skills for dealing with these factors could be particularly effective. Like the mindfulness intervention, a CBT program adapted to the care context was found to be effective for reducing health problems and negative mood in caregivers of people with ASD. In this intervention, sessions were oriented to teach caregivers specific coping skills to deal with the stress derived from the care situation. Accordingly, caregivers could be expected to strengthen their resilience and emotional regulation abilities, both variables that have demonstrated to be protective against health deterioration in this population. Although the efficacy of the mindfulness and CBT-based approaches could be due to different mechanisms, both were oriented to provide caregivers with effective coping skills to deal with the stress in an adaptive manner. This focus seems to be successful for reducing health complaints, increasing perceived quality of life in caregivers. Regarding the functioning of the ANS, experiments were conducted to evaluate the electrodermal response to acute cognitive stressors in the laboratory setting. Caregivers had a lower electrodermal response to acute stress than non-caregivers. As has been found in other chronically stressed populations, a habituation mechanism could explain these results (Gump and Mathews, 1999). In samples of abused children or individuals with a background of severe poverty, the response of the ANS to acute stress was observed to be blunted (Evans and Kim, 2007; Murali and Chen, 2005). Being under high levels of chronic stress could affect the functioning of the ANS, making this system hypo-responsive due to habituation mechanisms (Carroll, Phillips, Ring, Der and Hunt, 2005; Evans and Kim, 2007; Murali and Chen, 2005). In this regard, when the acute stress response has been studied in this population with other biological markers, the results were the same (De Andrés-García, Moya-Albiol and González-Bono, 2012). Caregivers also exhibited lower cortisol response to acute stress than non-caregivers when the same stress protocol was applied, demonstrating that there may also be a habituation to stress in the case of the HPA axis (De Andrés-García et al., 2012). Taken together, these findings imply that the adaptive stress response may be weakened in caregivers, and this could have severe consequences for their health when dealing with several daily stressors. Alternative explanations are based on the effects of chronic stress enhancing adaptive coping and resilience for dealing with the stressor in caregivers (Gump and Mathews, 1999). It is plausible that caregivers develop stronger adaptive coping strategies, and this could reduce their need for greater physiological resources to cope with the stress, protecting their health status. This hypothesis would be consistent with the association observed between self-reported health and EDA, a lower electrodermal response being protective of health. The main limitation of this research is that the design of the study is cross-sectional and correlational, something characteristic of field studies in general and those carried out in this populations in particular, which means that causality could not be addressed. Furthermore, the relatively small sample sizes in some of the studies may limit the generalization of the results in some cases. However, the situation of caregivers makes it extremely difficult to establish studies with larger samples, due to the lack of time and commitments of this population. Along with this, employing biological samples, the number of participants is appropriate, given the complexity in the obtention and determination of the samples. The findings presented in this Doctoral Thesis represent a significant advance in our understanding of the consequences for health of caring for offspring with ASD. The multidimensional approach in analysis of the health of caregivers, employing both biological and self-reported measures, makes it possible to assess their status in a comprehensive way. This approach enhances the reliability of the results obtained and provides relevant information about the biological mechanisms that could underlie the impact on health of caring for an individual with ASD. Furthermore, the identification of protective as well as risk factors is important to guide the development of assessment protocols including related variables. Such assessments could provide essential information to clinicians about caregivers at risk of severe health impairment. Identifying groups of caregivers at a high risk could make it possible to prevent future health problems, by offering psychotherapeutic interventions. Further, the results obtained could also be useful to inform the development of such interventions for reducing health problems and stress perception in this population. As demonstrated, two types of intervention focused on stress management are useful for reducing health complaints, including techniques and exercises oriented to enhancing factors found to be protective of health and reducing the risk factors. Future studies should consider other biological markers of health, and other psychological traits of caregivers that could be involved in the impact of caring on their health. In addition, as a lack of time is characteristic of informal caregivers, the efficacy of other modalities of intervention based on new technologies should be analyzed, for instance, telehealth approaches. Such innovative approaches could avoid one of the main barriers to treatment adherence in this population, taking into account that this type of imntervention could be performed in their own homes with the help and guidance of professionals via Internet. Furthermore, future research should analyze the differential efficacy of diverse types of treatments or their combination, in order to establish effective intervention protocols for this population. 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