3.1: Focus on the individual 
In terms of  individual factors contributing to health and wellbeing, our original GENIAL framework highlighted the critical role of positive psychological experiences as well as positive health behaviours. We use the term ‘psychological experiences’ to refer to an individual’s interpretation of life events and the temporal narrative relating to the events over one’s life course via cognitive and emotional processes. Although there is a wealth of evidence demonstrating a reciprocal relationship between health behaviours and psychological experiences, reviews on one typically do not discuss the other. There are two potential reasons for this: 1) the distinction between mind and body remains an issue of great philosophical debate, with consequences for mental and physical health, and, 2) researchers tend to work in disciplinary silos, a phenomenon reinforced by higher education, focused research areas and targeted funding initiatives. In this section we discuss both positive psychological experiences and positive health behaviours, laying the foundation for improving individual wellbeing with an eye towards applying this information to improving wellbeing in people living with chronic conditions in future research. 

Psychological experience   

Major theories relating to the wellbeing of individuals (Table \ref{348217}) can be categorised according to two contrasting philosophical positions: hedonic and eudaimonic wellbeing. According to the hedonic standpoint, wellbeing is achieved by focusing on pleasurable experiences in order to enhance positive affect. A major theory is the 'tripartite model of subjective wellbeing', proposed by \cite{Diener_1984}, highlighting a role for life satisfaction, decreases in negative affect and increases in positive affect. Another key model is the 'broaden and build' theory by Barbara Fredrickson \cite{Fredrickson_2001}, which emphasises a role for positive emotions such as joy, interest, contentment, pride and love in broadening individual thought-action tendencies that subsequently build personal resources for individual growth, social connection and psychological resilience. Research has shown that positive emotions increase the perception of social connectedness, enhance vagal function, and facilitate the adoption of positive health behaviours, among other factors \citep{Kok2010,Sin2015,Kok2013}. Recent longitudinal research \cite{Petrie_2018} observed that participants in a low positive affect grouping have a twofold increased risk for mortality, compared to those in the more favourable grouping over a 16.5 year follow-up period. Positive affect has been shown to affect health via inflammation, such that greater trait positive affect is associated with reduced pro-inflammatory cytokines \citep{Stellar2015}. Interested readers are also referred to major reviews on this topic \cite{Chida_2008,DuBois_2012,Boehm_2012}. Our own work emphasises the role of vagal function over these allostatic systems \cite{Kemp_2017,Kemp2017,ah2018,Kemp_2013,Kemp_2016a}.
In contrast to a focus on hedonia, eudaimonic theories of wellbeing look beyond momentary happiness, focusing on purpose, meaning in life, and flourishing. According to this perspective, Carol Ryff’s Psychological Wellbeing theory \citep{Ryff_1995,Ryff_2014,Ryff_1989} emphasises six elements that contribute to psychological wellbeing including self-acceptance, personal growth, purpose in life, positive relations with others, environmental mastery, and autonomy. As with hedonic wellbeing, psychological wellbeing has also been associated with improved health, including subjective health, chronic conditions, symptoms and functional impairment \cite{Ryff_2014}. Purpose in life reduces risk of developing Alzheimer's disease and mild cognitive impairment \citep{Boyle2010} along with reducing risk of death \citep{Boyle2009}. Postmortem results have even revealed that - among those with high levels of brain pathology - those with greater purpose in life presented with better cognitive functioning whilst they were still alive, highlighting a moderating role of purpose in life on the relationship between brain-based pathology and cognitive functioning \citep{Boyle2012}. A more recent study reported that a stronger sense of purpose is associated with decreased mortality \cite{Alimujiang_2019}, an effect associated with a hazard ratio of 2.43 (95% CI, 1.57-3.75) when comparing those in the lowest life purpose category with those in the highest life purpose category.
However, these theoretical models - especially those focusing on hedonia - have faced criticism. As alluded to above, the focus on 'happiology' has been criticised as lacking in nuance. Positive affect alone is not sufficient for improving wellbeing and over-valuing the need to be happy can actually lead one to feel less happy \cite{Mauss_2011}, and may even be associated with the symptoms and diagnosis of unipolar depression \cite{Ford_2014} and bipolar depression \cite{Ford_2015}. Other writers have criticised the individualistic focus, which ignores the impact of community and wider environmental factors \cite{davies2015,Frawley_2015,Carlisle_2009}. Eudaimonic theories have also attracted criticism for not recognising the importance of positive emotions, leading to proposals such as Seligman's PERMA model \cite{seligman2011,Seligman_2018}, which incorporates aspects of both hedonic and eudaimonic theory. The PERMA model argues for a five-pronged model of wellbeing including positive emotions, engagement, positive relationships, meaning, and accomplishment (i.e. PERMA). According to this model, all five pillars of wellbeing contribute to flourishing in life. While theories relate to concepts of hedonia and eudaimonia as well as their combination, recent research has shown a large overlap between them. For instance, research by Todd Kashdan and colleagues \citep{Disabato_2016} reported a high latent correlation of .96 between Diener's subjective wellbeing model of hedonia \cite{Diener_1984} and Ryff's psychological wellbeing model of eudaimonia \cite{Ryff_1989} indicating that the discriminant validity of these constructs is negligible. Critically, analyses across seven geographical world regions revealed similar results. The authors however, noted three exceptions to this trend, which were 'hope', 'meaning orientation' and 'grit', which differentially related to hedonia and eudaimonia, giving some support to the discriminant validity of the two constructs. In another study by the same authors \cite{Goodman_2017}, PERMA was observed to measure the same type of wellbeing as Diener's model of subjective wellbeing with confirmatory factor analysis yielding a latent correlation as high as .98. The authors subsequently criticised PERMA for not offering any further insights into wellbeing beyond the former theory of SWB. In response to this, Seligman has argued that PERMA is not "redundant" simply because different models correlate; instead, PERMA presents a model that constitutes the critical elements of wellbeing \cite{Seligman_2018} and one what that we draw and build on in our own applied research (see section \ref{223145}). 
Building on strong theoretical foundations and an extensive body of research, our previously published models \cite{Kemp_2017a,Kemp_2017} argue that healthy vagal nerve function, underpin and are impacted on by positive psychological moments, facilitating longer-term improvements in health and wellbeing. These insights are based on a strong body of evidence. For instance, Todd Kashdan and Jonathan Rotenberg \citep*{Kashdan_2010} argued that vagal function is an index of psychological flexibility (PF) that is fundamental for psychological health. Psychological flexibility is an important component of resilience, facilitating ones capacity to assess and adapt to demands, alter mindset and behaviour when necessary, and for commitment to behaviours that are congruent with deeply held values \citep*{Kashdan2010}. Conversely, psychological inflexibility has been associated with worsened mental health and an exacerbated stress \citep{Masuda_2011,Kato2016,Chawla2007,White2013,Smeekens2007}. An inflexible response style - characterised by withdrawal of the vagal brake - plays a key role in the development of and symptomatology of depression \citep*{Nolen_Hoeksema_2008}, along with explanatory inflexibility (applying the same attribution style cross different situations) and inflexible coping behaviours \citep{Fresco_2006,Moore2007}. According to \citet*{Kashdan_2010}, vagal function underpins the capacity for psychological flexibility. Intriguingly, Bethany Kok and Barbara Fredrickson \citep{Kok_2010,Kok_2013} demonstrated that change in vagal function - following training in loving kindness meditation - is associated with increases in positive emotions and enhanced perception of social connectedness, suggesting that positive emotions facilitate physical health via the vagus nerve. The link between individual and community is a topic that we turn to following our discussion of positive health behaviours.

Health behaviours 

Whilst health behaviours are typically thought of with respect to their impact on physical health, there is now compelling evidence that health behaviours impact on both physical and mental health. Accordingly, and in contrast to many other models of wellbeing \cite{Ryff_1989,Diener_1984,seligman2011a}, we have proposed a key role for health behaviours in facilitating individual pathways to health, wellbeing and longevity \citep*{Kemp_2017}. Moreover, we propose the vagal nerve acts as the structural link between physical and mental health and plays a critical role in reciprocal relationship between positive health behaviours, and physical and mental health. In this section, we present some key studies highlighting the importance of health behaviours in physical and mental health outcomes. An exhaustive review is beyond the scope of this paper however, and interested readers are referred to \citet*{Kemp_2017}. Given the number of health behaviours, for brevity, we focus specifically on physical activity, diet and sleep.  
Impact of health behaviours on physical health:
A summary of public health guidelines and associated evidence-base relating to physical activity, diet and sleep is provided in Table 2.