This relationship is captured by the tagline: 'there is no health without mental health' \cite{Prince_2007}, and our past reviews have emphasised a role for vagal function as a structural link \cite{Kemp_2017,Kemp2017,ah2018,Kemp_2013,Kemp_2016a}.
The global context
Healthcare systems are struggling to meet increasing demand for care due to the increasing burden of NCDs \citep{Guzman-Castillo2017} (Fig \ref{535015}). The treatment gap for mental disorders - referring to the numbers of people who need treatment that are not receiving it - has been estimated to exceed 50% in all countries of the world, and to reach as high as 90% in those with less resources \cite{PATEL_2010}. The treatment lag for mental disorders - referring to the amount of time taken to receive mental health treatment when it does exist - has been estimated to be longer than a decade \cite{Wang_2004}. Part of the problem here is that healthcare systems remain driven by the medical model, which focuses on returning patients to good health (cure), rather than condition management.
These considerations have major societal and economic implications for improving wellbeing of current and future generations.
INTEGRATE THE FOLLOWING [FROM PSYCHOLOGICAL EXPERIENCE SUB-SECTION). THIS INFO SHOULD GO INTO THE GLOBAL CONTEXT. INFO NEEDS TO BE INTEGRATED AND CONTENT REDUCED:
For example, in a study of 245,404 participants from 60 countries across the world, an average of between 9.3-23% of participants with one or more chronic physical condition had co-morbid depression (Moussavi et al., 2007). This is significantly higher than depression rates in people without a chronic physical disease (p>0.0001). Moreover, even after adjustment for health conditions and socioeconomic factors, depression had the largest effect on worsening mean health scores. The authors conclude that participants with one or more chronic condition and co-morbid depression had the poorest health of all of the disease states. Cardiovascular disease, type 2 diabetes mellitus, cancer and chronic respiratory diseases are often referred to as the ‘big four’ chronic conditions, because in combination, they account for more deaths than any other. However, if one considers the global burden of chronic conditions in terms of disability rather than mortality, major depression is the second leading cause of disability (O’neil, Jacka, Quirk, Cocker and Taylor and Berk, 2015) preceded only by cardiovascular disease. In terms of disability, ‘the big four’ only account for only (54%) of all related disability adjusted life years (DALYs). Although, relative to physical health conditions, mental disorders are associated with greater disability, they are much less likely to receive treatment and this holds true across the world (Von Korff MR, Scott KM, Gureje, 2009).
Prevalence rates for major depression are higher for people with physical illness relative to those without. For example, 29% for people with hypotension, 22% for people with myocardial infarction, 33% for people with cancer and 27% for people with diabetes (World Health Organization, 2003).[zf3] The World Mental Health Survey showed odds ratios across countries for the relationship between heart disease and mental health conditions were; 2:1 for depression; 2:2 for anxiety; and 1.4 for alcohol dependence. The relationship between heart disease and mental health conditions (the two biggest contributors to the global economic burden of chronic disease) appears to be reciprocal. For example, major depression has been shown to increase the risk of the development of cardiovascular disease (Gasse, Laursen, Baune, 2014). For example, strong relationships have been reported between early onset common mental health disorders and heart disease in adulthood (Gasse, Laursen, Baune, 2014). Conversely, having a physical illness is one of the strongest predictors of depression (O’Neil et al. 2015; Wilhelm K, Mitchell P, Slade T, 2003). In their meta-analysis, Roest, Martens, DeJonge, Denollet (2010) revealed anxiety disorders also increase the risk for cardio-vascular disease and cardiac related death. The relationship between mental health conditions and chronic conditions remains strong across a plethora of chronic conditions. For instance, type 2 diabetes mellitus, has been shown to increase the risk for depression (Rotella and Mannucci, 2013), anxiety (Wandell, Ljunggren, Wahlström, Carlsson, 2014) as well as schizophrenia, bipolar disorder and post-traumatic stress disorder. Meta-analyses have also shown a strong relationship between diabetes and cognitive impairment (Vancampfort D, Correll CU, Galling B, et al, 2016). Respiratory diseases and cancer have been linked with depression (Caruso R, GiuliaNanni M, Riba MB, Sabato S, Grassi, 2017). In the World Mental Health Survey, mood, anxiety, and substance dependency were shown to preceded a diagnosis of asthma (Scott, Lim, Al-Hamzawi, 2015). These common mood disorders appear to share an underlying diathesis whereby mechanisms that predispose individuals to depression and anxiety for example, contribute to the development of a range of chronic physical health conditions across the life span. A greater understanding of this common underpinning diathesis is needed to better develop preventive interventions and well as treatments. Our original GENIAl model lays the foundations from which these underpinning mechanisms can be better understood (Kemp et a al. 2017).
What is clear, is that interventions that fail to appreciate the role the causal role of psychological experience in physical and mental health as well as the reciprocal relationship between physical and mental health miss substantial opportunities in the prevention and the amelioration of chronic conditions. Moreover, the biases in treatment towards physical illness in the health service is inefficient given that high degree of co-morbidity with mental health conditions because we know that mental ill health affects adherence to treatments and prognosis. DiMatteo, Leeper and Croghan (2000) showed that people with depression were three times less likely to adhere to treatment regimens that people without depression. This commissioning bias also ignores the evidence that health-related quality of life is significantly lower for depressed patients than for people with physical health conditions for example, asthma, arthritis, and diabetes [Moussavi S, Chatterji S, Verdes E, Tandon A, Patel V, et al. (2007)]