Salwa Sayeed & Damindri Fernando
The World Health Organization (WHO) defines mental health as a state of well-being which allows an individual to work and contribute meaningfully to their community whilst coping with the normal stresses of life. Mental illness, on the other hand, is defined as disorders characterised by combinations of abnormal behaviour, thoughts, emotions and interpersonal relationships. Mental illness currently carries an immense global burden of disease, estimated to contribute 32.4% of years lived with disability (YLD) and 13.0% of disability-adjusted life-years (DALYs). This places mental illness as an indisputable, global first by years of life lost (YLL) and on par with cardiovascular disease burden by DALYs.
Notably, in low to middle-income countries (LMIC) with a gross national income (GNI) per capita of <$12,236 , the WHO estimates depressive disorders to be the second leading cause of years lived with disability. Schizophrenia, bipolar disorder, alcohol use disorder and anxiety disorders are also in the top 10 causes of disability due to health-related conditions in LMIC. Strikingly, 80% of sufferers of mental illness reside in LMIC.
Whilst the relationship between poverty and mental illness in industrialised nations has been well-established, the same correlation in LMIC is yet to be established by the literature. This is due to the following reasons: 1. The impact of third factor variables interacting with poverty and mental health, including barriers to mental health services, 2. The way poverty and mental health cyclically cause and impact one-another, 3. Controversy surrounding the best instrument to measure poverty, 4. Lack of research in the area.
Nonetheless, an understanding of poverty as a mental health determinant in these regions is valuable for its ability to inform and direct global mental health policies and interventions. If a causal link between poverty and mental health is established, then there would be health benefits in reducing income inequality. However if such a relationship is disproved, resources could be re-directed into changing health knowledge, preferences and behaviour. This review aims to summarise the literature on whether a causal link between poverty and mental illness can be drawn and thus provide direction for future areas of research in this field.
As the literature on poverty and mental illnesses is primarily on common mental disorders, this review focuses on the same. Regarding definitions of poverty, there are various parameters that can be used including: consumption poverty, highest level of education attained, yearly income, food insecurity and financial stress. As each study cited uses its own measurements, this review does not provide an overarching definition of poverty.
In the interface between poverty and mental health, two main theories have been proposed. Firstly, the ‘social causation theory’ highlights that poverty is a risk factor for mental illness through various mechanisms of social exclusion, stress, deprivation, malnutrition, increased obstetrics risk, violence and trauma. On the other hand, the ‘social drift (or social selection) theory’ suggests vice versa, that mental illness can cause impoverished conditions through low employment, low productivity and stigma. Nevertheless, it is likely that both pathways are at play in mental illness.
Poverty and mental illness
A 2003 article by Patel and Kleinman et al. reviewed the association between poverty and common mental health disorders in six LMIC through English-language journals and global mental health reports published since 1990. Most studies showed a robust association between poverty and common mental disorders, particularly asserting that they interact in a vicious cycle. The most strongly associated measure of poverty was low levels of education. The contribution of low level education to increasing hopelessness, insecurity, rapid social change and limited opportunities ultimately increases mental illness development risk. Contrastingly, actual income was less implicated as a risk. However, the article did not find causal associations between poverty measurements. That is, most LMIC populations living in poverty do not develop mental illness. These findings called for further longitudinal research.
Another study done by Das et al. (2007) revisited the relationship using survey data from five LMIC: Bosnia and Herzegovina, Indonesia, Mexico, India and Tonga. Contrasting the findings of Patel & Kleinman et al. (2003), the study found that the relationship between consumption poverty and mental illness was poor while the strongest factors were widow-hood and poor physical health. It was hypothesised that the differences in the poverty-mental health relationship between developing and developed LMIC could be attributed to two causes. The first being the flexibility of work hours and attendance in LMIC in the informal sector (primary industries, self-employment), allowing individuals with mental illness opportunity to maintain employment. The second, larger village and family support systems lowering the risk of developing mental illness and insuring against poverty development.
Other additional findings of the report were that life changes – either positive or negative – had bigger, long-term impacts on mental health. Thus, Das et al. (2007) argued that public mental health interventions in LMIC should focus on individuals experiencing upheaval and adverse life changes.
However, a critique of Das et al. (2007) by Corrigall et al. (2008) expanded on certain limitations of the study. Firstly, it argued that the effect of downstream variables, such as age and poor health, is statistically larger than upstream variables, such as poverty. This is primarily because upstream variables exert their effect through downstream factors, resulting in poverty being less associated with mental illness. Secondly, the use of household expenditure (i.e. consumption poverty) as the measure of poverty could be misguided as the measure can be confounded with household debt. This itself has been found to be independently associated with poverty. Thirdly, their study contradicts the vast majority of community-based epidemiological studies that had been conducted in low, middle and high-income countries. Lastly, it was not clear whether a multivariate regression was performed.
In order to combat these issues, Lund et al. (2010) conducted a systematic review of the epidemiological literature in LMIC, using a variety of poverty measures. 79% of the 115 studies reviewed showed positive associations between different poverty measures and common mental disorders. However, there were differences in impact depending on the measure studied. Income, unemployment and consumption were less associated with CMD, whilst education, socio-economic status, food insecurity, housing, social class, financial stress were strongly and consistently associated. Lund et al. (2010) mentioned that such differences could account for the weak association between poverty and mental illness in LMIC as suggested by previous studies.
Lund et al. (2010) also noted that most of the 115 studies used in the reviews were cross-sectional. Thus, conclusions about the original cause in the interface between mental illness and poverty could not be drawn. It did, nevertheless, confirm that poverty and mental health most likely interact in a vicious cycle, as originally hypothesised. Individuals living in poverty are at risk of mental illness through high stressors, social exclusion, reduced social capital, malnutrition, increased risk for violence and trauma, and obstetrics risk. Concurrently, individuals with mental illness are inclined to be in poverty due to stigma surrounding mental illness, lost employment, school dropout and reduced social support.
In summary, the relationship between poverty and mental illness is complex and varied. Whilst a strong correlation between poverty and mental illness exists, there is also evidence to suggest the vice-versa – mental illness resulting in poverty. Hence, both social drift and social causation pathways are relevant in understanding poverty and mental health in LMIC.
Limitations and further areas of research
The limitations within the current body of literature indicates a wide scope for further research and improvement.
One of the most significant limitations of the literature thus far is accepting and validating definitions of poverty. The definition of ‘poverty’ has historically been controversial as it is imbued with socio-political ideological baggage. The lack of rigorous reporting of poverty indicators, and lack of consequent justification of the measures utilized based on current theoretical understanding in the field is concerning in this context. It impairs critical assessment and comparison across studies and consequently, future studies should focus on clearly defining variables with validated measures to be used.
In addition to more stringent quality of reporting, qualitative studies that reflect lived experiences would be a helpful contribution to this field as it may better capture the contextual differences across different developing countries as well as contribute to development of theoretical causality.
Given the complex interplay of factors that inform mental health outcomes in the context of multiple deprivation, further research is required to ascertain the strength of association amongst these factors. The ultimate goal is to identify those that may be protective in nature. Longitudinal epidemiological studies are required to establish direction of causality. Despite schizophrenia and bipolar disorders belonging to the top causes of disability in LIMC, there has been little effort to evaluate how these conditions uniquely interact with various determinants of poverty across an individual’s lifespan.[6, 18]
Further research is also required in evaluating the interventions targeting poverty and mental health in LMIC. Despite a clear positive trend between mental health interventions and improved economic outcomes in LMIC, the feasibility and efficacy in scaling up these interventions is unclear with macroeconomic costs involved in implementation and subsequent impact to be determined.
In reviewing the literature, it becomes clear that both the social drift and social causation theories are central to our understanding of the dynamic relationship between mental illness and poverty in LMIC. Of the measures examined, poverty, education, socio-economic status, food insecurity, housing, social class, financial stress were the most strongly associated with CMD, whilst income, employment and consumption did not having as significant an impact. Whilst correlations between poverty factors and mental illness have been established, causation has not. In this regard, longitudinal studies are important in establishing causality, with focus on the recognition of protective factors and time points for intervention in resource poor settings. As the degree of impact on mental illness is influenced by which poverty indicator is used, rigorous reporting of studies is critical to establish the framework which future studies will utilise to ultimately influence the development of effective policy.
Conflicts of interest
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