Mental health disorders should be a first order concern for development practitioners, particularly as they disproportionately affect the most vulnerable segments of society. As this column outlines, an emerging body of research evidence shows how mental health is affected by climate change and by early life conditions as far back as fetal origins. It is essential to develop a better understanding of the mechanisms by which climatic shocks, and more broadly, early life shocks, affect adult mental health—and how policy can respond to those challenges.
Despite the substantial interest of development practitioners in health and disease, relatively little attention is given to mental health. This is surprising since mental health is extremely costly. Not only is it the leading global cause of people living with a disability worldwide, but it is also the leading source of disease burden for women.
Beyond the significant direct costs of mental health for general health, it is likely that it also affects decision-making, inhibiting productivity and leading to adverse life outcomes. While rarely studied, the evidence finds important impacts on both labor market participation and earnings across a range of disorders. Taken together, mental health disorders are a first order development concern.
Although developing countries are believed to be particularly affected, the actual prevalence of mental health disorders is largely unknown. Beyond the associated stigma, mental illnesses are rarely diagnosed or treated. In less developed countries, roughly 80% of serious cases of mental disorders do not receive treatment in the preceding year. Less serious cases, which are more numerous, are even less likely to be treated.
The available data suggest that roughly 20–30% of the population in developing countries may have mental disorders. Indeed, in our own work on a representative sample of the Indonesian population, we find that almost a quarter of people are symptomatic of depression (based on the Center for Epidemiological Studies Depression, CESD-10, module, a widely used measure). Within developing countries, mental illnesses particularly affect the less educated, the poor and women—all groups of particular concern to policy-makers.
Although adult mental health is strongly influenced by current circumstances, a multidisciplinary body of research evidence is highlighting the additional importance of early life conditions, beginning in pregnancy. These include experiences that are specific to individuals (such as family ruptures and early life stress, including many types of abuse) as well as large shocks that affect wide swathes of the population.
While early life exposure to substantial shocks, such as famines and natural disasters, shapes subsequent adult mental health, recent research finds important effects from exposure to relatively banal events.
Due to the importance of agriculture and the prevalence of informal sector jobs, large segments of the population in developing countries are exposed to income variation. The limited availability and efficiency of strategies for coping with risk means that this variation frequently translates into similar variation in consumption.
Exposure to early variation in income has been widely linked to anthropometric and cognitive outcomes and, in recent work, it is linked to adult mental distress. In particular, that study examines whether changes in income from exogenous changes in cocoa prices affect the mental distress outcomes of children by comparing those from cocoa and non-cocoa producing regions in Ghana.
The authors find that a one standard deviation decrease in the log of prices increases the prevalence of severe mental distress by 3%, or roughly 50% of the mean. In the context of the study, this means that individuals exposed to a roughly 12% decrease in cocoa prices (relative to the mean) in early life are 50% more likely to report severe distress.
These results—and those of related studies—demonstrate the link between early life conditions and adult mental health. But due to the strong relationship between early life shocks and a variety of other adverse outcomes, it is not possible to isolate the exact role of mental health.
For example, lower mental health may be an outcome of the lower adult, educational, and health outcomes for children exposed to early life shocks. Alternatively (or concurrently), lower mental health from the shocks could lead to lower adult educational and health outcomes.
Irrespective, early life interventions may have important consequences. For example, the study on income changes and adult mental health implies that income/consumption stabilization programs can play an important role in reducing the prevalence of adult mental health disorders.
These programs will vary based on the settings. In agricultural settings, they could relate to stabilizing output prices, providing safety nets or work programs (such as India’s NREGA, the Mahatma Gandhi National Rural Employment Guarantee Act), providing price/weather insurance, or helping households to become more resilient to such shocks—for example, by introducing more resilient crops.
Beyond income shocks, it is likely that climatic variation also plays an important role, with recent studies pointing to variation in heat and rainfall levels. The first of these two studies uses data on more than 60,000 adults in 19 African countries to examine the effect of exposure to early life temperature variation. The researchers find that pre-natal exposure to a year that is one degree warmer than the local historical average raises the probability of at least moderate depression by 1.3 percentage points.
Our own study looks at the effect of early life exposure to above average (but still common) levels of rainfall in Indonesia on CESD-10 scores. Early life post-natal exposure increases the likelihood of being symptomatic of depression by 5%, a more than 20% increase relative to the mean. As in another recent study, these effects are limited to women.
It is notable that income does not seem to be the pathway from rainfall shocks to lower adult mental health. First, rainfall shocks are typically viewed as income shocks and, in conjunction, with the earlier study on early life income, one would expect this to reflect an income shock.
Second, we find evidence pointing towards the disease environment. Not only does this potentially explain earlier studies linking early exposure to malaria with lower adult outcomes, but it also suggests more complicated mechanisms linking early shocks to adult mental health. Importantly, if mental health disorders are not caused by income fluctuations, they may not necessarily respond to income transfers or stabilization programs. But our results are also consistent with other explanations, such as the duration of breastfeeding.
With projected increases in climate variability, this body of evidence suggests that mental health may deteriorate, especially since the relationship between climate and health does not appear to change. For example, the study of early life exposure to temperature variation finds a consistent effect across time: improvements in access to health, income and other measures do not change this relationship.
Unfortunately, despite the apparent importance of weather, there is very limited research on how to address this challenge. While increasing the diagnoses and treatment of mental health is important, more pro-active measures should play an important role.
Far more attention and research are needed to develop a better understanding of the mechanisms by which climatic shocks and, more broadly, early life shocks, affect adult mental health.