Severe mental illness has been associated with an increased risk of mortality. Findings from a recent study conducted in the UK and published in the Lancet Psychiatry suggest that severe mental illness and excess mortality in ethnic minorities may be of particular concern, as minority groups experience higher rates of mortality relative to the general population.
Severe mental illness includes disorders like schizophrenia, schizoaffective disorders, and bipolar affective disorders. Studies have shown that people with severe mental illness have higher rates of mortality compared to the general population. Excess mortality in this population has been linked to natural and unnatural causes, although it is unclear whether mortality rates vary by ethnicity. As ethnic minorities already experience excess mortality from natural causes like diabetes and cardiovascular disease, those with severe mental illness may be particularly disadvantaged. Contrary to this expectation, a study conducted in the US in 2015 showed that ethnic minorities with schizophrenia had lower rates of excess mortality from natural and unnatural causes, compared to non-Hispanic whites with the disease.
Given the puzzling nature of these findings, and because few studies of this nature have been conducted outside of the US, researchers in the UK designed a study to investigate the risk of mortality among black Caribbean, black African, south Asian, Irish, and white British individuals with severe mental illness, compared to the risk of mortality among the general population of England and Wales. The longitudinal cohort study, published in the Lancet Psychiatry, was conducted from 2007 to 2014. It was based on secondary data collected from medical records. A sample of 18,201 people diagnosed with schizophrenia spectrum or bipolar disorders were included in the study.
Participants were identified anonymously through a search of electronic medical records in a case registry of the South London Maudsley Trust (SLaM), an ethnically diverse area in London, UK. Participants had previous contact with SLaM psychiatry services, and they were older than 15 at the time of diagnosis. Researchers also included mortality data from the general population in England and Wales. These data were collected from records maintained by the UK National Office of Statistics; they allowed researchers to calculate standardized mortality ratios based on age and sex of the general population to compare the mortality risk of people in the study sample to mortality risk in the general population.
Participants were followed across time until they died, emigrated, or until the study period ended. For those who died over the course of the study, mortality was classified based on death certificates as all-cause, natural-cause, or unnatural-cause mortality. Natural-cause mortality included deaths from cancer and respiratory and circulatory diseases, while unnatural-cause mortality involved suicide, self-harm, or death from events of undetermined intent. Researchers also collected sociodemographic data including date of birth, sex, diagnosis (i.e., affective or non-affective), marital status, comorbid alcohol and substance use/misuse diagnoses, and self-ascribed ethnicity. For the purposes of the present study, schizophrenia spectrum disorders were classified as non-affective disorders, and bipolar disorders as affective disorders.
By the end of the study period, 1,767 participants had died. Regardless of their ethnicity, findings indicated that individuals with severe mental illness have an increased risk of mortality from suicides, non-suicide unnatural causes, respiratory and cardiovascular disease, and cancers. When compared to the general population, they were 5-10 times more likely to die from suicide and about 4 times more likely to die from respiratory or cardiovascular disease. These risks were similar across all five ethnic groups, although south Asians had a slightly reduced risk of cancer mortality. When individuals with severe mental illness in the other ethnic groups were compared to white British individuals with severe mental illness, black Africans and black Caribbeans had reduced mortality for all causes, natural causes, and unnatural causes, and south Asians showed a similar pattern of results for natural-cause mortality.
The researchers also assessed associations between diagnosis, sex, marital status, alcohol and substance misuse, and mortality risk. Comorbid alcohol and substance misuse diagnoses were associated with an increased risk of all-cause mortality and they doubled the risk of unnatural-cause mortality. Being single, separated, divorced, or widowed also increased risk for all-cause mortality. Compared to males, females had a lower risk of all-cause and natural-cause mortality. Similarly, affective diagnoses (i.e., bipolar disorders) were associated with a lower risk of all-cause and natural-cause mortality relative to non-affective disorders.
The large, ethnically diverse cohort and the 8-year observation period used in this study allowed researchers to assess differences in mortality based on self-ascribed ethnic status across five ethnic groups. The researchers also accounted for emigration out of the cohort, which could result in an underestimation of mortality risk as migrants who return home when they fall ill are not included in research. Despite these strengths, the researchers were unable to assess differences in ethnicity within the south Asian group, which included Indian, Pakistani, and Bangladeshi individuals. Further, diagnosis of mental illness was not based on research criteria, and may have been racially biased if clinicians are more likely to assign a diagnosis of severe mental illness to people of particular ethnic origin.
Further research is needed to explore the association between severe mental illness and excess mortality in ethnic minorities relative to the general population. In particular, the mechanisms underlying mortality risk deserve further attention. Additionally, findings that suggest reduced mortality in ethnic minority individuals relative to their white British counterparts would benefit from further study. Social factors like social support and cultural practices may serve as protective factors for ethnic minorities, especially those who live among family and friends who have immigrated.
Written By: Suzanne M. Robertson, Ph.D