Impact of socioeconomic deprivation on rate and cause of death in severe mental illness

It is recognised that socioeconomic status has a significant impact on health and wellbeing and, with only a few exceptions, health outcomes are generally worse in deprived communities [1]. In Western societies, although there is evidence of equity in access to primary care services across different socioeconomic profiles, there is also evidence of inequalities in access to more specialist services [2],[3]. In Scotland, which has had the highest mortality in Western Europe among working age (15-74 years) men and women since the late 1970s [4], premature mortality and inequalities in healthcare remain important [5],[6]. In 2010 it was estimated that Scottish male mortality rates were around 20% higher and female working age mortality 30% higher than the Western European mean. Although Scotland has been dubbed the “Sick Man of Europe”, its biggest city Glasgow has even higher mortality rates, along with higher rates of deaths from suicide, drugs and alcohol and lower life expectancy than the rest of Scotland [7]. While it is known that the impact of deprivation on health and mortality is large, the differences in life expectancy in Scotland compared to the rest of Europe (and in Glasgow compared to the rest of Scotland) cannot be fully explained by differences in its deprivation profile alone. These differences which are unexplained by deprivation have been termed the “Scottish” and “Glasgow” Effects.

For individuals with SMI, the increase in standardised mortality rates (SMRs) compared to the general population is substantial [8]-[11]. On average, men with schizophrenia die 20 years earlier and women die 15 years earlier than the general population [12],[13]. For bipolar disorder, life expectancy is estimated to be reduced by approximately 10 years in men and 11 years in women [11]. Furthermore, there is recent evidence from the UK [12], US [13] and Western Australia [14] to suggest that this mortality gap may be getting worse. Although it is recognised that individuals with SMI have more physical health problems than the general population [15],[16], there is also evidence of inequalities for both access to and the quality of a range of physical healthcare services [17]-[21]. In combination with the inequality in access to treatment, it is recognised that SMI individuals tend to experience a greater downward trend in socioeconomic status over time compared to the general population [22]. Despite the important and complex interaction between socioeconomic status and mortality, little work has specifically focused on this relationship for individuals with SMI. Here we describe and compare rates and causes of death for individuals with schizophrenia and bipolar disorder who were registered on the Glasgow Psychosis Clinical Information System (PsyCIS) according to socioeconomic quintile, relative to the local Glasgow population and the wider Scottish population. We seek to determine if as is seen in the general population, increasing deprivation is associated with increased mortality rates and we also examined whether or not the “Glasgow” Effect was present in our cohort of individuals with SMI.

We used the Scottish Index of Multiple Deprivation (SIMD) score as a measure of social deprivation. The SIMD identifies small areas of multiple deprivation (datazones) across Scotland by combining 38 indicators across 7 domains which are weighted. The domains include: current income, employment, health, education, geographic access to services, crime, and housing and are weighted based on evidence from Oxford University’s Social Disadvantage Research Centre [27]. Each domain contains information gathered from multiple sources, for example the health domain contains information regarding: hospital episodes related to alcohol use, hospital episodes related to drug use, a measure of mortality (the comparative mortality factor (CMF)), a measure of morbidity (comparative illness factor), emergency admission to hospital, population proportion prescribed drugs for anxiety, depression or psychosis and proportion of singleton births of low birth weight (<2,500 g). Each individual was allocated to a datazone and subsequent SIMD category based on their postcode (1 = most affluent and 5 = most deprived). There are 6,505 datazones covering Scotland and the SIMD score provides a relative measure of deprivation.

Our cohort of individuals with SMI had higher mortality rates compared to both the local Glasgow and wider Scottish populations, consistent with several other studies which have used similar secondary care mental health registers [28]-[30]. The proportion of deaths by age group was similar to that seen in the local Glasgow population, but differed from that of the wider Scottish population, with a larger proportion of deaths occurring in those aged 25-44 years with SMI. As occurs in the general population, increasing socioeconomic deprivation appeared to be associated with an increased overall rate of death in those with SMI.

In our cohort of patients with SMI the rate and cause of death differed from that of the local Glasgow and wider Scottish populations. There appeared to be a graded effect of deprivation on mortality, which was largest in impact for those with SMI when suicide was excluded as a cause of death. This pattern of rising mortality across deprivation categories may represent evidence of inequalities in health outcomes for the most deprived individuals with SMI. More work is required to investigate this relationship further, in order to inform new approaches to health care organisation, health promotion and screening in those with SMI living in the most deprived communities.