The study
Socioeconomic status is a powerful predictor of ill health. It is already known that having two or more diseases and developing multimorbidity is more common among the poor. Prof Mika Kivimäki et al investigated the temporal sequence in relation to poor socio-economic status and the emergence of a large group of mental disorders by combining data from two large Finnish cohort studies. The combined sample had 109246 participants. The relationship pattern was then checked with a third cohort ( the famous Whitehall 2 UK cohort). Residential area deprivation ( an aggregate measure of low education, unemployment rate, and proportion of people living in small rented housing), educational attainment, and employment grade ( in Whitehall study) were the indicators of socioeconomic position. All relationships between socioeconomic status and disorders were adjusted for lifestyle factors ( smoking, risky alcohol use, physical inactivity, and obesity). National electronic records provided hospital treatment and mortality data for all subjects.
Results
low socioeconomic status was strongly associated with one-third of the 56 diseases studied, independent of lifestyle factors. This included 16 strongly interconnected ( directly or indirectly ) conditions (hazard ratio >5 for each disease to be followed by another disease). A cascade can be seen clearly. This started with psychiatric disorders, substance abuse, and self-harm and was followed later by diseases of the pancreas, liver, kidney, vascular and respiratory system, lung cancer, and dementia. The analysis also shows the bidirectional nature of the relationship between mental and physical disorders.
Limitations
The study covers conditions that resulted in hospital treatment only. It is very likely that a larger proportion of the socio-economically disadvantaged population would be still having mental and physical morbidities ( but not requiring hospital treatment ) and these could also follow the same association and cascade pattern ie poor mental health could be a starting point that leads to poor physical health. Adjusting for confounding factors ( lifestyle factors) is conservatory (mostly self-reported parameters only), but still meaningful. The study does not cover children or very old people.
Strengths
This study has been able to look at a wider range of disorders than previous works. It has a very large longitudinal sample size with minimal sample attrition after baseline.
Conclusions
Low socioeconomic status is a risk factor for a spectrum of interconnected diseases and health conditions. The morbidity trajectory is very illuminating of the larger and varied physical health risk of being poor.
This important work highlights the importance of mental health and behavioral problems as the starting points for many physical disorders among the socio-economically disadvantaged.
Unfortunately, our current global initiatives and goals do not include socioeconomic disadvantage as a modifiable risk factor. Care for mental disorders and poor mental health should become a priority if we are to promote the better physical health of the population, especially among the disadvantaged classes.
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