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Social Inequality in Physical and Mental Health Comorbidity Dynamics

From the Institute for Social and Economic Research (A.S.), University of Essex, Colchester, UK; Department of Epidemiology and Public Health (A.S., J.H., D.G., M.B.), University College London, London, UK; and the University of Texas School of Public Health (D.G.), San Antonio Regional Campus, San Antonio, Texas.

Address correspondence and reprint requests to Amanda Sacker, Institute for Social and Economic Research (ISER), University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK. E-mail: asacker{at}essex.ac.uk

Objective: To examine how socioeconomic position influences physical and mental health dynamics.

Methods: The Whitehall II study of civil servants collected questionnaires on six occasions from 1991/93 to 2006/07. Civil service grade measured socioeconomic position and Short Form 36 General Health Survey component scores rated physical and mental health. Bivariate growth curve models of physical and mental health over 15 years were estimated for high, medium, and low grades (n = 8309).

Results: At baseline, levels of physical and mental health were correlated for participants in low grades only. Among study participants in medium grades, mental health was maintained over time, even as physical health decreased. Restoring mental health after a negative response to poor physical health was more difficult for some in low grades. Recovery from downturns in physical health associated with poorer mental health also depended on better socioeconomic circumstances There was greater variability in baseline levels and rates of change in the mental and physical health of those in lower grades compared with higher grades.

Conclusions: Homeostatic mechanisms may vary by socioeconomic position. The greater variability of change in health function for those in lower grades implies considerable scope for improvement if sources of variation in health within disadvantaged groups that are amenable to intervention can be identified.

Key Words: aging • cohort studies • health functioning • longitudinal studies • socioeconomic factors

Abbreviations: SEP = socioeconomic position; GCM = growth curve model; SF-36 = Short Form 36 General Health Survey; PCS = physical health component score; MCS = mental health component score; BIC = Bayesian Information Criterion.