Department of Maternal and Child Health, Harvard School of Public Health, and the Centers for Behavioral and Preventive Medicine, Brown Medical School and The Miriam Hospital.
Stephen E Gilman, Department of Maternal and Child Health, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA. E-mail: sgilman{at}hsph.harvard.edu
The paper by Harper et al.1 in this issue of the International Journal of Epidemiology provides new evidence that childhood socioeconomic conditions matter for adult mental health. Their study joins many others in showing thatat the very beginning of lifesocioeconomic stratification sets the stage for the exposure to risks that eventually lead to diseases of diverse aetiologies.2,3
Harper et al. studied 2585 Finnish men, and found that those of lower childhood socioeconomic status (SES), indexed by parental occupation and education, had significantly higher mean values on scales of cynical hostility, hopelessness, and depressive symptoms. On the basis of multiple regression models estimated separately for both childhood SES indicators, parental occupation and education had comparable effects on the psychosocial outcomes. These effects were slightly attenuated when both childhood SES indicators were modelled simultaneously, and were further attenuated after the subject's own SES was controlled for; however, childhood SES remained significantly related to cynical hostility and hopelessness, although not depressive symptoms. It is possible that the lower reliability of the depression index in this sample and the assessment of depression on a current rather than lifetime basis contributed to the weak association between childhood SES and adult depressive symptoms.
While these analyses can be criticized for the use of retrospective reports of childhood SES, adults do seem to be able to accurately recall their parents' SES at the time of their childhood.4 Whether or not high levels of hostility, hopelessness, and depressive symptoms influence the reporting of childhood SES is less clear. In light of evidence that current mood impacts certain aspects of memory,5,6 this issue remains a concern.
Interpretation of the results of this study depends on our ability to gauge the location and magnitude of the differences in hostility, hopelessness, and depressive symptoms that were observed between men of lower versus higher childhood SES. By location, I refer to the question of whether SES differences in the psychosocial outcomes lie entirely within the normal range of functioning or whether they shift individuals into the severe range of a normal distribution. Regarding magnitude, I refer to the issue of whether the effects are meaningful, that is, are of clinical significance'. To address both of these questions, additional information is needed, such as the correlation of the psychosocial outcomes with psychiatric diagnoses, and the level of functional impairment associated with high scores for hostility, hopelessness, and depressive symptoms. Yet, as Harper et al. maintain, even small effects that exist at any single point in time may accumulate over the life course and lead to significant impairment. However, SES indicators obtained at multiple life stages are needed to directly test accumulation hypotheses (for example, see Holland et al.).7
The study by Harper et al. brings to the fore two important challenges for researchers conducting epidemiological investigations within a life course framework.
Challenge 1: The Use of Socioeconomic Status in Life Course Epidemiology
Epidemiological investigations into socioeconomic gradients in disease are often criticized as Black Box' epidemiology because explanations for such gradients are seldom elucidated.8 In addition, the tendency to use measures of socioeconomic conditions interchangeably makes it difficult to generate hypotheses regarding the specific domains of SES that are relevant for any particular outcome. This lack of clarity is especially problematic for studies investigating the effects of SES across the life course. The reason for this is that we tend to regard the most common indicators of SESi.e. education, occupation, and incomeas attributes of individuals rather than of contexts. This is an incorrect assumption in life course' studies, wherein parents' SES is used to represent their children's socioeconomic context. And despite considerable shared variation between indicators of parental SES, they may not be entirely redundant, with the variance specific to each measure of parental SES reflecting distinct aspects of the childhood environment that impact long-term health.
It is notable that Harper et al. considered two aspects of children's socioeconomic context, parental education and occupation, and hypothesized that each represents a different component of the childhood environment, i.e. children's intellectual and material resources respectively. As parental education and occupation were found to have independent effects on adult cynical hostility and hopelessness, it is possible to conclude that both of these domains are important for adult well-being. It is important to distinguish between the two hypotheses presented here. The first, or measurement' hypothesis, is that parental education and occupation reflect different aspects of the childhood environment. The second, or causal' hypothesis, is that both of the domains measured by parental education and occupation influence adult well-being. Further research is needed to explicitly test both of these hypotheses.
Challenge 2: Identifying Common Pathways
To a large extent, the focus of life course epidemiology has been the correlation of childhood factors with single adult health conditions, leading investigators to call for future studies of the pathways between childhood risks and specific adult disorders. Harper et al. have gone beyond this by analysing multiple, albeit related, dimensions of adult psychosocial health. Their finding that childhood conditions predict multiple aspects of adult functioning may lead one to hypothesize that common pathways exist linking early life SES to adult health. The identification of common pathways has substantial public health relevance for the translation of life course epidemiology into practice; this is because interventions that target common pathways have the potential to reduce morbidity related to multiple conditions.
Perhaps the most frequently hypothesized pathwayor mediating variablebetween childhood SES and adult health is adult SES. Adult SES is considered a pathway because it is heavily influenced by childhood SES (for example, see Power and Matthews regarding this issue in the 1958 British Birth Cohort9) and is itself predictive of subsequent health outcomes, including the ones studied by Harper et al.10 While Harper et al. found that childhood SES remained significantly associated with measures of adult psychosocial functioning after adult SES was controlled for, Lynch et al. previously reported thatin the same samplechildhood SES did not predict adult mortality independent of adult SES.11 Taken together, these findings indicate that adult SES is one, but not the only, pathway linking childhood SES to adult health. For those life course associations that are mediated by adult SES, programmes aimed at reducing adult SES gradients in health are needed.12,13 Even without a complete understanding of the pathways involved, though, research on the life course effects of childhood SES supports the assertion that improving the socioeconomic conditions of children14,15 would have a long-term benefit for adult health and may be an especially powerful avenue towards the reduction of health inequalities.
Acknowledgments
Support received from the National Institute of Mental Health, grant MH 61953.
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