Copyright © 2004 by the Johns Hopkins Bloomberg School of Public Health
BOOK REVIEWS |
Health Inequalities: Lifecourse Approaches
Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
Edited by George Davey Smith
ISBN 1-86134-322-1, The Policy Press, Bristol, United Kingdom (Telephone: 44-(0)117-331-4054, Fax: 44-(0)117-331-4093, E-mail:tpp-info{at}bristol.ac.uk), 2003, 548 pp., $37.50 (paperback)
Increasing attention is being paid to the subject of health disparities across groups defined by socioeconomic position. As fresh observations of health disparities are added to the pile, two misleading arguments are often made: 1) that health disparities are new on the radar screen of epidemiology and public health and 2) that we do not know what mechanisms underlie these differences. Even the most casual review of the literature would quickly reveal that health disparities across socioeconomic strata have been studied at least as far back as the 1840s. The second argument (that we know little about what underlies these differences) is decidedly more difficult to support after reading the collected papers found in this volume.
This collection is an attempt to go beyond the further documentation of trends and patterns, to develop a theme, stimulated in part by Barker’s thesis of the fetal origins of adult disease (1). What is different and important about the papers collected here is the explicit attempt to explicate a lifecourse approach to the study of health inequalities. In his introduction, the editor illustrates the challenge by showing that simplified theories positing that only (very) early exposures are important or that only adult exposures are important have both been found wanting. What, then, do these papers tell us about the characteristics and potential advantages of a so-called lifecourse approach?
The papers collected here reflect epidemiologic puzzle solving done to a fine art. Across the span of these papers, the reader witnesses the evolution of "lifecourse epidemiology." A nice example is the use of deduction and data to isolate the influence of early childhood socioeconomic status from adulthood exposures in chapter 17. They find evidence that childhood socioeconomic status contributes significantly to the risks of both stroke and stomach cancer, independent of adult socioeconomic status. At times, the limitations of the data and the grand spaces between speculations caused this reader to stumble and say "hmmmm." Stomach cancer has seen the most dramatic declines in mortality (among cancers) over the last several decades, with stroke having less impressive but significant declines. This raises the possibility that birth cohort effects masquerade as early exposure, less net adult exposure effects. Too little is made also of the lack of association between cardiovascular mortality (the sacred cow of the early exposure school) and parental social class once the influences of adult class and risk factors have been removed. In several of the papers, the failure of various data sets to support the Barker hypothesis with regard to heart disease deserved more self-critical discussion.
What can we conclude from this anthology is the essence of a lifecourse approach? Two general themes are reflected here: 1) that early life exposure leaves a legacy of risk that is a powerful component of explaining socioeconomic gradients of adult disease and mortality, and 2) that risk factors accumulate and interact synergistically over the lifecourse in ways that are decidedly complex. However, as work in sociology and human development has shown, the lifecourse approach has other features not yet fully developed or even visible in lifecourse epidemiology. An important example is Featherman and Lerner’s concept of duration dependence (2), which supposes that developmental explanations must take explicit account of the timing and duration of exposures across the life span. A related concept is the idea of specific windows of high vulnerability to risk exposure across the life course. Yes, exposure to noxious material conditions in childhood is important, but for different outcomes, some periods of exposure are likely to be of greater etiologic significance than others. Developmental psychologists are considerably ahead of epidemiologists in this regard; see, for example, the publications by Baltes et al. (3) and Garbarino (4). This volume shows that lifecourse approaches have much to offer; however, a more mature lifecourse approach is somewhere in the future.
An ongoing debate between the editor and proponents of a "psychosocial" approach to explaining socioeconomic status disparities in adult health can be clearly discerned throughout much of this volume (see, especially, chapter 34). This reviewer has always found this feud to be unfortunate and tedious. The editor (and author of most of the papers) interprets the body of collected evidence as demonstrating that a lifecourse approach favors a materialist explanation of health disparities. At several points, they show that the effect of psychosocial variables (such as social capital or income inequality) dissipates when appropriate controls for early life exposure to deprived material conditions are applied. If there is one important lesson to be learned from lifecourse approaches in the social sciences, it is that we require explicit theories to determine which variables are confounders and which are mediators. Statistically controlling on hypothesized mediators is bad science. Lifecourse analysts in the social sciences invented and propagated innovative modeling approaches (such as path analysis and structural equations models) for dealing with explicit hypotheses about duration dependence, time lags, and effect mediation 30 years ago. Social epidemiologists interested in psychosocial processes (relative deprivation, for example) have argued that material conditions act through (not against) and are mediated by these processes. As Macintyre et al. (5) and others have noted, it is time that we bury this well-beaten horse and get beyond black-and-white, either/or debates about material versus psychosocial explanations. A more mature lifecourse epidemiology will require that we adopt modeling approaches that can support and test developmental theories. This will require us to question the philosophy of independent causal effects so sacred in epidemiology.
In summary, the reader will find an engaging and important body of work collected in these pages. This work illustrates the power of lifecourse epidemiology to make real headway in explaining the mechanisms that lead to health disparities later in life. These chapters also reflect the mischievousness and wide-ranging interests of the editor (see the chapters on mortality patterns in pets (chapter 27) and on the health effects of sexual intercourse (chapter 29)). One can quibble about whether there is much new in this collection of previously published papers. My conclusion is that the sum is worth more than the parts.
REFERENCES
REFERENCES
- Barker DJ. The foetal and infant origins of inequalities in health in Britain. J Public Health Med 1991;13:64–8.
[Free Full Text] - Featherman DL, Lerner RM. Ontogenesis and sociogenesis: problematics for theory and research about development and socialization across the lifespan. Am Sociol Rev 1985;50:659–76.[CrossRef]
- Baltes PB, Featherman DL, Lerner RM, eds. Life-span development and behavior. Mahwah, NJ: Lawrence Erlbaum Associates, Inc, 1990.
- Garbarino J. Adolescent development: an ecological perspective. Columbus, OH: Charles E. Merrill Publishing Company, 1985.
- Macintyre S, Ellaway A, Cummins S. Place effects on health: how can we conceptualise, operationalise and measure them? Soc Sci Med 2002;55:125–39.[CrossRef][Web of Science][Medline]
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