Effect of Early Health on Cognitive Ability

Carolina Milesi, University of Wisconsin at Madison

Research on social inequalities in health has consistently documented the inverse relationship between socioeconomic position and health (Marmot, Ryff, Bumpass, Shipley, and Marks 1997). Numerous studies have reported that higher levels of education, occupation, income, and wealth are associated with better health during adulthood. This social gradient in health has been observed for a wide range of outcomes, including physical and mental morbidity, psychological well-being, and mortality (Hertzman 1999). Only more recently however, health inequalities have been studied from a life course perspective, paying attention to the biological development and social pathways that lead to adult health (Wadsworth 1997). Within this approach, socioeconomic differentials in adult health are related to biological and social factors experienced across different life stages (Hertzman 1999). In Wadsworth’s words, “life history contributions to the study of inequalities in health show that health is a lifelong development for the individual.” (Wadsworth 1997: 867). In this context, the pathway between early childhood conditions and adult health is understood as one of the crucial processes through which socioeconomic inequalities in adult health are generated (Bosma, van de Mheen, and Mackenbach 1999; Hart, Hole, and Smith 2000; Smith, Hart, Blane, and Hole 1998; van de Mheen, Stronks, Looman, and Mackenbach 1998). The long-term impact of childhood on health and well-being operates both directly and indirectly through the cumulative effect of life events (Hertzman 1999). Recognition of the “long reach of childhood” (Wadsworth and Kuh 1997: 3) brings up the notion of health selection, according to which individuals’ health status affects their social position. Health selection is referred to by various terms in the literature, including reverse causation, health-related social mobility, occupational or social drift, social selection, and discrimination on the basis of health (Goldman 2001: 121). Goldman (2001) and Marmot et. al. (1997) distinguish between direct and indirect selection mechanisms. Direct selection occurs when health determines social position (Marmot et al. 1997: 907). This process is usually thought of as drift down the occupational class structure during adult life (West 1991). In the context of the long-term consequences of childhood however, this mechanism can be conceived as taking place when children with poor health (such as disabled children) are subject to downward mobility. Indirect selection on the other hand, arises when factors causally prior to adult health and social position – such as height, education, or parenting styles – determine both achieved social status and health condition in adulthood. This mechanism has been interpreted in terms of spuriousness, as if this explanation were asserting that there is no “real” causal connection between social circumstances in adult life and health status (Marmot et al. 1997). However, selection and causal mechanisms do not have be viewed as competing processes (Goldman 2001; Mulatu and Schooler 2002). As a social phenomenon in itself, health selection operates alongside a complex set of indirect causal pathways (Goldman 2001). Looking at this process over the length of the life course, West argues that the child-adult transition constitutes the stage at which health selection is more likely to occur (West 1991). West points out that in the debate on health inequalities, health selection appears as an “asocial” explanation in theoretical debt to social Darwinism (West 1991). In a debate characterized by the “either/or mentality” with respect to social and biological influences on health inequality, health selection is assumed to be a purely genetic process, therefore easily dismissed in favor of “social” causal explanations (West 1991: 379). West reformulates the health selection explanation as a form of discrimination, occurring via indirect mechanisms in the course of inter-generational mobility. He claims that “health selection – direct and indirect – does not occur in a social vacuum; it is the outcome of an interaction between more or less valued attributes of individuals and the opportunity structures and the institutions and social agencies which control access to and processes within them.” (West 1991: 380). According to West, the sorting and allocation of individuals with different health conditions is not a simple cause-effect process – with a fixed or inevitable outcome – but one shaped and mediated by a complex interconnected web of educational, training, and occupational processes, in which “health selectors themselves are a variable in the equation” (West 1991: 380). This paper builds upon this “social” formulation of the health selection argument. Cognitive ability is proposed as one of the mechanisms through which health selection takes place within and across generations. The substantial effect of cognitive ability on adult health (Deeg, Hofman, and van Zonneveld 1990; Korten et al. 1999; Smits, Deeg, Kriegsman, and Schmand 1999; Snowdon et al. 1996; Whalley et al. 2000; Whalley and Deary 2001), and on schooling, occupational attainment, and earnings (Cawley, Heckman, Lochner, and Vytlacil 2000; Sewell, Haller, and Portes 1969; Sewell and Hauser 1975) has been widely documented. Therefore, by analyzing the effect of early health on cognitive ability we are examining one of the roots of social and health inequalities in adult life. Three questions are posed: What is the effect of infant health on cognitive ability during childhood? To what extent is this effect mediated by “current” children’s and maternal