ArticlesOrigins of health inequalities in a national population sample
Introduction
Inequalities in health are believed to result from differences in exposure to an accumulation of health-damaging or health-promoting physical and social environments among different groups.1 Although exposure to adverse factors occurs at different stages in life and accumulates over time, current evidence on disease risk and social position is predominantly either cross-sectional or from studies with limited information on early life. One especially informative example is the Whiteheall II study,2 which showed systematic variation by employment grade in several potential biological, behavioural, and psychosocial risk factors, with adverse factors clustering in the lower grades. A 1997 study3 of Finnish men also showed that adult-disease risks vary systematically, but in this case with indicators of social position in childhood.
What has not been established is the extent to which risks accumulate differentially by social position at each stage in life over a substantial period of the lifespan. Few studies have the necessary longitudinal data that include a record of early-life factors. There is evidence, however, that several early-life factors should be considered in relation to adult disease, even though the processes linking early and late life remain contentious.4, 5 For example, growth in utero and during infancy may affect the risk of chronic adult diseases, such as cardiovascular disease, obstructive lung disease, and diabetes.6, 7 Height is associated with mortality, particularly for respiratory and cardiovascular disease,8, 9 which suggests that childhood socioeconomic circumstances might have long-lasting effects on mortality. When investigators examined childhood socioeconomic status more directly, with information on the father's occupation or economic status, they found associations with adult mortality—in some instances reflecting the link between childhood socioeconomic status and later education or adult position.10, 11, 12 An accumulation of both childhood and adulthood factors was related to adult respiratory morbidity, including, as risk factors, childhood respiratory illness, low socioeconomic status, atmospheric pollution, and smoking.13 Other studies have shown associations between parental divorce and psychological health and longevity in adulthood.14, 15 This finding is believed to reflect other factors, such as parental conflict, rather than parental loss. Given that many childhood adversities may operate partly through intermediate factors, such as educational achievement,5 both early and intermediate influences on health inequalities must be explored.
Using early-life risk factors for adult disease identified from previous reports, we examined the extent to which social trends in these factors vary systematically throughout early life (from birth to young adulthood). We used longitudinal data from the 1958 birth cohort in England, Scotland, and Wales, from the original birth survey through to age 33 years. Our study thus provides data on differential accumulation of risk in the same individuals followed up over three decades.
Section snippets
Study sample
The 1958 birth cohort includes all children born in England, Wales, and Scotland during March 3–9, 1958. The study originated in the Perinatal Mortality Study, which recorded information on 17 414 (98%) births. Follow-up surveys were undertaken when the participants were aged 7, 11, 16, 23, and 33 years, with 11 407 participants interviewed in the latest survey.16 Those remaining in the study are generally representative of the original sample.16, 17 Information at ages 23 and 33 was obtained
Morbidity in early adulthood and social-class origins
Table 1 shows health status at age 33 according to class at birth. A social gradient was evident for several health measures, with increasing prevalence from classes I and II to classes IV and V. The trends were especially strong for men and women with poor-rated health, respiratory symptoms, and psychological distress, and for women with menstrual problems. Weaker trends were evident for long-standing illness, back pain, and migraine among women but not among men. Few health indicators showed
Discussion
In a cohort of people who have been followed up for 33 years since birth, strong associations have emerged between social class at birth and accumulation of risk factors for adult health. These multiple health risks are not predetermined, but are greatly influenced by social origins. By age 33, health gradients are already well established. In this study, health gradients cannot be attributed to selective social mobility because social class was based on the father's occupation in 1958 and was
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