This life-course study, spanning the period from birth to age 26 years, shows that low childhood socioeconomic circumstances have long-lasting negative influences on adult health, irrespective of what health cache one begins life with, or where one ends up in the socioeconomic hierarchy as an adult. Specifically, the findings document that the social gradient in health—which has been amply documented among middle-aged and older adults—actually emerges in childhood. Whereas clinical and research interest in the social gradient has been generated mostly by studies of adults, the findings from this study suggest that the social gradient must be scrutinised in paediatric and adolescent populations as well. Further, whereas most studies of the social gradient have narrowed their attention to specific diseases, such as cardiovascular diseases, we document that the social gradient is far more ubiquitous and troubling. Low social class adversely affects many areas of people’s health, including their physical, dental and mental health.
These findings do not mean that adult social class is inconsequential for health. Four findings underscore the contribution of contemporaneous adult socioeconomic status. First, both low-childhood and low-adult status were related to poor cardiorespiratory fitness and poor dental health (table), suggesting that exposure to adverse environments in childhood and in adulthood contribute additively to some adult health risks.3,13,17
Second, upward mobility from childhood to adulthood was associated with lower waist:hip ratio (). Third, downward mobility from childhood to adulthood was associated with poorer fitness and poorer dental health (). Finally, depression and tobacco dependence were more strongly linked to adult socioeconomic status than to childhood socioeconomic status (table), suggesting that proximal experiences in adulthood better account for the association between low socioeconomic status and these mental health disorders.24
Several limitations are apparent. First, our measure of childhood socioeconomic origins was limited to parental occupational status and did not incorporate all potential indicators of social inequality.25
However, in so far as childhood social origins were measured contemporaneously, directly, and across the entire childhood period, this method represents improvement on previous attempts to identify childhood socioeconomic status via adult recall or through proxy measurements. Second, adult socioeconomic status at age 26 years might not reflect final socioeconomic destination, and adult achievements later in life might increasingly undo earlier childhood influences. However, most of the Dunedin Study members have completed their formal education, and rates of adult return to education in New Zealand are low. Because educational attainment is an excellent predictor of socioeconomic status at midlife (age 50 years),15
we repeated all analyses substituting a measure of the study members’ educational achievement for the measure of adult occupational status, categorised as no or little school qualification (School Certificate [roughly equivalent to the British General Certificate in Secondary Education] or less; n=304, 31%); 6th Form Certificate (equivalent to British A-levels or a US high school degree; n=461, 47%); and bachelors degree or higher (n=215, 22%). We obtained the same pattern of results, suggesting that the influence of childhood socioeconomic status is unlikely to vanish. Finally, the findings from this contemporary New Zealand cohort (born 1972–73) require replication in other parts of the world. Previous studies examined links between childhood socioeconomic status and adult mortality and morbidity in older cohorts (born 1906–58),6,13,17,26
but our study suggests that these links continue to hold today. Moreover, childhood socioeconomic status has pervasive effects on adult health despite the fact that members of this contemporary cohort grew up with access to universal subsidised health care.
The present study provides a strong test of the effect of childhood socioeconomic experiences on adult health, while ruling out potential alternative explanations. Research now needs to identify the key mechanisms that bring about this longitudinal association. Although lack of resources and structural impediments (eg, lack of community facilities for physical activities) might play a part, the breadth of adult-health variables affected (ranging across physical health, dental health, and substance abuse) suggests several other candidate mechanisms.26
First, class-biased health-care delivery during children’s formative years might create long-lasting health inequalities. Second, social-class related differences in health-promoting parenting practices might contribute to early-emerging and long-lasting health differences among children.27
Finally, social-class related stressors in childhood might alter biological systems and exert long-lasting influences on adult health.28
Developmental studies, in particular, should focus on health-related parenting practices and on the nature of stressors experienced by children in different social strata to provide insight into the origins of the enduring association between childhood socioeconomic status and adult health.29
If risk for later morbidity is influenced by early life circumstances, efforts to reduce health inequalities must begin as early as practicable to ensure the greatest impact on burden of disease.30