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Description
Background: Research has shown that income is a fundamental determinant in population health; however, little research has examined the relationship between income and health in a birth-cohort dimension. Objectives: Based on the fundamental cause theory and life-course theory, we examined income gradients in obesity among whites and blacks across cohorts (chapter 1) and assessed the effects of economic conditions in early life and income inequalities in early life on the risk of all-cause and cause-specific mortality (chapter 2 and 3). Methods: In chapter 1, we fitted a series of logistic hierarchical Age-Period- Cohort models using the National Health and Nutrition Examination Survey (1971- 2012). Predicted probabilities of obesity by poverty income ratio were estimated based on the models and graphed for 5-year cohort groups from 1901-1990. We also stratified this relationship for four gender and race/ethnicity subgroups. For chapter 2 and 3, we employed parametric frailty survival models using linked General Social Survey and National Death Index data (1979-2008). Gender-stratified analyses were conducted on the all-cause and disease-specific mortality. To better understand the underlying mechanisms, we further examined interactions between the macro-level income status in early life and parental education on adult mortality. Results: Analyses in the chapter 1 revealed that the weaker income gradients in obesity were found in post-world war generations, mid-1920s, mid-1940s, and 1950s cohorts (absolute index: 0.03-0.08; relative index: 1.14-1.35), than the other cohorts. Moreover, cohort-based income gradients in obesity vary markedly by gender and race/ethnicity. In the second study, we found that exposure to recession in the first year of life was associated with an increase all-cause mortality only among women (hazard ratio=1.54, 95% CI 1.03-2.31) and mortality from cancers (hazard ratio=2.24, 95% CI 1.18-4.28). In the third study, we found that a higher level of income inequalities in early life was associated with increased risk of all-cause mortality among males (hazard ratio=1.038-1.041, 95% CI 1.001-1.070) and mortality from various diseases. Paternal education moderates these relationships for the second and third study. Conclusion: Cohort-specific strategies based on life-course approach are needed to improve population health status and tackle socioeconomic disparities in health.
