Parental income gradients in adult health: a national cohort study

Individuals with low income tend to have worse health than those with higher incomes, and trends over the last decades reveal increasing health inequalities in many countries [1‐6]. Strong socioeconomic gradients in health are also found in Scandinavia [7‐9] despite universal access to publicly financed health services, free education, and strong welfare-state institutions [10]. Moreover, economic inequalities are also on the rise in Norway and other high-income countries—a development that may impact health inequalities both within and across generations [11, 12].

While a large body of research has documented the role of adult socioeconomic status in determining adult health [1, 3, 13], more recent research has focused on the importance of childhood factors for adult health. From these studies, evidence has accumulated that parental socioeconomic factors, childhood health, and residential context matters for later adult health and thus contribute to “the long arm of childhood” [14‐16]. Yet, there are several shortcomings in the current literature.

First, most studies have focused on mortality outcomes. This line of research has shown that childhood socioeconomic disadvantage—typically measured by parental education, income, or occupation—is associated with higher overall mortality. More specifically, socioeconomic disadvantage has been linked with higher mortality related to heart disease, accidents, and alcohol and substance abuse [17‐19], while the relationship with cancer is less pronounced [20]. Mortality in early adulthood is also higher among individuals who grew up in single-parent households and disadvantaged neighborhoods [14]. Adverse childhood conditions related to prenatal factors among low-SES children have also been found to predict mortality in early adulthood [21].

Although mortality differences are important, they represent a selected outcome since relatively few deaths occur in early adulthood or midlife [17, 22]. As most high-income countries face aging populations and longer life expectancies, there is also a need for more knowledge about the type of disorders for which health inequalities in early adult life are most salient, as most individuals will live long with these disorders.

Second, the existing research on morbidity in adulthood is primarily based on survey data, typically with small sample sizes, and few surveys provide reliable measures of parental socioeconomic resources throughout the entire childhood. Instead, several studies rely on retrospective accounts of childhood socioeconomic factors and often with only a few selected measures of health [23, 24]. Despite these limitations, this survey-based literature has linked low parental income, especially during early childhood, to increases in hypertension and arthritis measured in adult life [24]. Prior studies also linked low social origin to a higher risk of psychological problems, heightened levels of allostatic load [23, 25], and increased risk of poor cardiovascular health, substance abuse, musculoskeletal pain, and functional health [26‐28]. In further advancing this topic, it is important to compare the association between parental income during childhood and adult health for a broad and comprehensive set of disorders as much of the current evidence relies on a selected subset of diagnoses or self-reported conditions. Moreover, there is a need for more knowledge on whether and how the strength and shape of this relationship vary across different disorders. Previous research has found that adult health increases monotonically with current income [3], but less is known about the shape of the association between parental income in childhood and health outcomes in adulthood. For instance, whether the relationship with parental income is linear or primarily manifests itself among those growing up in low-income families, with only weak associations between parental income and adult health above a given threshold.

Parental economic resources in childhood may influence adult health directly through prenatal and childhood health [29, 30] or indirectly through socioeconomic attainments and family formation in adulthood [31, 32]. For example, it is well established that children from low-income families obtain less education and lower earnings as adults, which constitute important determinants of health [33, 34]. However, differences in childhood health between children from less advantaged families, related to factors such as prenatal conditions, poor nutrition, or various stressors, may also contribute directly to the differences in adult health. There is less knowledge about whether upward mobility in education and the labor market attenuates the gradient in adult health by parental income or whether such gradients persist regardless of improved adult attainments. To examine whether the influence of childhood socioeconomic status primarily affects adult health through socioeconomic status in adulthood requires reliable data on individuals’ completed education and adult labor market outcomes. Further, few studies have compared these direct and indirect mechanisms for more than a few selected disorders.

Table 1 shows that the study population consisted of 429,886 Norwegian individuals born in 1967–1973. Descriptive statistics are shown separately for individuals from the lowest childhood parental income decile versus everyone else, which reveal that individuals from the lowest income origins have a higher prevalence for most adult health measures; they grew up with less-educated parents and in less stable families. As adults, they had lower earnings, had less education, and were less likely to be married and have children. By contrast, overall health, which refers to whether the individuals have had at least one primary care consultation during a 5-year period, is similar across parental income groups.

In this study, we used population-wide data to obtain estimates of social gradients in health for a broad range of disorders as registered in primary and specialist health care. Further, we identified the factors related to family resources and childhood upbringing that were correlated with social gradients in health. We found that parental income in childhood is related to adult health status for a wide range of disorders. The largest absolute difference was observed for disorders related to injuries and psychological and musculoskeletal disorders, with a doubling of the risk for most of these disorders between individuals who grew up in the bottom and top vigintiles of the parental income distribution. For hypertension, diabetes, and overweight, although less common in these age groups, there was a two- to threefold increase in disorders.

The documented health gradients are substantial and particularly so given that the study population was relatively young. Not only are these individuals expected to reach older age without their health intact, but these health differences may also have consequences for work capacity and retirement decisions [38, 39]. Our results corroborate studies with smaller sample sizes and less comprehensive data that document higher risks of disorders among individuals from low socioeconomic backgrounds for several chronic disorders, such as hypertension and diabetes, and psychological disorders. However, while prior studies primarily relied on self-reported measures [40], we examine a broader range of disorders using administrative data and a longer follow-up in adulthood than previous research.

Further, our findings provide nuance into the shape of the gradient across disorders as it documents possible threshold effects. While prior studies have documented that individuals from low social origins more often have musculoskeletal disorders in adulthood, we document that there were smaller differences up to the 15th percentile for such disorders. This indicates that these disorders are more equally distributed among lower and middle parental income origins but occur less frequently among those from higher-income origins. The gradient was steeper for disorders related to back and neck pain compared to pain-related disorders such as bursitis. It is likely that some of these associations result because of occupational exposures in adulthood, where heavy manual work is more related to back and neck pain consistent with prior research [41], while bursitis might be more related to tasks in white-collar occupations such as long durations of computer use. However, factors in childhood could also partially explain these associations. For example, prior research has also shown that childhood injuries, more frequently experienced by children with low parental background, relate to higher rates of self-reported chronic pain in adulthood [28].

The risk of injuries was higher among those with low income in childhood, consistent with previous research, which has found higher mortality due to accidents among disadvantaged families [17]. We found that it decreased continuously with higher parental income with little evidence for any threshold effects. However, injuries vary in type and severity, and we might speculate that non-linear patterns would be more apparent with a more fine-grained measure. For anxiety and depression, there was evidence of non-linear associations where the differences in health by parental income were considerably steeper among those with low parental income than among those whose families were in middle or high-income groups. The risk of experiencing mental health problems was thus disproportionately concentrated among persons with the most economically deprived family backgrounds.

These documented health gradients are unlikely to reflect a difference in access to medical care as we found, as have others [41], smaller differences in the overall share of primary care consultations between individuals from high- and low-income origins. However, although access to care is universal, the quality of care may differ by socioeconomic background. For consultations related to naevus (mole) and fear of specific diseases, we found an inverse relationship where higher childhood parental income was related to more consultations. This might indicate that individuals from high-income origins engage in more preventive and risk control behavior consistent with prior research showing socioeconomic gradients in, e.g., mammogram participation and medication adherence [42, 43].

Children who grow up in low-income families face disadvantages along several additional dimensions, such as prenatal health, family instability, and low parental education [31, 44, 45]. One of our key findings was that adult health gradients by childhood parental income were persistent within different subpopulations stratified by differences in childhood circumstances (i.e., marital status and birth weight), except for parental education. This implies that parental education and correlated unobserved traits (e.g., genetic endowments and parental health) may be underlying factors that partly confound the parental income gradient in adult health.

An important aim was to assess the contribution of additional factors of childhood context as well as potential mediating factors in early adulthood. We found that childhood circumstances, including parental education, account for about 50% of the parental income gradient. In addition, we explored some of the mechanisms through which the relationship between parental income and adult health status operates. For example, adjusting for individuals’ own education, income, and family status reduced the association by about 60% for most health disorders but as much as 90% for psychological disorders. However, problems of reverse causality might be important for all adult attainments, as individuals might fare less well as adults because of health problems rather than the reverse. Such a pattern of health selection may be particularly relevant with respect to the changes after adjustments we observe for psychological disorders.

There are strengths and limitations to the approach used here. Unlike most prior research, which uses data from self-reports or hospitalizations or mortality, we relied on physician-registered health disorders, a measure that complements other measures of health. However, the validity of accurate diagnoses is a concern, as research has shown that physicians differ in their evaluation of health problems [46‐48]. For broader groups of disorders related to psychological and musculoskeletal problems, often with less specific symptoms, differences in physicians’ assessment may influence the results. Still, if there are systematic differences in the assessment of symptoms, our use of multiple health disorders should mitigate this bias. Our results are also limited to individuals who have been in contact with primary or secondary care services. If the tendency to seek medical help varies by childhood parental income, this may bias the association. Previous research has, for example, documented high rates of underdiagnosis for mental health conditions, even in countries with universal health care services [49, 50], and given the strong correlation between socioeconomic status and mental health, we may underestimate these associations. In contrast, our data do not cover private health care services. If the tendency to use the private sector is higher among high-income individuals, we might have overestimated the association. However, the use of private health care is low in Norway [10]. Finally, our sample was limited to persons who were alive and resided in Norway at the end of the observation period (i.e., at age 43). Higher mortality among persons from disadvantaged family backgrounds may lead to an underestimation of the parental income gradients in adult health, as deceased individuals, likely concentrated among those with the worst health, are not observed. However, any bias is likely to be modest, as deceased account for 3.7% of the birth cohorts covered. To what extent and in which direction outmigration may affect our results are uncertain. However, only 2.5% of non-deceased individuals in our birth cohorts lacked valid residential information at the end of the observation period.

Another caveat is related to the age of the sample. By focusing on health between ages 39 and 43, we likely capture some of the chronic diseases that begin to emerge and impair functional abilities, but we may also miss disorders with later onsets. For example, we found no relationship to respiratory disorders, which is surprising given the relation of income to smoking and physical activity [6]. However, smoking rates have drastically declined across generations implying that such factors may be less relevant for these and younger cohorts [51]. Instead, other worrisome trends have emerged, such as increases in childhood obesity [52] and higher rates of mental disorders among children and adolescents [53, 54]. How these trends will affect health disparities among the coming generations is a topic for future research. On many accounts, improved living standards and better public welfare-state services, such as high-quality childcare and universal health services, may have reduced adult health inequalities by socioeconomic family background. By contrast, increased rates of childhood poverty, a more ethnically diverse population reflecting recent immigration trends, and increased diversification of family forms (e.g., higher rates of divorce among low-income parents) may have resulted in stronger parental income gradients in health for children in more recent birth cohorts.

Finally, a limitation is that these estimates should not be interpreted as causal estimates. There could be selection effects, either through genetic or social transmission, that confound these associations. For example, parents’ poor health may both cause low parental income in childhood and poor health among offspring in adulthood, consistent with prior work on mortality, as well as other outcomes [55, 56]. Future research should focus on identifying the causal links and underlying mechanisms between childhood parental income and adult health.

We found substantial associations between childhood parental income and adult health, particularly for injuries and psychological and musculoskeletal disorders. These disorders often have a recurring trajectory and have implications for the number of years lived in good health. Our study shows that there are important intergenerational socioeconomic inequalities in health within a society with universal access to health care services. Comparative research and focused evaluation of policy reforms are needed to assess the relative effectiveness of universal health care systems in reducing severe cases of ill health and promoting health equity regardless of family background.