We considered the relation between cumulative lead and dispositional pessimism and also examined the role of SES over the life course in the lead-pessimism relation. Tibia lead predicted levels of pessimism even after accounting for childhood and adult SES. Moreover, older men experiencing low childhood SES and low adult SES had higher cumulative lead levels. In addition, childhood SES and adult SES were associated with pessimism independently of each other and of lead burden. More detailed modeling revealed that lead levels are partly explained by SES and explain some of the effect of SES on pessimism. Secondary analyses considered the association of depression with lead after accounting for childhood and adult SES but did not find direct effects. Only pessimism was directly (but very strongly) associated with depression. The strong relation between pessimism and depression, together with other findings from this study, suggests that lead is an important risk for poor psychosocial outcomes net of other risk factors with which it may cluster.
There is emerging research highlighting the importance of exposures across the life course on diseases later in life. Recent evidence indicates that low childhood SES is associated with poorer health in adulthood, over and above adult SES levels (1
). Chen et al. (58
) found that, in children, low SES is associated with stress-related hormonal trajectories. These researchers hypothesized that SES may affect the way children interpret their social world. Low SES environments may be characterized by chronic stress coupled with fewer coping resources; individuals in these environments may adapt to their circumstances by being highly vigilant (59
). This coping strategy may, over time, solidify into a relatively stable attribute of expecting negative outcomes, that is, being pessimistic about the future (38
). It is interesting that there was a significant relation between childhood SES and pessimism even after accounting for adult SES and lead levels. This likely indicates other pathways by which childhood SES impacts adult cognitive orientation. It may also indicate that the developmental origins of pessimistic orientation are evident in childhood and have lasting effects into adulthood.
One explanation for the relation between SES and various mental and physical health outcomes has been the increased risk of environmental toxicant exposure with low SES status. Gump et al. (5
) found that, in children, blood lead was a significant mediator of the association between SES and vascular and hormonal responses to acute stress. There is also accumulating evidence in both human and animal studies that children in low SES environments are more vulnerable to the effects of a given level of lead (5
), which may be influenced by circumstances related to SES such as increased stress and poorer nutrition and health care (9
). For example, deficiencies in calcium or iron frequently observed in children in low SES environments can increase lead absorption and its effect on the brain (61
We found adult SES and cumulative lead to be related. Adults with low educational attainment are more likely to work in blue collar jobs that tend to have greater lead exposure and to live in lead-rich environments. In another Normative Aging Study, Elreedy et al. (63
) found a relation between individual and community-level low educational attainment and higher tibia lead levels. Also in the Normative Aging Study, Elmarsafawy et al. (42
) found that blue collar workers had on average 5.5 μg/g higher tibia lead levels. Conversely, lead in childhood may affect adult SES through its inverse relation with cognitive achievement. Worth noting is that the effect of adult SES on pessimism, although attenuated after factoring in childhood SES, was still a significant predictor of lead and pessimism. Similarly, Ek et al. (64
) found that adult achievement, independent of early relations and parental SES, was an important predictor of optimism.
As far as we know, this is the first study to investigate the association between cumulative lead and pessimism. Our findings of a positive association are congruent with findings of a relation between lead burden and depressive symptoms, particularly seen in occupational studies, which can be influenced by a pessimistic orientation (15
). In this study, we found no direct relation with depression but an indirect relation through lead’s association with pessimism, congruent with other studies finding an association between cumulative low-level lead and depression.
The etiologic mechanisms underpinning lead and emotional processing have not been fully elucidated (15
). It is not clear if psychological problems are caused directly by lead-induced brain damage or are secondary to conditions surrounding its effect on cognitive performance (61
). Poor academic performance could lead to loss of self-esteem, poor social development, and general expectation of negative outcomes (61
). However, there is some indication that lead may affect the brain systems that regulate social/emotional functioning (61
). Physiologically, lead is thought to alter the functioning of the hypothalamic-pituitary-adrenal axis either directly or indirectly, the latter mediated by inducing alterations in neurochemical function (3
). Lead may interfere with the release of neurotransmitters by mimicking or inhibiting calcium-mediated processes (3
There are some limitations to this study. Other work has found that pessimism among children predicted more parent-reported social and academic deficits (75
). Pessimism could thus have affected cognitive functioning and thereby adult social and economic position and life choices that could increase lead exposure, although including measures of child social environment mitigates some of this concern. The role of genetics (heritability) versus environment (learning) on mental health status has been a matter of debate. Pessimism is characterized as a trait (76
). Similar to other traits, it has a heritability factor of 27%, suggesting that it is also partially learned and elaborated over the life course (77
). Other research has found a graded association between optimism/pessimism and SES (22
) and patterning in optimism by changes in SES between childhood and adulthood (60
), further providing evidence that while pessimism may be relatively stable in the absence of efforts to alter it (likely in low-income environments), it can be changed where resources are available (80
). So although pessimism is characterized as a trait, it is one that is partially learned and therefore is unlikely to be fully elaborated prior to lead exposure.
Because there was little variability in depression scores (over 50% of the participants had a zero score resulting in a zero-inflation problem), we used depression as a binary variable, a more limited measure than is perhaps ideal (16
). Also, interpretation of the results may be less clear where lead is divided into quartiles and distances between quartiles tend to vary. Other limitations include the determination of childhood SES based on retrospective recollection. However, studies have shown that objective information such as parent’s education and occupation can be measured this way reliably (14
). Although we based childhood SES on a number of different factors, we did not have a measure of family income; however, we did account for homeownership, an index of wealth. In addition, it has been found that parental education and occupation are more important than family finances on outcomes such as cognitive functioning (14
). We also had limited assessment of adult SES, basing it on educational attainment, occupational category, and homeownership. Finally, this study may have limited generalizability, being a male cohort that is 97% white. Despite these limitations, this study makes an important contribution in addressing the relation among psychosocial resources, a long-term environmental exposure, and SES over the life course.
In summary, we found that higher cumulative lead was associated with higher pessimism, taking into account childhood and adult SES as well as age and health behaviors. Childhood and adult SES were negatively related to lead and associated with greater pessimism independently of each other and lead burden; adult SES was the larger contributor to pessimism. These findings suggest that lead burden and adult SES can affect pessimistic orientation and ultimately depression in later adulthood.