Does a higher educational level protect against anxiety and depression? The HUNT study☆
Introduction
A recent meta-analysis (Lorant et al., 2003) found an increased risk of depression in people belonging to the lowest socioeconomic status (SES) compared to those in the highest. However, SES is an ambiguous concept and in this meta-analysis it was represented by various characteristics such as education, income, occupation, assets, and social class. As indicators of SES, such variables are not recommended as interchangeable (Geyer, Hemström, Richard, & Vågerö, 2006). Unlike income, education is quite stable after young adulthood and is likely to result in good mental health rather than result from it. Education is a resource that is part of a person, rather than being external to the person (Ross & Mirowsky, 2006). Education precedes and influences other SES indicators, such as occupation and income. In addition, education, as a source of human capital, may enable people to succeed more generally and may prove effective in pursuing fundamental ends that include emotional well-being (Mirowsky & Ross, 1998). Education was also more frequently used than the other SES variables in the studies included in the aforementioned meta-analysis (35 out of 56) (Lorant, et al., 2003).
Furthermore, the majority (48 out of 56) of the studies (Lorant et al., 2003) had a cross-sectional design, and thereby could not demonstrate whether differences in SES were associated with increasing or decreasing differences in depression with age or time. Such changes would indicate whether the protective effect of a high SES is stable, increases, or decreases during life. Hence, the possible cumulative effect of educational level on mental health in principle can be demonstrated, by longitudinal studies but not cross-sectional ones. Four longitudinal studies that measured SES by educational level were reported in the meta-analysis (Bracke, 2000, Eaton et al., 2001, Kaplan et al., 1987, Sargeant et al., 1990). The results of these studies were inconsistent, with only one study (Kaplan et al., 1987) reporting a clear inverse association between educational level and depression. The only longitudinal study that addressed education as the main predictor of depression reported that the association was weakened and no longer statistically significant when adjusted for earlier depressive symptoms (Sargeant et al., 1990). These results imply no cumulative effect of education on depression with age. A study not included in the meta-analysis that followed adolescents into early adulthood did not show an association between educational attainment and depression at all (Miech, Caspi, Moffitt, Wright, & Silva, 1999).
Despite the limitation of the cross-sectional design in this respect, stratifying the sample by age makes it possible to study the effects of education on mental health through life. Increasing associations between low education and depression with age would imply that the protective benefits of high education accumulate through life. One study has shown that the difference in depressive level between high and low educational levels increases with age (Miech & Shanahan, 2000). Another study with a similar design has demonstrated the cumulative advantage of high educational level on physical health (Ross & Wu, 1996).
In contrast to the meta-analysis of Lorant et al. (2003), a concurrent systematic review (Fryers, Melzer, & Jenkins, 2003) addressed the relationship between social inequalities and both depression and anxiety disorders. The three relevant studies (Andrews et al., 2001, Bijl et al., 1998; Kessler et al., 1994), which were cross-sectional, all found a significant negative association between educational level and anxiety disorders. In addition, we are aware of only one longitudinal study addressing the association between anxiety and education (Miech et al., 1999). That study showed that the anxiety level was negatively associated with both the educational level of the respondent's parents and their own educational attainment.
Various studies have suggested that some mediators, such as health behaviors (smoking, alcohol consumption, and physical activity) and psycho-social status (Kaplan et al., 1987), somatic health (Kaplan et al., 1987, Miech and Shanahan, 2000), socio-demographic (Bracke, 2000, Kaplan et al., 1987) and work characteristics (Bracke, 2000, Kaplan et al., 1987, Ross and Mirowsky, 2006, Zimmerman et al., 2004) explain the association between educational level and depression. However, the data are ambiguous.
First, we used a cross-sectional design to examine whether higher educational level protects against anxiety and/or depression. Second, we examined whether such a protection accumulates or attenuates with age or time, partly by using an age stratification approach in a cross-sectional design, and partly by examining the course of anxiety and depression symptoms over an 11-year period. Third, we aimed to identify possible mediators in the relationship between education and anxiety/depression.
Section snippets
Sample
All inhabitants of Nord-Trøndelag County of Norway aged 20 years and above (N = 85,100) were invited to participate in the Nord-Trøndelag Health Study 1984–1986 (HUNT 1) (Holmen et al., 1990, HUNT, 2007), of which 77,310 individuals (90.9%) participated 11 years later in the HUNT 2 study. The HUNT 2 study consisted of all inhabitants aged 20 years and above in the same county (N = 94,197) (Holmen et al., 2003), and this time 65,648 individuals (69.7%) participated. Earlier studies have shown
Characteristics of the study samples
Primary school was the most common level of education attained in both samples (Table 1). However, educational level was characterized by a marked age gradient (Fig. 2). Hence, in the cross-sectional sample the proportion of individuals with only primary school increased monotonously from 9.3% in the youngest age group to 75.7% in the oldest. The anxiety level decreased monotonously with increasing age, while the depression level showed an exact opposite pattern (Results not shown).
Main findings
We found highly significant, though moderate, associations between low educational level and anxiety and depression in the cross-sectional as well as the longitudinal samples. The results from the cross-sectional data showed decreasing effects of education on anxiety/depression with increasing age/older cohorts. If we assume no cohort effects, this could suggest a declining protective effect over time of a higher educational level. However, there was an opposite trend in the longitudinal
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The Nord-Trøndelag Health Study (The HUNT Study) is a collaboration between The HUNT Research Centre, Faculty of Medicine, The Norwegian University of Science and Technology (NTNU), Verdal, The Norwegian Institute of Public Health, The National Health Screening Service of Norway and Nord-Trøndelag County Council.