For middle-aged adults aged 40 to 59,  examined depressive symptom trajectory classes via a latent class trajectories analysis. Four distinctive trajectory classes were found: minimal depressive symptoms, persistent-mild depressive symptoms, persistentmoderate depressive symptoms, and persistent-severe depressive symptoms. Even though the authors examined middle-aged participants, they did not explore patterns of change in depression and the sample was limited to Asians. Moreover,  examined an adult population and found that depression trajectories showed a non-linear change, however, their sample was limited to individuals living in Scotland, who are not representative of Americans . examined Americans in their sample; however, the study focused on ethnic differences in depression over time and the analysis did not reveal trajectories of depression. Hatch and colleagues (2007) used a cross-sectional approach and examined a sample of participants in England, Scotland, and Wales, and they found that economic difficulties and unemployment at 43 and/or 53 years of age were associated with greater risks of depression at 53. In addition, educational achievements by age 26 were also related to depression . Additionally, there were a couple of other studies that included a European sample. In a sample of professionally employed men in the Netherlands aged 26 to 55, researchers found that these men’s career concerns were associated with mental health problems . In a sample of Australian women aged 45 to 50, low educational attainment and unemployment were related to poor mental health . Based on these findings, the authors suggested policy changes advocating for increased support in education and employment before women reach middle adulthood .
Regarding studies that examined American middle-aged adults , examined women’s mental health in their 50s by using birth cohorts from 1931 to 1941 from a secondary data analysis of the Health and Retirement Study. Results of a cross-sectional analysis revealed that having one’s own income, owning a house, being employed, and living with a partner had an inverse relationship with depression in women’s 50s, while early childbearing and disability were positively associated with depression . Moreover , reported that having a deceased child was associated with higher depressive symptoms in late middle age (defined as 53 to 54 years of age) and early old age (64 to 65 years). In this study, the author conducted a secondary analysis of two waves from the Wisconsin Longitudinal Study, their sample included individuals born in 1939, and they analyzed the data set based on random-effects pooled time-series models . In the previous studies, socioeconomic status was consistently found as an important factor influencing mental health among middle aged adults [4,6,7]. However, these studies identified risk factors for poor mental health based on a cross-sectional approach, so that they did not provide trajectories of mental health during middle age.
On the other hand, most previous longitudinal studies looked at Europeans or Asians for their sample [1-3], and there are few empirical studies examining how trajectories of mental health change among middle aged Americans. According to , levels of depression gradually decrease during middle age. In a sample of American adults who took an initial survey and a 6-year follow-up survey, the researchers showed changes of depression across birth cohorts . For instance, changes in depression from age 30 to 36 were estimated by looking at a cohort born in 1965. Likewise, individuals born in 1959 show changes in depression from age 36 to 42; those born in 1953 from age 42 to 48; and those born in 1947 from age 48 to 54 . Results of this analysis showed that levels of depression decrease from age 30 to 42, and then begins to rise around age 42. That is, levels of depression among middle aged adults decline during their thirties , but then it begins to rise again around the forties. Overall, this study is beneficial to understand depression throughout middle age. However, the findings estimated changes in depression by combining each result from different cohorts. Therefore, it is necessary to examine trajectories of depression during middle age using one cohort based on a longitudinal approach.
Research has shown that poor mental health among middleaged adults is significantly related to economic factors, such as financial challenges and unemployment. This might be associated with the fact that by middle age, most people are participating in the labor force and earn a living for themselves. For instance, professional men in their forties presented more mental health problems, and individuals aged 36 to 45 who experienced career interruptions showed a higher prevalence of depression than those who had not. That is, economic status is one of the most important factors to understand trajectories of mental health among middleaged adults. Middle adulthood is an important age for researchers to examine as it serves as a bridge between young adulthood and older adulthood. However, few studies are available to identify trajectories of depression among middle adults, particularly for Americans. Even though some studies have examined middle aged adults’ trajectories of depression, these studies have limitations in methods and sampling as discussed. Thus, we recommend that future studies should focus on revealing trajectories of depression among middle aged adults based on longitudinal approach.
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