Research paperImpact of childhood adversities on depression in early adulthood: A longitudinal cohort study of 478,141 individuals in Sweden
Introduction
Depression is a common and potentially debilitating disorder occurring throughout the life-course (Fleisher and Katz, 2001, Patel et al., 2007). The first onset of depression often occurs in childhood or adolescence, although treatment typically does not occur until later in life (Birmaher et al., 1996, Costello et al., 2006, Kessler et al., 2007). Depression has become one of the most common mental health conditions in medical and psychiatric practice. It ranks fourth among the leading causes of disability worldwide and is expected to become the second leading cause by 2020 (World Health Organization, 2001). Depression is one of the most common mental disorder among adolescents and young adults (Wittchen and Jacobi, 2005, World Health Organization, 2001, World Health Organization, 2016).
Several studies have pointed out childhood adversity (CA) as particularly detrimental to depression (Anda et al., 2002; Björkenstam et al., 2017; Chapman et al., 2004; Gilman et al., 2003; Gilman et al., 2002; Sareen et al., 2013; Wirback et al., 2014). Childhood adversities that have been linked to the development of depression include low family socioeconomic status, parental separation, single parenthood, parental criminality, and parental psychiatric morbidity (Anda et al., 2002, Chapman et al., 2004, Gilman et al., 2002, Sareen et al., 2013). Studies have shown that the associations between different CAs and depression vary depending on type of CA (Anda et al., 2002, Chapman et al., 2004, Gilman et al., 2002). CAs tend to occur in clusters rather than as single or separate events (Dong et al., 2004), and clustered CAs have a strong graded relationship to depression (Chapman et al., 2004, Dube et al., 2003, Green et al., 2010b).
Various pathways through which CA influences depression have been discussed, including both biological and psychological mechanisms (Swartz et al., 2017). Biological explanations suggest that CA contributes to stress-induced brain dysfunction that in turn may lead to mental health problems (Evans, 2003, Heim and Binder, 2012, Shonkoff et al., 2012; Swartz et al., 2017). Psychological explanations on the other hand suggest that CAs lead to emotional dysfunction that in turn leads to depression (Dube et al., 2003, Kovacs et al., 2008, McLaughlin et al., 2010, Shapero and Steinberg, 2013).
To date, the vast majority of existing studies has been based on self-reported information, entailing risk for recall bias (Colman et al., 2016, Hardt and Rutter, 2004, Reuben et al., 2016). One alternative approach for assessing exposure to CA is by the use of register-based data. Among others, this method eliminates the possibility of recall bias. To the best of our knowledge, few studies have used register-based data to examine associations between cumulative CA and depression (Björkenstam et al., 2017; Dahl et al., 2017). The current study adds to the literature on CA and depression by using high quality, longitudinal nationwide register data of the whole population of Sweden. In addition, although the relationship between CA and depression is widely accepted, there is little information on what proportion of depression is attributable to CA. Lastly, we use a two-step approach for identifying cases of depression: use of antidepressive medication, and having a recorded diagnosis of depression. With a cohort of approximately 480,000 individuals born between 1984 and 1988 in Sweden, the overall aim was to examine the relationship between a wide range of prospectively recorded childhood adversities and early adulthood depression. Our specific aims were to:
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investigate the differential associations between single CAs and the risk of depression
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examine the effects of cumulative CAs on later depression
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estimate the population attributable fractions (PAF) for depression attributable to CA exposure
Section snippets
Study population
The study population was defined as all individuals born in Sweden between 1984 and 1988, recorded in the Medical Birth Register, who were alive and registered in Sweden on December 31st, 2005 (n = 488,823). We applied certain exclusion criteria: owing to a high proportion of missing data on important variables, those who were adopted were excluded (n = 296), as well as those who were granted disability pension before age 23 years (n = 10,386) (mainly persons with severe learning disabilities
Results
Cohort characteristics of the study population, by sex and depression are presented in Table 2. Thirty percent of our both females and males were exposed to at least one adversity, and 10% had experienced two or more adversities. The most prevalent CA was parental separation (25%), followed by parental psychiatric morbidity (5%) and household living on public assistance (5%). Approximately 6% of the individuals received a clinical diagnosis for depression during the follow-up period (7% of
Main findings
The present study examined the association between childhood adversity and depression in young adulthood, using Swedish data on a total cohort of 478,141 individuals. Our findings show that accumulation of childhood adversity is associated with a substantial increase in the risk of depression, both in terms of a clinical diagnosis and in terms of antidepressant medication. The risk of depression grew higher with increasing number of CAs, and the risk remained after adjustment for important
Conclusion
In conclusion, this study shows that individuals with a history of exposure cumulative adversity are a high-risk group with respect to depression in young adulthood. Given that experience of CA is common, early and efficient support of disadvantaged children is of great importance for improving their long-term mental health outcomes. Sufficient evidence is already available for governments to prioritize and invest in early preventative interventions aiming to alleviate the consequences of early
Funding
This study was supported by a grant from the Swedish Council for Working Life and Social Research (grant number 2013–2729). The work of professor Vinnerljung and professor Hjern was supported by a grant from Bank of Sweden Tercentenary Foundation (grant number P10 0514). The funders had no role in the analyses interpretation of results or the writing of this manuscript.
Acknowledgements
None.
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