Introduction
Attention Deficit/Hyperactivity Disorder (ADHD) is a DSM-5 (American Psychiatric Association,
2013) defined neurodevelopmental disorder that is associated with a range of long term adverse outcomes, including employment and education difficulties, interpersonal problems, substance abuse, suicide and depression (Harpin,
2005; Ljung et al.,
2014; Meinzer et al.,
2014). There is strong evidence that ADHD precedes depression in a way that is consistent with a potentially causal relationship (Riglin et al.,
2020), but the mechanisms that might explain the relationship between ADHD and later depression are unclear. ADHD impacts on many aspects of a young person’s life, including functioning in social, school and home life (Harpin,
2005), that might in turn increase the risk of subsequent depression. For instance, ADHD is associated with increased difficulties in friendships (Mikami,
2010). Studies comparing children with an ADHD diagnosis to typically developing controls show that children with ADHD are likely to have fewer stable friendships (Blachman & Hinshaw,
2002; Marton et al.,
2015) and may be more likely to be friends with individuals reported as having a learning or behaviour problem (Marton et al.,
2015). Friendship difficulties such as poor quality friendships may be risk factors for subsequent depression (Goodyer et al.,
1989).
One potential explanation of the prospective association of ADHD and depression is that social stressors that commonly accompany ADHD, such as friendship difficulties, lead to an increased risk of depression (Capaldi,
1992), potentially by creating feelings of failure or lowered self-esteem (Cole,
1990; Patterson & Stoolmiller,
1991). Interpersonal stress is an important precipitator of depression, particularly during adolescence (Flynn & Rudolph,
2011) – a period when individuals spend increasing amounts of time with friends (Larson & Richards,
1991). Studies have shown that bullying (Roy et al.,
2015), social stress (Humphreys et al.,
2013) and peer-relationship difficulties (Powell et al.,
2020) contribute to the prospective relationship of ADHD and depressive symptoms in young people. However, a detailed investigation of friendship features including presence of friends, friendship quality and characteristics of the friendship group (Bukowski et al.,
1996) and how these are associated with ADHD and impact on later depression is lacking (Mikami,
2010; Mrug et al.,
2012). Important features of friendship include whether an individual has friends, the quality of these friendships including the level of companionship and closeness, as well as the characteristics of the people that an individual is friends with (Bukowski et al.,
1996). It is possible that some of these features of friendship might be more important than others in the association of ADHD and depression. For instance, a previous study conducted in secondary school children found that while retaining your best friend over time was not associated with emotional outcomes, retaining poor quality friendships over time with your top three friends was associated with subsequent emotional problems (Ng-Knight et al.,
2019). The potential role of friendships in the prospective association between ADHD and depression may also differ by sex. For example, adolescent females have been found to value aspects of friendship such as companionship more highly than males, while adolescent males have been found to value the status of their peers more highly (Hall,
2010). Identification of factors that might explain the relationship between ADHD and depression, as well as factors that moderate risk, could help pinpoint new ways of supporting young people with ADHD.
School is a key context where children make friends (Ng-Knight et al.,
2019). Classroom expectations including sustained concentration on tasks, following rules and self-regulation of emotions and behaviour may often be a poor ‘fit’ for those with ADHD, which can exacerbate poor social outcomes for this group (Richardson et al.,
2015). The transition from primary to secondary school is a period of change (Chung et al.,
1998) when good friendships can protect against poor mental health (Ng-Knight et al.,
2019), but also when there is a natural disruption to established friendships and a need to establish new ones.
In addition to friendships, it is important to consider children’s other sources of social support including parent–child relationships, which can mitigate against poor mental health outcomes in the presence of adversity (Collishaw et al.,
2016). Some research suggests a compensatory model, whereby children with low levels of warmth from peers showed better adjustment outcomes in the presence of high parental warmth compared to low parental warmth (Stocker,
1994). Warmer relationships with parents are also associated with more satisfactory friendships in young people (Deković & Meeus,
1997), and the influence of parental behaviour on the child’s friendships may be particularly important in children with ADHD (Mikami et al.,
2010). Thus, it is possible that any mediating effects of friendship in the association of ADHD and depression could be moderated by the quality of the parent–child relationship. However, parent–child relationships are often not considered in studies of ADHD and friendship (Mikami,
2010) and this is especially the case for the father-child relationship (Cabrera et al.,
2018). Investigating the influence of relationships with both mother and father is important, as they may exert differential influences on children’s friendships (Flynn et al.,
2018; Updegraff et al.,
2001). For example, a previous study found that mother supportive behaviour and hostile behaviour, and father problem-solving behaviour and hostile behaviour, influenced their adolescent children’s interaction styles with peers (Flynn et al.,
2018).
The aim of this study was to investigate which aspects of friendship (presence of friends, friendship quality and characteristics of friends) are important in increasing vulnerability to depressive symptoms in those with elevated ADHD symptoms. A secondary aim of this study was to investigate whether any indirect effects via elements of friendship were moderated by mother–child or father-child relationship quality. A follow-up exploratory research question was whether indirect effects differed according to sex. The study included children in the first year of secondary school followed over a seven-month timespan.
Discussion
To our knowledge, this is the first detailed investigation of how different aspects of friendships are involved in the prospective association of ADHD and depressive symptoms. We also investigated whether parent–child relationship quality moderated any indirect effects via friendship in the prospective association of ADHD and depressive symptoms. In a representative longitudinal study of children, ADHD symptoms were associated with children having fewer friends and lower quality friendships, which were both associated with depressive symptoms. ADHD symptoms were also associated with having a classroom friendship group that had more total difficulties, was more disruptive and less cooperative. Retaining best friendships across the study period was inversely associated with depression symptoms. These findings build upon case–control studies that found an association between ADHD and having fewer friends, more friendship conflict and aggression (Blachman & Hinshaw,
2002) and an increased likelihood of being friends with a child with a learning or behaviour problem (Marton et al.,
2015), and an association between poor friendship quality and depression (Goodyer et al.,
1989). Despite these varied associations, only friendship quality was identified as a pathway through which ADHD symptoms were associated with subsequent depressive symptoms. The indirect effect via top three friendships quality varied slightly in magnitude according to the warmth and hostility of parent–child relationships, suggesting that positive parent–child relationships might mitigate some of the adverse effects in the indirect pathway of ADHD to depressive symptoms via poor quality friendships.
The findings on friendship quality align with theories of social difficulty explaining some of the link between early psychopathology and subsequent depression (Capaldi,
1992). Our findings suggest this is also a pathway that links ADHD to depression symptoms. Friendship quality as a form of perceived social support might reduce depression risk in those with elevated ADHD symptoms via increasing a sense of connectedness and self-esteem, or by buffering against life stresses (Rueger et al.,
2016). Those with ADHD are more likely to experience adversity in various areas of life (Harpin,
2005) and good social support can mitigate against depressive outcomes in those who experience adversity (Collishaw et al.,
2016; Lee et al.,
2019). Sensitivity analyses showed that conflict and security with friends (ability to disclose problems to friend and reconcile after disagreement) appeared to be the specific elements of friendship quality that were important in the pathway from ADHD to depressive symptoms. Elevated conflict with friends has been reported for children with ADHD (Blachman & Hinshaw,
2002) and poor-quality friendships may also be risk factors for depressive outcomes in school aged children (Goodyer et al.,
1989).
Larger indirect effects via friendship quality were observed in females than males. This aligns with previous evidence of females valuing aspects of friendship quality such as companionship and intimacy more highly than males (Hall,
2010). Interpersonal stress may be more prevalent and predictive of depression in adolescent females than males (Shih et al.,
2006), particularly in females with ADHD, who may experience more peer-relationship difficulties than males with ADHD (Elkins et al.,
2011). However, it seems likely that the indirect effects observed are important to consider for both sexes.
There was some evidence of moderated mediation suggesting that indirect effects of top three friendships quality on the link between ADHD and depressive symptoms decreased slightly as self-reports of mother–child relationship warmth increased and father-child relationship hostility decreased, though the evidence for father hostility did not reach the conventional significance threshold. This draws attention to the need to consider the child’s social support across different contexts such as the parent–child relationship. Findings were suggestive of mother warmth moderating both the ADHD symptoms to friendship quality path and the friendship quality to depression symptoms path of the indirect effect. This finding is consistent with that of a previous study that found an association between parental behaviour and child peer-relationships in children with ADHD (Mikami et al.,
2010) in addition to studies that have found parent–child relationships may be able to compensate for a lack of friends (Stocker,
1994) and mitigate against poor mental health in the presence of adversity (Brennan et al.,
2003; Collishaw et al.,
2007,
2016; Lewandowski et al.,
2014). However, these moderated mediation findings should be interpreted with caution given that results were not consistent across mother and father or between warmth and hostility. Nevertheless, this may be explained in part by previous findings that suggest mothers and fathers may have differential effects on the friendships of their adolescent children (Flynn et al.,
2018; Updegraff et al.,
2001). For instance, one study found that while mother supportive behaviour and hostile behaviour influenced their children’s interactional style with peers, for fathers, it was their problem-solving behaviour and hostile behaviour that appeared to be important (Flynn et al.,
2018). Moderated mediation results in the current study were also inconsistent across the two friendship quality measures used. While some evidence of moderation by mother warmth was observed for the indirect effect via friendship quality with the top three friends, strong evidence of moderation by parent–child relationship quality was not found for the indirect effect via friendship quality with the best friend. Measurement differences in the two friendship variables used in the present study may have affected the findings, as a previous study found evidence of an interaction of friendship stability with a variable measuring quality of top three friendships, which was not found for the quality of the best friendship only (Ng-Knight et al.,
2019).
Limitations include that we relied on teacher reports of child ADHD symptoms which provide a reliable measure of ADHD symptoms in school, but most clinical research and practitioners rely primarily on parental reports of symptoms. In addition, while the SDQ hyperactivity-inattention subscale completed by teachers is a valid and useful screening tool for ADHD (Goodman,
1997), it is not a diagnostic measure and we were not able to investigate whether ADHD inattentive or hyperactive-impulsive subtypes were differentially associated with friendship or depression in this study. The inattentive subtype has been found to be the most common subtype in population samples, particularly during adolescence (Willcutt,
2012). Associations between ADHD and emotional and peer problems may vary according to subtype (Graetz et al.,
2001), and thus subtype differences are of interest for future research. Despite the longitudinal design used, there is a possibility that reverse causation contributed to observed associations. However, evidence suggests that ADHD precedes depression in a potentially causal relationship (Riglin et al.,
2020) and that the prospective relationship exists over long periods of time and when adjusting for prior emotional disorder symptomatology (Powell et al.,
2020). Moreover, a sensitivity check found that ADHD symptoms were associated with subsequent depressive symptoms when adjusting for baseline self-reported SDQ emotional problems (Goodman,
1997; Supplement
9). Although we tested indirect effects, this is not mediation analysis per se, due to exposure and mediator being measured contemporaneously (Selig & Preacher,
2009). This study had missing data, a common problem in longitudinal data (Spratt et al.,
2010). However, tests were adjusted for confounders that predicted missingness, helping to address potential bias arising from missing data (Groenwold et al.,
2012). Additionally, we conducted Multiple Imputation and results remained very similar in imputed data, suggesting bias caused by missingness was minimal (Spratt et al.,
2010). Those with ADHD may under-report their depressive symptoms and over-report their social competence, while those with depression might under-rate their social ability, which could attenuate associations (Fraser et al.,
2018; Ohan & Johnston,
2011; Whitton et al.,
2008). In addition, we were unable to investigate whether the friendships reported by the children were reciprocated in the current study, due to reported best friends not necessarily attending the same school. However, children were asked to report only their top three friendships – an approach that has been used previously (Fowler et al.,
2007; Ng-Knight et al.,
2019). Children were asked to report their best three friends rather than to report a total number of friends to capture the children’s close friendships, thereby helping to avoid some of the positive illusory bias that may affect reporting on friendships in children with ADHD symptoms. While measures of how many friends a child has in total may capture how popular or liked that individual is on a group level (e.g., in their class or school), measures that capture children’s close friendships may be more predictive of later adjustment and depression (Narr et al.,
2019; Schneider et al.,
1994). In addition, while self-rated measures of friendship presence and quality were used, peer-rated classroom data was also used to measure the characteristics of the friendship group, which also might help to mitigate against any effect of illusory biases. ADHD symptoms were associated with characteristics of the classroom friendship group (a peer-rated variable), though it did not act as a mediator of the association between ADHD and depressive symptoms in the current study.
Strengths include use of a representative school-based sample during the first year of secondary school with detailed information from multiple informants on different features of friendship, in addition to parent–child relationship quality. School life and transitions are important in adolescent mental health and may be particularly challenging for those with ADHD (Ford,
2020; Richardson et al.,
2015).
Implications of this work include pinpointing quality of friendships and parent–child relationships as important to consider clinically in those with ADHD for reducing depression risk. Many peer relationship-focused interventions, which have mainly focused on peer acceptance and social skills thus far, have shown little success in children with neurodevelopmental disorders (Mikami,
2010). Promising directions for the development of enhanced programmes include those involving a parental component focused on dyadic friendship building (Gardner et al.,
2019). Schools’ arrangements regarding awareness of friendship groups (e.g., keeping together or separating friends) are also important in ensuring children feel settled at the beginning of secondary school (Keay et al.,
2015), and may need additional consideration in children with ADHD. Practical implications for children with ADHD in mitigating later risk of emotional difficulties may also involve focusing on interventions to strengthen parent–child relationships (Abikoff et al.,
2015; Meinzer et al.,
2020). Interventions aiming to improve parent–child interactions can have beneficial effects on the mental health of both child and parent (Sonuga-Barke et al.,
2001).
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