Elevated depressive symptoms and adolescent injury: examining associations by injury frequency, injury type, and gender

Injury is the leading cause of death for adolescents in Canada, associated hospitalizations and emergency department visits, [1, 2] with Nova Scotia reporting higher rates of unintentional injuries relative to the rest of Canada [3]. Considerable research has gone into understanding risk and protective factors specific to injuries. Evidence has established the associations of certain social determinants with injury, [4‐6] particularly among adults, such as gender, [7‐9] socio-economic status, [7, 8, 10, 11] rural/urban living, [12] and ethnicity and culture [13, 14]. For instance, gender differences persist in injury rates with males being more likely than females to suffer serious injury, [7, 8] suggesting male risk-taking propensity and participation in contact sport are possible explanations [9, 10, 15]. Among adolescents, however, female injury rates are often higher than males, particularly for suicide and self-harm related injury [9]. Similarly, ecological studies suggest that low socioeconomic status and neighbourhood disadvantage lead to higher rates of unintentional injury hospitalization [7, 8]. Injury has also been linked with psychosocial risk factors, including alcohol and drug use [16], both of which increase the risk of unintentional (e.g. falls) and intentional injury (traffic crashes, violence and self-harm) [9, 17‐20].

Outside of suicidal behaviour (non-suicidal self-harm, suicide attempts), the role of mental health in adolescent injury has received very limited attention. Annually, in Canada, 5% of male youth and 12% of female youth, between the ages of 12 and 19, report having experienced a major depressive episode, and depression is the second highest (behind injury) hospital care expenditure among youth [21]. Student surveys from Nova Scotia have found that 20.1% of high school students showed a somewhat elevated risk of depression, with 5.9% showing very elevated depression risk [22].

There is some evidence of an association between depression and injury occurrence among adults. Depression has been linked with suicide and self-harm, [23‐25] while serious physical injury has been associated with the subsequent emergence of depression [26, 27]. Depression is also frequently comorbid with substance use [28] and conduct problems, [29] each of which increases the risk of acute injury [30, 31]. Indirectly, studies of psychological distress, which includes depression subscales, have shown mixed associations with motor vehicle collisions involvement, [32, 33] while the reciprocal link between depression and exposure to violence is quite robust [34, 35]. The extent to which depression shapes these injuries among young people and with respect to other injury events remains less clear and is an important area of inquiry.

Table 1 presents weighted demographic sample characteristics. Of the students in grades 10 to 12, about 51% were male, 14% were current smokers (17% males and 11% females) and 37% were involved in heavy drinking in the past year. Overall, 78% of high school students experienced at least one injury in the past six months, an average of 2.3 injuries, with male students reported a greater number of injuries relative to female students.

Some variation was observed by injury type. The prevalence of having at least one violence-related injury (25% for males and 12% for females) and transport-related injury (26.3% for males, 11% for females 11%) in the past six months was higher for males than females. Conversely, past six month involvement in unintentional injuries was slightly higher for female students (77.6% vs. 74.8%). Almost one-in-four students had elevated depressive symptoms, with rates for female students (31%) nearly twice that of male students (16%).

Employing the Adolescent Injury Checklist, high school students in Nova Scotia, Canada were found to have substantial injury rates, with 78% of adolescents experiencing at least one injury in the past 6 months, with an average of 2.3 injuries. One-in-four young people reported experiencing at least one intentional injury (violence-related or transport-related) in the past 6 months, while nearly three-quarters of young people were involved in at least one unintentional injury. These injury rates are substantially higher than what is observed in hospitalization data, [48], though comparable to other studies relying on self-reported injury; one key difference is that many other self-report studies focus on injury that required medical attention [10, 11, 16, 17, 49‐51]. Observed rates, both prevalence and average number of injuries, were very similar to earlier studies using the AIC from the United States and Australia [36, 39].

The main objectives of this study were to examine the association of elevated depressive symptoms with involvement in injury, and to assess the consistency of any association across injury type. Clear associations between elevated depressive symptoms and injury were observed; students with elevated depressive symptoms were more likely to have been involved in an injury the preceding six months and had, on average, experienced a greater number of injuries (approximately 40% more injuries). The association of elevated depressive symptoms with injury was also consistent across all three injury types – violence, transport, and unintentional injuries – with the strongest association for violence-related injuries. While evidence of an association with depression has previously been observed for certain injuries, particularly suicide and self-harm, [24, 25] this is the first study to report an association with a broad range of injuries, as well as total number of injuries, among young people.

How might these associations be understood? First, core symptoms of elevated depressive symptoms are poor concentration and poor sleep [52]. Cognitive studies have also shown these impairments, particularly in treatment seeking adolescents, where depressed individuals show poor executive function, attention and psychomotor skills [53]. In particular, such impairments would increase risk of unintentional and transport related injuries. However, the association between distress and subsequent motor vehicle crash has not been consistent, [32] suggesting that other explanations are likely involved. Some exposures to violence, vehicle crash or other injuries may be experienced as psychological trauma, which leads to depressive symptoms [54]. Second, elevated depressive symptoms is frequently comorbid with conduct problems [55, 56] which can increase the risk of injury, especially through unsafe driving and violence [57]. While some studies have suggested that conduct problems may lead to elevated depressive symptoms, there is also evidence that these associations may be manifestations of broader, underlying problems. Deviant peer affiliations, [58] social disadvantage and parental psychopathology [59] may lead to increases in both depression and risk-behaviours leading to injury.

Interestingly, our findings were further nuanced by gender. While elevated depressive symptoms were associated with total number of injuries and violence-related injuries, the link to transport-related injuries was present only for male adolescents, and the association with unintentional injuries was evident only for female adolescents. Gender differences appear to be a product of both differences in rates of elevated depressive symptoms between male and female students, but also injury patterns. Risky driving and resultant injuries have historically been higher in young males [60]. Young males are more likely to be involved in traffic crashes leading to injury or death, and to more-frequently partake in the risk behaviours that lead to such crashes, including impaired driving, speeding, and aggressive driving [61]. In terms of unintentional injuries, our measure captures being cut, bruised or bleeding, with a non-specific cause, and may be suggestive of self-harm related behaviours or of being the victim of intimate interpersonal violence, [62] which occurs more frequently in females. Gender differences in injury maybe also speak to the differential ways that males and females respond (externalizing or internalizing) to feelings of depression and psychiatric distress [63].

This study is not without limitations. First, it should be noted that the measure of elevated depressive symptoms relates to the previous seven days, while the injury question measures any events in the past six months. Similarly, the data is cross-sectional; as such claims of association, but not causation, can be made about the observed relationships between elevated depressive symptoms and injury. Third, the response rate for the survey was 57% and thus the generalizability of results should be interpreted with caution. While the data were weighted to provide population estimates, those at highest risk of injury and depression were likely under-represented in the survey and thus our estimates of an association are biased downward (conservative). Finally, the survey does not include other key injury determinants, including appropriate measures of socioeconomic status (i.e. family income or relative wealth) and family structure, as well as key confounders, such as impulsivity or risk taking propensity.

This study, with a representative sample of senior high school students, adds to our understanding of the role of depression in shaping adolescent injury. Interventions aimed at reducing or preventing adolescent injury should aim to modify not only the opportunities, circumstances, or environments in which injuries occur, but look to minimize the psychosocial and behaviour antecedents, such as substance use, depression and anxiety, that put adolescents at an elevated risk. Similarly, from a clinical standpoint, our findings point to a potential opportunity for primary-care physicians who treat young people for injuries to ask about feelings of depression and overall mental health.

Below are some ways that people get hurt or injured. In the past 6 months were you injured by the following (Table 7)?