The goal of this study was to prospectively examine the predictors and correlates of nonsuicidal self-injury in a potentially at-risk sample and to investigate the longitudinal relationship between nonsuicidal self-injury and suicide attempt. The incidence of nonsuicidal self-injury during the follow-up period was 7.4%. Consistent with the initial hypotheses, the strongest predictors of future nonsuicidal self-injury were younger age, diagnosis of current major depression, and suicidal ideation assessed closest in time to the nonsuicidal self-injury. As hypothesized, baseline nonsuicidal self-injury was predictive of nonsuicidal self-injury during follow-up. Contrary to expectation, a history of nonsuicidal self-injury at study entry also predicted suicide attempt during follow-up, even after controlling for a history of suicide attempts; a suicide attempt after baseline also predicted nonsuicidal self-injury. While lifetime aggression severity and disruptive behavior disorders were associated with nonsuicidal self-injury in some univariate models, they did not remain significant after controlling for concomitant major depression and suicidal ideation severity. In contrast, offspring aggression severity did predict suicide attempt.
Nonsuicidal self-injury was predicted by the current diagnosis of depression and by severity of current suicidal ideation. This is consistent with the results of the cross-sectional analyses in this sample19
and with the most commonly cited motivation for nonsuicidal self-injury, which is to obtain relief from negative affect.1,5
The severity of depressive symptoms has been found in other studies to predict new or recurrent nonsuicidal self-injury; conversely, the relief of depressive symptoms is associated with a decline in the rate of nonsuicidal self-injury.8,9,12,48
While there was strong overlap between the predictors of nonsuicidal self-injury found here and those previously found for suicide attempt, there were also differences. Suicide attempt has consistently been shown to have a strong familial component, but in this study, parental history of neither nonsuicidal self-injury nor suicide attempt predicted nonsuicidal self-injury in offspring.23,47,49
This suggests that, in contrast to suicidal behavior, nonsuicidal self-injury does not display familial transmission. It is possible that recall bias may have affected these results, insofar as a single suicide attempt may have been more likely to have been recalled than a single episode of nonsuicidal self-injury. In addition, while a parental history of sexual abuse was a strong predictor of offspring attempt, it did not predict offspring nonsuicidal self-injury.24
Both parental history of attempt and history of abuse are associated with impulsive aggression in parent and child, which plays a more prominent role in the prediction of suicidal behavior than we found herein for nonsuicidal self-injury.20,23,47,50,51
Therefore, familial and personal characteristics, including abuse and impulsive aggression, contribute to the risk for suicide attempt above and beyond its shared diathesis with nonsuicidal self-injury.
Counter to expectation, baseline nonsuicidal self-injury was a strong predictor of eventual suicide attempt, even after controlling for a history of attempt. Although unexpected, this finding is convergent with other recent reports.12,13
One explanation is that nonsuicidal self-injury is a higher-frequency behavior than suicide attempt and consequently a more common manifestation of a diathesis shared by both conditions. Specifically, the annual point prevalence of medically significant nonsuicidal self-injury in adolescents may be as high as 28%, whereas only 2% of adolescents make suicide attempts that come to medical attention each year.3,5
In general, the higher the rate of psychopathology in the sample, the stronger the relationship between nonsuicidal self-injury and suicide attempt. Nonsuicidal self-injury has shown the strongest relationship to suicide attempt in clinically referred samples of severely and chronically depressed youth and those sampled from inpatients,6,12,13
with much lower rates of co-occurrence in community and nonpsychiatric samples.5,10,15
While the offspring in this study were not clinically referred, their parents often were referred for severe mood disorder, and the rate of depression among offspring is much higher than would be expected in a community sample.52
Those who engaged in nonsuicidal self-injury were younger at study entry. This may be because the incidence of nonsuicidal self-injury peaks in early adolescence to mid-adolescence.1,5
Nonsuicidal self-injury may have been a predictor of suicide attempt because nonsuicidal self-injury may be an earlier manifestation than suicide attempt of the vulnerability to mood dysregulation that serves as a potential common diathesis for both nonsuicidal self-injury and suicide attempt.53
Additional loading for personal and parental psychopathology, including impulsive aggression, might then increase the likelihood of eventual suicidal behavior. These data are consistent with the hypothesis of Joiner et al17
insofar as nonsuicidal self-injury did predict future suicide attempt, even after controlling for suicide attempt at baseline. However, we did not assess pain threshold or other constructs related to this hypothesis and so can neither confirm nor disconfirm the actual mechanism explaining the relationship between nonsuicidal self-injury and suicide attempt hypothesized by Joiner et al. One alternative explanation, that nonsuicidal self-injury may be an earlier and less severe manifestation of a shared diathesis with suicide attempt and that additional loading leads to suicide attempt, is also plausible.
This study has several limitations. The number of individuals who developed nonsuicidal self-injury or suicide attempt was small, prohibiting analyses that would have compared these 2 groups directly as well as more fine-grained analyses evaluating the severity, frequency, or patterns of occurrence of either behavior. There are also several relevant domains that were not assessed, including motivation, pain tolerance, peer influences, attributional style, and neurocognition, that may have contributed to a sharper distinction between the 2 types of behavior. The attrition rate of 30% may have resulted in losing to follow-up individuals at risk for either of these behaviors, but our sensitivity analyses support the validity of our use of imputed data. Despite these limitations, the study is one of a relatively small number of studies that prospectively examines nonsuicidal self-injury and validates hypotheses generated from cross-sectional analyses through prospective follow-up and is one of the few multi-generational studies of nonsuicidal self-injury and suicide attempt.