They then attempted to replicate this finding in a nonclinical sample of 171 college students. The students were evaluated for symptoms of bulimia nervosa, including over-exercise, as well as for "acquired capability of suicide" (that is, fearlessness about lethal self-injury). The researchers found that over-exercise predicted "acquired capability of suicide" even when other bulimia nervosa symptoms were considered.
And in a third study, this one of 467 college students, Smith and colleagues found that over-exercise predicted pain insensitivity over and above other bulimic behaviors. They thus suspect that over-exercise might lead to suicidality by increasing pain and in turn pain tolerance, and the pain tolerance in turn might make a person less fearful of death. "These results may help explain the increased rate of suicidal behavior displayed by people with bulimia nervosa," the researchers said. "And given these findings, an important treatment target for individuals with bulimia nervosa who are engaging in over-exercise may be to teach healthy exercise..."
More information about bulimia nervosa and how to treat it can be found in Psychiatric News and in American Psychiatric Publishing's Clinical Treatment of Eating Disorders.