Invited commentary: Body mass index and suicide--untangling an unlikely association.

A now robust series of prospective studies have found body mass index to be inversely associated with risk of completed suicide, dating back approximately 4 decades. In the progression from disturbed mental health to suicidal ideation to attempted suicide and completed suicide, augmented by impulsivity and access to highly lethal means, there are several potential steps at which body mass index has been hypothesized to lower risk. These include improved mood and self-image and reduced impulsivity, but relatively little empirical support for these exists in populations. More evidence exists to suggest that greater body weight reduces the case fatality of poisonings and shifts suicidal acts away from selected highly lethal means, such as hanging. However, in the absence of longitudinal studies with repeated measures of weight, mental health, and suicidal ideation, it remains difficult to exclude the possibility of residual confounding, particularly by psychiatric disorders that could lead to both weight loss and suicidal ideation.