Last week, I blogged about a study that examined personality traits and clinical variables associated with excessive exercise in eating disorder patients. In that study, 2 out of 5 participants engaged in excessive exercise. Today, I’m going to discuss a study that suggests over-exercise in disordered eating patients is associated with suicide behaviour.
Suicide rates in eating disorder patients are high. One meta-analysis suggested that out of all eating disorder related deaths, 1 in 5 are suicides. (Keep in mind, these numbers are really hard to pin down as they depend a lot on the sample population, sample size, and how the authors did their statistics, among other things.)
Another analysis found that the standardized mortality ratio (ratio of observed deaths in the study sample/expected deaths in the population of the same age but without the disease/disorder you are studying) for suicide in eating disorders was 31 for patients with anorexia nervosa and 7.5 for patients with bulimia nervosa. Moreover, around 25-35% of bulimia nervosa and 3-20% of anorexia nervosa patients attempt suicide at least once in their lifetime (Bulik et al., 1999; Corcos et al., 2002; Franko and Keel, 2006).
Clearly, understanding what sub-population of ED patients is most vulnerable to suicide ideation and suicide attempts is important to develop proper screening and treatment approaches.
In 2005, Thomas Joiner developed a theory to attempt to understand and explain suicide. The interpersonal-psychological theory of suicide (IPTS) posits that there are three essential components that must be in place before one commits suicide:
- thwarted belongingness (feelings of loneliness, perception that one has no meaningful relationships)
- perceived burdensomeness (feeling that one’s death is worth more than one’s life)
- acquired capability of suicide (ability to inflict potentially lethal self-harm which is achieved by subjecting the body to painful experiences)
The authors of the present study wanted to use the IPTS framework to examine there’s a relationship between acquired capability as a result of eating disorder behaviours and suicidal behaviour.
We were specifically interested at looking at the disordered eating behavior of over-exercise due to its noted association with pain tolerance (e.g., Ryan and Kovacic, 1966) and suicidality (e.g., Brown and Blanton, 2002), and because over-exercise often results in pain and injury (e.g., Veale, 1987; McKenzie, 1999). Behaviors such as vomiting and laxative abuse involve pain and bodily damage [...] Further, prolonged periods of restriction require one to over come hunger pains and intense discomfort. However, we hypothesized that over-exercise would be a stronger predictor of acquired capability for suicide than other compensatory behaviors.
The authors conducted four different studies to test the following ideas:
- over-exercise is associated with suicidal behaviour
- over-exercise is associated with acquired capability for suicide
- pain insensitivity mediates the relationship between over-exercise and acquired capability for suicide
- acquired capability for suicide accounts for relationship between over-exercise and suicide.
Here’s a graphic to explain their hypothesis (with the studies testing each hypothesis in brackets):
Study 1: Over-exercise was the only significant predictor of suicidal behaviours and suicide attempts in a clinical sample of bulimia nervosa patients. It was more predictive of suicidal behaviours than vomiting, dietary restraint, laxative abuse, and demographic factors such as age.
Study 2: In a sample of 171 undergraduates, over-exercise predicted the acquired capability for suicide above other eating disorder symptoms (vomiting, dietary restraint, etc.), suggesting that “over-exercise is a unique contributor to the acquired capability for suicide.”
Study 3: This study of 427 undergraduate revealed that over-exercise was related to pain insensitivity, and that pain insensitivity accounted for the relationship between over-exercise and acquired capability for suicide. Two important limitations should be noted: the authors measured pain insensitivity and not pain tolerance (which are related, but different), and they examined the relationship only at one time point, so longitudinal studies are needed to clarify whether over-exercises leads to pain insensitivity.
Study 4: In the final study, the authors found that in a sample of 512 undergraduates, acquired capability for suicide accounted for the relationship between over-exercise and suicide attempts.
The authors conclude that,
Overall, the results of four studies converge to suggest that over-exercise is related to suicide attempts through its association with pain insensitivity and acquired capability for suicide […]These results suggest that over-exercise can be hazardous to individuals not only directly—via overuse injuries—but also indirectly, via the acquired capability for suicide.
The authors caution that these results are preliminary, and prospective and longitudinal studies are needed to replicate these findings.
There are important limitations to these studies: (1) the definition of over-exercise varied between the four studies (however, the definition has also varied widely in previous studies); (2) only one study used a clinical sample (exhibiting bingeing/purging behaviour), whereas studies 2-4 used undergraduates, thus it is unclear whether the findings are generalizable to a clinical population.
I think future studies should examine if these findings hold up in clinical sample of anorexia nervosa patients as well (given than excessive exercise seems to be most prevalent among purging-type anorexia nervosa patients, see previous post), and if other aspects of the model (thwarted belongingness, perceived burdensomeness) are also related to over-exercise.
Nonetheless, the strength of this paper is that the findings from individuals studies (which had different participants) converge on the same model. If these findings are replicated, the implications are obvious. For one, screening for over-exercise might identify patients who are at a higher risk of suicide, and then treatment approaches can be tailored to work on reducing over-exercise and dealing with other factors that might feed into suicidal ideation (such as the other components of the IPTS theory).