This study is unique in the application of analysis of IU in Eating Disorders. The results indicate that both AN and BN are associated with heightened IU and this was associated with Harm Avoidance and Depression scores in AN and BN. In the AN group, IU was associated with Drive for Thinness and Body Dissatisfaction. In all three groups IU was associated with Trait Anxiety, and in CW, IU was associated with Drive for Thinness and also State Anxiety.
IU has received substantial attention in the anxiety literature but not yet in EDs. Studies support the notion that IU plays a role in adolescent (19
) and adult (20
) worry, and is thought to be related primarily to GAD, OCD and social anxiety (21
) as well as depression (24
). We did not find IU differences between youth and adult study participants, which supports previous research of the importance of IU elevations in both youth and adult samples (19
Both ED groups had significantly higher IU compared to CW, and ED individuals without current anxiety or depressive disorder demonstrate elevated IU compared to CW nonetheless. Furthermore, both AN and BN individuals’ IU scores correlated with Harm Avoidance and Depression scores. ED populations are consistently found to have elevated negative affect such as anxiety and depression and it is possible Harm Avoidance or depression drive IU in the ED population, in light of a lack of such a relationship in the CW. However, EDs could also be associated with primarily higher IU which could drive Harm Avoidance and depression (26
), or ED individuals might be particularly sensitive to perceptions of uncontrollability over the environment which could drive both IU and Harm Avoidance and depressive symptoms. This will need to be explored further. Norton and Mehta extended a model of vulnerabilities for emotional disorders (27
), that built on work from Clark and Watson (28
) and Taylor (30
). In that hierarchical model negative and positive affectivity influences anxiety and depressive disorder development, while anxiety sensitivity and IU are important mediators in this hierarchy.
Anxiety has been suggested to be a key vulnerability factor for the development of AN (31
), and both AN and BN have been found to have emotion regulation difficulties (32
). Thus, we believe that the development of a hierarchical model in the processing of negative and positive emotions and their impact on anxiety, mood and eating pathology would be very helpful in the conceptualization and treatment of EDs.
For the CW, IU was related to Drive for Thinness, and State and Trait Anxiety. The relationship with the anxiety measures would be consistent with the Norton model (27
), while a relationship with Drive for Thinness has not been reported before. It could be conceivable that IU is a vulnerability factor that drives even healthy females to control their body weight, maybe through the sense of heightened control. AN and BN groups showed different relationships between IU and ED related behavior. AN showed positive relationships between IU and Body Dissatisfaction as well as Drive for Thinness, but this was not the case for the BN individuals. This is consistent with our exploratory analysis indicating that IU does account for Drive for Thinness and Body Dissatisfaction to a significant degree in AN but not BN, thus demonstrating a different process occurring between eating pathology and the different EDs. Given that the model we are investigating is based on anxiety disorder research it is not surprising that the relationship between IU and eating pathology in AN would mirror the process seen in the development of anxiety disorders. Specifically, in AN, IU is associated with negative affect which may lead to the development of eating pathology. Further studies are needed to clarify this model within AN. The model however did not apply to the BN group which might be surprising. BN in contrast to AN individuals are higher in novelty seeking and may have less difficulty expressing their feelings, which could change how ED symptoms are driven by emotional states in BN. A detailed model based analysis for both AN and BN groups would go beyond the scope of this manuscript and will be developed in a subsequent article.
The correlation of IU with Trait Anxiety is consistent with the idea that IU is a trait based construct developed early in life (25
). IU does not appear to fluctuate depending on situations but rather remains stable and enduring and thus potentially contributing to a psychological vulnerability as discussed earlier in the development of anxiety (27
) and possibly EDs. State Anxiety did however relate to IU in the CW and it is possible that while State Anxiety is more environment determined as opposed to the more genetically driven Trait Anxiety (34
), during psychological wellness State and Trait Anxiety correlate well and thus both relate to IU.
The sample size was not large, and it is our plan to provide replication in an expended sample. With the assessment of ED groups with and without comorbid conditions the subgroups were reduced substantially which could have affected the results. Still, the 95% confidence intervals for the mean IUS scores in CW (44–53) were well separated from AN (68–89) and BN (59–115) without comorbid depression or anxiety disorder. The behavioral data rely on self report which could be inflated. The causal relationships between the observed behavioral variables examined in this study, if any, are not known. These aspects will need to be addressed with specific tasks that test those contingencies and in relation to brain imaging techniques. Our mean values for the IUS score in the CW was lower compared to the IUS validation studies, however those studies included individuals with higher depression and anxiety ratings most likely accounting for higher IU. This brings up a further limitation that is that we cannot distinguish illness effects on IU versus IU as a possible vulnerability for developing an ED. EDs are associated with high premorbid anxiety disorders though (2
), and with the concept that IU fuels anxiety (27
) and subsequently ED behavior, it is quite likely that IU has an important role in driving ED behavior. This will need to be addressed in longitudinal studies.
In conclusion, IU is elevated in AN and BN in this sample and may be a factor in the expression of negative affect, particularly anxiety, in these individuals and perhaps eating pathology. IU seems to be involved in ED pathology, and the perception of control should be considered in the work with the ED population since anxious individuals are characterized by their own perceptions of not being able to handle situations that are uncertain. We propose to develop models that incorporate IU, positive and negative affectivity and anxiety sensitivity in order to improve conceptualization of ED development, pathophysiology and treatment.