In this study, we have demonstrated that chronic stress due to CM may leave an inflammatory mark detected in white blood cells count of patients with AN. As a matter of fact, NLR is significantly higher in patients with AN and a history of CM compared to patients with AN without history of CM. This finding is in line to what has been recently demonstrated during pregnancy in women who have experienced childhood sexual abuse [35]. In this last study, NLR was significantly higher in pregnant women with a history of childhood sexual abuse independently from prenatal depression [35]. The current medical literature points towards a role of epigenetics via DNA methylation on the HPA axis dysregulation and immune system activation after CM [36]. Besides the consistent finding of HPA axis disturbances leading to lower morning cortisol levels and a flattening of the diurnal cycle in adults with a history of CM, an accumulating body of evidence supports the fact that the immune system is chronically activated after CM [36-41]. Classically, C-reactive protein (CRP) and interleukine-6 (Il-6) have been shown to be increased in adults with CM [39-42]. However, after adjustment on age, sex, marital status and EDE-Q restriction score, the effect of CM on NLR was no more found in our sample. This demonstrates that the global effect of CM on NLR is multifactorial and that the variability of NLR in this population is related to the variability of other significant factors such as age, marital status and the level of eating restriction. As a matter of fact, NLR has already been shown to increase with age [43]. According to our data, eating restriction seems to inversely impact NLR variability. Indeed, the quality of consumed food may have an influence on NLR from one side, and eating restriction may induce cachexia and a subsequent hypercatabolic state from another side [44-47]. This might explain how eating restriction may exert a complex effect on the immune system independently from affecting the BMI. Nevertheless, the effect of eating restriction on NLR warrants to be studied in future studies. Finally, NLR seems to be influenced by the marital status with single participants being at a higher NLR than married/divorced ones. This might be in line with what has already been shown regarding the fact that being widowed, separated or never married may be accompanied with a significant modification in NLR levels [48]. This finding implicates that several lifestyle factors and behaviors related to marital statuses may explain immunologic differences, especially in patients with AN, that warrant further studying.
In our study, emotional abuse was associated with a higher NLR in the bivariate as well as in the multivariate analysis. Childhood abuse, in general, is known to be associated with loss of control on eating and depressive mood as symptoms leading to eating disorder’s psychopathology [49]. Although anxiety and depression might be the cause for inflammation in AN, this finding has not been confirmed according to available studies on the subject in the literature [50]. However, the medical literature points towards a certain role of emotional abuse as a risk factor of inflammation. In this regard, it has been demonstrated that women who reported more emotional abuse had greater percent change in CRP over time [51]. The link between emotional abuse and the psychopathology of AN may be related to the fact that patients exposed to emotional abuse may develop emotional dysregulation which inhibits the emotions of anger and disgust as a part of maladaptive attitudes [52]. In a mixed-model investigation using network analysis, the childhood emotional abuse experience has been identified as the common node mediating the association between each type of CM and eating disorder’s core symptoms [53]. In this same study, patients with AN restrictive type have shown that interoceptive awareness was included in the shortest pathway between emotional abuse and drive to thinness [53]. In the study conducted by Monteleone et al., emotional trauma in patients suffering from eating disorders contributed to the heightened cortisol production when exposed to stress [12]. Moreover, we have previously demonstrated that emotional abuse might be affecting the clinical severity of eating disorders through food addiction [10]. Accordingly, emotional abuse might be a subtype of CM determining a specific ecophenotype of maltreated patients with AN characterized, on the biological level by an increased HPA axis disturbances as well as an immune activation and on the clinical level by an increased interoceptive awareness, emotional dysregulation and food addiction. In this regard, emotional abuse as a CM may be perceived as a precursor event leading to emotional dysregulation as a coping mechanism which is a risk factor for food addiction and interoceptive awareness all of which being precipitated by HPA axis dysregulation while increasing low grade inflammation at the end of the cascade [54-56].
Although physical neglect’s subscore presented a low reliability in our study, future studies might be interested in considering it as a factor that influences the variability of NLR. Participants with physical neglect had higher NLR than those without this subtype of CM. In one study, early institutionalization interacted with stressful life events in early adolescence to predict elevated IL-6 at age 16 among individuals with prolonged institutional care. The study results are in favor of a stress-sensitizing effect of early childhood neglect [57]. According to the stress-sensitization theory, early life deprivation may enhance reactivity to stress in later life which manifests through low grade inflammation [58, 59]. An increasing amount of evidence supports the fact that early life neglect influences the child and/or adolescent’s brain development and slows down its maturation [60-63]. As with emotional abuse, we have previously demonstrated that physical neglect may increase eating disorders’ severity through food addiction possibly due to brain connectivity dysfunctions occurring early in life [12]. Accordingly, patients with AN and a history of physical neglect may become more sensible to stress from one side because of biological changes occurring to their brain and from another side because of clinical manifestations such as increased internalizing symptoms. This may result in an increased reactivity to stress later in life as manifested by a low grade inflammation and an increase in NLR.
Our study has however several limitations. First, assessments such as EDE-Q, CTQ, MINI were self-reported which might constitute a source of bias. For example, participants with more severe clinical dimensions of AN may more easily recall incidents of CM. Second, the subgroups with physical neglect and abuse have low numbers of patients which reduces the ability to generalize our findings. Third, the Cronbach’s coefficient alpha for physical neglect subtype of the CTQ shows that the participants’ answers were not consistent throughout the sample which reduces the reliability of this measure. Fourth, although multiple confounding factors have been considered in the multivariate analysis, the NLR can be affected by multiple clinical and biological determinants of AN and malnutrition so other confounding factors might have been missed in our analysis.
In conclusion, this study demonstrates that NLR is higher in patients with AN and a history of CM in general as well as in patients with AN and a history of emotional abuse in particular. The effect of CM on NLR was not present in the multivariate analysis in which age, marital status and EDE-Q restriction score seemed to influence NLR variability more significantly. However, in the multivariate analysis, emotional abuse contributed significantly to NLR’s variability. Although physical neglect significantly plays the same role, caution has been taken to withdraw conclusions from this finding due to the low reliability of its measuring tool. Future studies should focus on examining the relationship between emotional abuse as a psychopathological precursor of AN from one part and the mediators between CM and NLR variability from another. These mediators might possibly be interoceptive awareness, emotional dysregulation, eating restriction, food addiction and stress sensitization.
Strength and limits: The study demonstrates that CM in general and emotional abuse in particular may be responsible of an increase in the low grade inflammation marker NLR in AN. The study’s limitations, in addition to method’s difficulties related to measuring childhood events, can be related to the presence of clinical and biological confounding factors influencing NLR that might have been missed in our analysis.