Neurochemical effects include different variants of serotonin, unique activity rates of serotonin, and hormone imbalances.

Serotonin (5-HT) plays a role in:
- Mood regulation
- Appetite
- Impulse control

- Low serotonin function has been linked to both binge-purge behaviors and BPD symptoms such as aggression and affective instability.

- Cortisol dysregulation (HPA axis) from chronic stress or trauma may exacerbate both conditions.

Neurochemical Anomalies for Both BPD and EDs.

Both genetic and environmental factors shape personality. Twin studies suggest that approximately 40–60% of personality trait variation is heritable (Power et al., 2015). However, these findings can be influenced by shared environmental conditions in twin rearing.

Power et al. (2015) also found that neuroticism and openness are more strongly inherited within families than traits like extraversion, agreeableness, or conscientiousness. This is notable for research on Borderline Personality Disorder (BPD) and eating disorders (EDs), as neuroticism—characterized by emotional instability, anxiety, and perfectionism—is a shared trait in both.

Heritability of Personality Traits in both BPD and ED

Like many disorders, there are biological components in interplay with the environment, or past childhood experiences, that create foundations for a disorder to build from. Overlapping biological causes of BPD and EDs include the following:

- Neurochemical Effects
- Genetic Predispositions
- Neurobiological Effects

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The comorbidity is a result of the shared cognitive distress that both disorders build off of. This includes:

- Interpersonal/Environmental Effects
- Biological Effects
- Emotion Dysregulation
- Early Childhood Trauma

Additionally, eating disorders, specifically anorexia nervosa as well as bulimia nervosa tend to act as a form of coping and self-harm (symptomology) for BPD.

Causes to the Comorbidity Between Eating Disorders and Borderline Personality Disorder

Costa, J., Marôco, J., Pinto-Gouveia, J., Ferreira, C., & Castilho, P. (2016). Validation of the Psychometric Properties of the Self-Compassion Scale. Testing the Factorial Validity and Factorial Invariance of the Measure among Borderline Personality Disorder, Anxiety Disorder, Eating Disorder and General Populations. Clinical Psychology and Psychotherapy, 23(5), 460–468. https://doi.org/10.1002/cpp.1974

Bozzatello, P., Garbarini, C., Rocca, P., & Bellino, S. (2021). Borderline Personality Disorder: Risk Factors and Early Detection. Diagnostics (Basel, Switzerland), 11(11), 2142. https://doi.org/10.3390/diagnostics11112142
Khosravi, M. Eating disorders among patients with borderline personality disorder: understanding the prevalence and psychopathology. J Eat Disord 8, 38 (2020). https://doi.org/10.1186/s40337-020-00314-3

Dyson Tori, Thomas Susan J., Townsend Michelle L., Finch Adam, South Alexandra, Barkus Emma, Walter Emma, Mendonca Carley, Grenyer Brin F. S., Pickard Judy A. (2023). Salivary testosterone and cortisol levels in borderline personality disorder before and after a 12-week group dialectical behavior therapy intervention. Frontiers in Psychology, 14(14). https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2023.1195187

Federici, A. (2009). Dialectical Behaviour Therapy for the Treatment of Eating Disorders. NEDIC, NEDIC Eating Disorders Bulletin.

Lee, K. S., & Vaillancourt, T. (2024). Trajectories, comorbidity, and risk factors for adolescent disordered eating and borderline personality disorder features. Development and Psychopathology, 36(4), 1546–1557. doi:10.1017/S0954579423000792

Lee, S. S. M., Keng, S.-L., & Hong, R. Y. (2024). Validating the biosocial model of borderline personality disorder: Findings from a longitudinal study. Development and Psychopathology, 36(4), 1752–1762. doi:10.1017/S0954579423001116

Lester, R. J. (2009). Brokering Authenticity: Borderline Personality Disorder and the Ethics of Care in an American Eating Disorder Clinic. Current Anthropology, 50(3), 281–302. https://doi.org/10.1086/598782

Miller, A. E., Hotte-Meunier, A., Bain, T., Macdonald, E. P., Steiger, H., & Racine, S. E. (2025). A Qualitative Study of the Lived Treatment Experiences of Women With an Eating Disorder and Comorbid Borderline Personality Disorder. The International journal of eating disorders, 58(5), 860–867. https://doi.org/10.1002/eat.24390

Navarro-Haro, M. V., Botella, C., Guillen, V., Moliner, R., Marco, H., Jorquera, M., Baños, R., & Garcia-Palacios, A. (2018). Dialectical Behavior Therapy in the Treatment of Borderline Personality Disorder and Eating Disorders Comorbidity: A Pilot Study in a Naturalistic Setting. Cognitive Therapy and Research, 42(5), 636–649. https://doi.org/10.1007/s10608-018-9906-9

Newton, J. R. (2019). Borderline personality disorder and eating disorders: a trans-diagnostic approach to unravelling diagnostic complexity. Australasian Psychiatry : Bulletin of the Royal Australian and New Zealand College of Psychiatrists, 27(6), 556–558. https://doi.org/10.1177/1039856219852297

Ni, X., Chan, D., Chan, K., McMain, S., & Kennedy, J. L. (2009). Serotonin genes and gene–gene interactions in borderline personality disorder in a matched case-control study. Progress in Neuro-Psychopharmacology & Biological Psychiatry, 33(1), 128–133. https://doi.org/10.1016/j.pnpbp.2008.10.022.

Ntshingila, N., Poggenpoel, M., Myburgh, C. P. H., & Temane, A. (2016). Experiences of women living with borderline personality disorder. Health SA = SA Gesondheid, 21(1), 110–119. https://doi.org/10.1016/j.hsag.2016.01.001

Sansone, R. A., & Sansone, L. A. (2007). Childhood Trauma, Borderline Personality, and Eating Disorders: A Developmental Cascade. Eating Disorders, 15(4), 333–346. https://doi.org/10.1080/10640260701454345

Sansone, R. A., & Sansone, L. A. (2010). Personality Disorders as Risk Factors for Eating Disorders: Clinical Implications. Nutrition in Clinical Practice, 25(2), 116–121. https://doi.org/10.1177/0884533609357563.

Steiger, H. (2004). Eating disorders and the serotonin connection: state, trait, and developmental effects. Journal of psychiatry & neuroscience: JPN, 29(1), 20–29.

Power, R. A., & Pluess, M. (2015). Heritability estimates of the Big Five personality traits based on common genetic variants. Translational psychiatry, 5(7), e604. https://doi.org/10.1038/tp.2015.96

Reference List: Comorbidity of Borderline Personality Disorder and Eating Disorders

About 70% of those who are diagnosed with an eating disorder have experienced some type of trauma. This can include  “neglect, emotional, physical, or sexual abuse” (Newton, 2019). These types of events lead to self-harming behaviors, desire for control, emotional dysregulation, or hopelessness. All of which are common symptoms found in individuals diagnosed with BPD. Similarly, causes of BPD also tend to be sexual assault or abuse. In one study, researchers found that more than 90% of individuals with BPD reported both childhood abuse and neglect” (Sansone & Sansone, 2010).  As a result, these individuals may continue to gravitate to self-harm behaviors, whether they realize it or not, to either soothe their emotional pain or even continue what they had been accustomed to in childhood. That said, these self-harming behaviors are often impulsive and are a means to regulate the emotional instability and emptiness. That said, those with BPD might engage in purging, binging, or eating restrictions as a result of a trauma. Or those with an eating disorder may also develop more emotional dysfunction and impulsive behavior similar to that of BPD. 

Early Childhood Trauma as a Cause of BPD and ED

- Lee and Vaillancourt’s (2023) longitudinal study on the comorbidity of eating disorders and borderline personality disorder (BPD) identifies bullying as a significant environmental risk factor for the development of either or both disorders. Among 14 assessed risk factors, bullying stood out as the most potent: its elimination was projected to reduce the incidence of eating disorders by 66% and BPD by 38%.

- In addition to bullying, sociocultural and gender-based factors also play a significant role. Lee and Vaillancourt (2023) report that girls are more frequently diagnosed with eating disorders, whereas LGBTQ+ individuals are more likely to meet criteria for BPD—highlighting how identity-based vulnerabilities intersect with psychiatric risk.

- Other interpersonal contributors include personality traits such as impulsivity and emotional instability. These traits may not only predispose individuals to both conditions but also complicate diagnosis. For example, disordered eating behaviors may be misattributed to mood symptoms when in fact they are rooted in underlying personality pathology (Sansone & Sansone, 2010). Notably, these traits may arise from a complex interaction of genetic vulnerability and early relational experiences.--

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