The prevalence of BPD was 5.9% in this general population sample, approximating values in the upper range of estimates (0.0%–5.4%) found in previous epidemiologic surveys.13–29
The discrepancy in rates of BPD between this study and others may be partly due to limitations of prior surveys with respect to unrepresentative samples and small sample sizes. Differences in diagnostic criteria, assessment instruments, and survey designs and methodologies may also have contributed to the discrepancies.
Consistent with most epidemiologic surveys,15,19,27–29
but not clinical studies,69
the prevalence of BPD did not differ by sex. Although greater rates of BPD among women in clinical studies have been attributed to increases in criterion or assessment biases, research on these biases in the clinical diagnosis of BPD has been equivocal.70, 71
Increased rates of BPD among women in clinical samples might also reflect increased treatment seeking among women with BPD, sampling biases, 72
or biological or sociocultural differences,70
explanations that have not yet been thoroughly investigated.
Despite the sex difference in BPD observed in general population and clinical samples, this study found striking similarities to recent clinical research on sex differences in rates of co-occurrence of BPD. Consistent with this research,9, 71, 73–76
the prevalences in the present study of substance use disorders, specifically alcohol dependence and any drug abuse, and narcissistic and antisocial PDs were greater among men with BPD, whereas rates of PTSD were greater among women. By contrast, previous studies found greater rates of paranoid PD among men with BPD, whereas rates in the present study were greater among women. Rates of MDD, dysthymia, panic disorder with agoraphobia, social and specific phobias, and GAD were also greater among women in this study, results not found in clinical studies. Taken together, these results are consistent with suggestions71, 76
that men with BPD manifest impulsivity through externalizing disorders. Alternatively, observed sex differences in the prevalences of Axis I and II disorders may not be associated with the diagnosis of BPD, but, rather, simply expressions of sex differences in psychopathology. Further prospective research is needed to address the role of BPD in the development of comorbidity among men and women.
studies have examined relationships between race-ethnicity and specific PDs. The absence of such data is striking,77
given that culture is so intertwined with personality, influencing world views, interpersonal relationships, communication styles, coping mechanisms, and self-concept. In contrast to 1 epidemiologic study19
that found no race-ethnic differences in the imputed rates of BPD and 1 clinical study77
that found greater rates of BPD among Hispanics, this study found greater rates of BPD among Native American men and lower rates of BPD among Hispanic men and women and Asian women. Why these minorities were found to have differential risk of BPD raises questions regarding the influence of cultural experiences, including acculturation, on personality psychopathology. Whether culturally specific experiences protect against or increase vulnerability to BPD, or whether DSM-IV PD categories are culturally uninformed, are important questions for future clinical and epidemiologic research.
BPD was inversely related to age, with the greatest decline in rates occurring after age 44 years. These findings are consistent with the McLean Study of Adult Development,78–80
a 10-year longitudinal follow-up of inpatients with BPD. At the time of the 2-year follow-up, 34.5% of patients who were 18 to 35 years old at baseline met criteria for remission; this rate increased to 49.4% at the 4-year follow-up, 68.6% at the 6-year follow-up, and 88.0% at the 10-year follow-up, when the patients were 28 to 45 years old. Consistency of the observed age gradient in the present study with the outcome of the McLean Study suggests that age differences observed in this study are, in part, real, and cannot be attributed solely to artifacts such as longer duration of illness, selective mortality, cohort effects or recall or other biases. Consistent with the clinical literature, it appears that BPD may not be as chronic as previously recognized. Further prospective epidemiological research is needed to address this issue more definitively. Determining whether remission of BPD is associated with the development of related, but different, psychopathology also appears warranted in future clinical research.
This study also identified sociodemographic characteristics associated with increased odds of BPD that were not generally reported in previous clinical and epidemiologic research due to limitations in sample size. The rates of BPD were significantly greater among individuals who were separated/divorced/widowed, and among those with low income and education, results that did not vary by sex. Whether being separated/divorced/widowed or of lower socioeconomic status represent true risk factors for BPD, or vice versa, are questions best addressed within a longitudinal framework.
At variance with most6,81–86
but not all9
clinical research, this study found that the prevalences of 12-month (59.6%) and lifetime (74.2%) anxiety disorders were similar to those of 12-month (50.9%) and lifetime (75.0%) mood disorders among individuals with BPD. The low to moderate degree of co-occurrence between BPD and anxiety disorders observed in most previous clinical research may reflect the lack of systematic study of a broad range of anxiety disorders. Further research is needed to characterize anxiety disorders more accurately among individuals with BPD, especially given the effectiveness of both pharmacologic87–94
treatments for many of the most common anxiety disorders. These results also suggest more vigilance in the assessment of anxiety disorders among individuals with BPD.
New findings in this study underscore the importance of controlling for other psychiatric disorders (that are highly comorbid with each other) when examining associations between BPD and other specific disorders.33, 34
Consistent with previous epidemiologic surveys, strong and significant associations were found between BPD and other Axis I and II disorders when sociodemographic characteristics were controlled. To understand further the unique relationships of other disorders to BPD, we additionally determined the associations controlling for all other disorders assessed in this study. Associations with bipolar I, bipolar II, and narcissistic and schizotypal PDs were reduced, but remained strong and significant. The drop in magnitude is analogous to results using twin and genetic study designs and suggests that common causal factors underlie associations between BPD and bipolar disorders and narcissistic and schizotypal PDs. However, the remaining associations remained strong after controlling for comorbidity suggesting that unique factors (e.g., genetic and/or environmental) underlie these disorder-specific associations; for example the unique factors underlying associations between BPD and bipolar I disorder are not necessarily the same as those underlying associations between BPD and schizotypal PD.
After control for additional comorbidity, significant but weaker associations remained with alcohol dependence, MDD, social phobia, GAD and PTSD among men and women. A similar pattern was observed between BPD and drug abuse, nicotine dependence, panic disorder with agoraphobia, specific phobia and paranoid, histrionic and avoidant PDs among women, and BPD and panic disorder without agoraphobia among men. Thus, while some unique disorder-specific associations were found, much of the association of BPD with these disorders appears due to factors common to these other disorders. Taken together, these findings suggest that unique and common factors may differentially contribute to disorder-specific comorbidity with BPD and that some of these associations appear to be sex-specific. These results highlight the importance of research on common and specific factors underlying the comorbidity of BPD and these disorders. Further, there is a continued need for future research to address sex differences in comorbidity with BPD.
Associations of BPD with alcohol abuse, drug dependence, dysthymia and schizoid, dependent and obsessive-compulsive PDs were no longer significant among men or women once comorbidity was controlled. These results strongly suggest that these associations sometimes observed among clinical samples were largely accounted for by other comorbid Axis I and II disorders.
That BPD was associated with a wide range of disability is consistent with the definition of BPD in the DSM-IV as well as with findings from clinical studies.97, 98
Two epidemiologic surveys99,100
that also controlled for sociodemographic characteristics, medical conditions (for physical disability measures), and Axis I disorders, found greater physical and mental disability among individuals with than among those without BPD. This study also found that disability is greater among women than men with BPD which might explain why females with BPD predominate in clinical samples. Further longitudinal research that builds upon a growing body of recent research in this area is needed to understand the impact of disability on outcome, course, and comorbidity of BPD.78, 80, 101
Potential study limitations are noted. This study is based on data from the Wave 2 NESARC. We were unable to interview respondents to the Wave 1 interview who were deceased or unable or unwilling to participate. However, the Wave 2 response rate, much higher than in most national surveys to date, combined with statistical adjustments for nonresponse at both the person and household levels on numerous sociodemographic characteristics and the presence of any lifetime Wave 1 Axis I or II disorder, considerably minimized the impact of nonresponse bias on study findings. Although we used data from the Wave 2 NESARC, the design of this study was cross-sectional, and associations may be subject to recall bias. However, data from the Wave 2 NESARC follow-up will be used to investigate further the temporal relationships between BPD and first incidence of other psychiatric disorders to confirm the observed associations.
In summary, the prevalence of BPD in the general population is greater than previously estimated from epidemiologic surveys. BPD was equally prevalent among men and women and associated with substantial mental and physical disability, especially among women. This study has also identified population subgroups at risk for BPD that have rarely been reported in previous studies. Importantly, BPD was inversely related to age, suggesting that the disorder may be less chronic than previously recognized. This study has also highlighted the need for future epidemiologic, clinical, and genetically-informed studies to identify unique and common factors underlying disorder-specific comorbidity with BPD found in the NESARC sample. Important sex differences in rates of and associations with BPD can inform more focused, hypothesis-driven investigations of those factors.