Burnout and cognitive impairment: Associated with serum BDNF in a Chinese Han population
Introduction
Burnout is a state of emotional, mental, and physical exhaustion caused by excessive and prolonged stress (Khamisa et al., 2015). As such, burnout among individuals who work in healthcare professions in particular has been reported to be high owing to the nature of their work (Aiken et al., 2002). The main job stressors contributing to the job stress among medical workers include death and suffering of patients, poor patients outcome, conflict with doctors, peers and patients, inadequate training, lack of social support, excessive workload and job demands, overtime and uncertainty of a treatment given to patients (Chayu and Kreitler, 2011, Garrosa et al., 2010), which are all associated with poor physical and mental health outcomes (Lambert et al., 2007). It is well documented that chronic stress affects several brain structures including the hippocampus, amygdala and prefrontal cortex. These structural changes have also been found to cause impaired memory, executive functioning and other cognitive domains (Lupien et al., 2009). Prolonged exposure to stressful working environments may lead to burnout. The main symptoms of job burnout include emotional exhaustion, physical fatigue, lack of energy, irritability, sleep disorders, difficulty in concentrating, depression, depersonalization, diminished professional accomplishment as well as cognitive deficits (Piko, 2006, Van Laethem et al., 2015). However, the pathological mechanism of burnout is not clear.
Employees with burnout frequently report cognitive problems, such as difficulties with concentration and memory (Oosterholt et al., 2016), and these self-reported cognitive problems are accompanied by actual cognitive impairments (Jonsdottir et al., 2013, Oosterholt et al., 2012; Van Dam, 2016). For example, the first study directly addressing the relationship between burnout and cognitive impairments showed impaired attention in people with high burnout (Van der Linden et al., 2003). Also, Sandstrom et al. (2005) found significant reductions in nonverbal memory and auditory and visual attention in female patients with chronic burnout compared with healthy controls, but without differences in verbal ability and verbal memory. Subsequently, some studies have demonstrated that patients with chronic stress/burnout showed impaired short-term memory tasks and reaction-time tests (Sandstrom et al., 2011), executive performance (Ohman et al., 2007, Jonsdottir et al., 2013) and working memory (Rydmark et al., 2006). Recently, several studies have investigated the longitudinal course of cognitive performance in burnout (Oosterholt et al., 2012, Beck et al., 2013, Osterberg et al., 2014). However, the results of these previous studies of the burnout-cognition are inconsistent. The most recent study showed that after 1.5-years of the initial measurement, clinical burnout patients showed a reduction of burnout symptoms and general physical and psychological complaints, but these were still elevated compared with controls. Nonetheless, they continued to report cognitive problems and still showed a minor impaired cognitive test performance (Oosterholt et al., 2016).
Brain-derived neurotrophic factor (BDNF), is a neurotrophic protein that plays a critical role in activity-dependent neuroplasticity underlying learning and memory in the hippocampus and neocortex (Lu et al., 2014). In laboratory animals, inhibition of BDNF signaling by gene knockout or antisense RNA impairs spatial learning and memory (Guzowski et al., 2000). Moreover, BDNF appears to play an important role in both early-phase long-term potentiation (LTP) and late-phase LTP (Lu et al., 2014), which is a cellular model of learning and memory. Recently, several clinical studies have demonstrated that circulating BDNF is a biomarker of memory and general cognitive function in healthy adults (Komulainen et al., 2008, Gunstad et al., 2008), schizophrenia (Zhang et al., 2012), mild cognitive impairment (Yu et al., 2008), and Alzheimer disease (Gunstad et al., 2008). Interestingly, only one previous study showed lowered serum BDNF levels in burnout group. Moreover, serum BDNF levels correlated negatively with emotional exhaustion, depersonalization, but positively with competence subscales of burnout inventory, suggesting that low BDNF might contribute to the neurobiology of burnout syndrome (Sertoz et al., 2008).
In the light of cognitive impairment and the significant changes in circulating BDNF that occurred in job burnout, and the important role of BDNF in cognition, we hypothesized that BDNF serum levels would be decreased in burnout subjects, and decreased BDNF may be associated with cognitive impairments. To our best knowledge, none has examined this association in burnout.
Section snippets
Subjects
Using a cross-sectional design, 712 healthy unrelated subjects of Chinese Han descents [aged 21–63 years, 118 men (16.6%) and 594 women (83.4%)] were recruited from a large general hospital in Beijing. All of them were from 20 clinical departments of the hospital. The participants were interviewed by trained investigators, using a detailed questionnaire including general information, socio-demographic characteristics, current and prior substance behavior, and medical and psychological history.
Demographic data
As the majority of participants were nurses, more women were selected in our study. They had the average ages of 29.9 ± 7.8 years, with average education of 15.5 ± 2.2 years. There was no significant association between BDNF levels and gender, age, education and BMI in all subjects (all p > 0.05).
Comparison between burnout and non-burnout groups
We defined “burnout” as scoring in the highest tertile of EE or DP or in the lowest tertile of PA. Based on the previous data in the Chinese population (Li et al., 2013), 23.9% of subjects scored in the
Discussion
This study had the following major findings. (1) The rate of burnout (30%) among the Chinese healthcare professionals was high; (2) serum BDNF levels were significantly decreased in burnout than non-burnout subjects; (3) burnout subjects scored lower on immediate memory, RBANS total score and attention; (4) BDNF was negatively associated with MBI total and its subscale scores, but positively with immediate memory, attention and RBANS total score; (5) mediation analysis showed that BDNF had
Declaration of conflicts of interest
All authors declare no actual or potential conflicts of interest.
Acknowledgement
Funding for this study was provided by grants from the National Natural Science Foundation of China (No 81271491 and No 81571322) to Dr Shuchang He. These sources had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.
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