A certain amount of narcissism is believed to be healthy in all people, but an excessive amount results in a personality deviation known as narcissistic personality disorder (NPD). Narcissistic people attach too much importance to themselves. They consider themselves unique and precious and live perpetually focused on the fallacy of self-worship. They are considered toxic to other people because of their lack of empathy and manipulative drive, but their self-centered nature is also toxic to themselves. Research has found that this bizarre psychological condition has a neurological basis, and narcissistic men are at a greater risk of suffering from stress-related diseases.
The cortisol hormone has been found in larger quantities in men who rank higher in narcissistic traits, according to a study conducted by the University of Michigan and the University of Virginia. To reach this conclusion, researchers measured cortisol levels in 106 students through saliva samples to check the levels of psychological stress. The students were also submitted to a series of questionnaires to identify the most narcissistic personalities. Results revealed that there was a greater amount of cortisol in the saliva of the more narcissistic men, but the same did not occur in women. The authors of the study suggest that this feature could permanently hyperactivate the brain's response system to stress — the hypothalamic-pituitary-adrenal axis (HPA) — even without any particularly stressful circumstances.
Cortisol is known for its potential role in cardiovascular diseases and high blood pressure. And it has also been found to decrease bone formation, which can predispose to osteoporosis in the long-term. NPD-affected men have, therefore, greater innate health risks of suffering from health conditions associated with stress. Researchers suggest that when a narcissist's self-image is endangered, the hormone is responsible for triggering an aggressive response as a defense mechanism.
Physiological traits of narcissism are also present in the brain itself. A study, led by researcher Stephan Ropke from Charité - Universitatsmedizin Berlin, shows a structural correlation between NPD's affective deficit and a brain anomaly. With the help of MRI scans, scientists found a link between pathological narcissism and a reduction of gray matter in the region of the brain responsible for 'compassion' - the left anterior insula. This is thought to be the cause of the low empathy displayed by narcissists.
In another study, researchers found that the area of the brain responsible for impulsive behavior management was more active than normal in narcissists. This predisposes them to poor decision-making, which may get them in unnecessarily risky or dangerous situations.