"These kinds of coping strategies are linked with increased cardiovascular reactivity to stress and higher blood pressure, so it makes sense that higher levels of maladaptive narcissism would contribute to highly reactive stress response systems and chronically elevated levels of stress."
The scientists defined narcissism as "an inflated sense of self importance, overestimation of uniqueness, and a sense of grandiosity".
While a "healthy" degree of narcissism is good for you, they say, too much can cause tension and in extreme cases lead to depression and personality disorders.
There was no relationship between healthy narcissism and cortisol in either the men or women.
But the researchers say an unhealthy form of the personality trait, reflected in exploitativeness and a sense of entitlement, appears to "chronically over-activate" the body's "HPA axis" or "stress circuit".
Signals from the brain trigger the release of hormones including cortisol from glands associated with energy expenditure, the immune system and mood change. Many anti-depressant drugs work by inhibiting activity in the HPA axis.
This work supports previous studies that have shown that while narcissistic people think they are happy and have high self-esteem, many actually display characteristics associated with unhappiness and insecurity.
The authors are not sure why this effect is not seen in women, but suggest they may conform to social stereotypes to value relationships and seek the support of others to a greater extent than men.
Professor Sara Konrath, lead author of the study, which was published in the journal PLoS ONE, said: "Narcissistic men may be paying a high price in terms of their physical health, in addition to the psychological cost to their relationships."
"Our findings suggest the HPA axis may be chronically activated in males high in unhealthy narcissism, even without an explicit stressor."
Prof Konrath hopes to conduct further research examining why narcissism is not as physiologically taxing for women.
- DAILY MAIL