Personality types, lifestyle, and sensitivity to mental stress in association with NK activity.

We conducted a cross-sectional study among 302 healthy Japanese male workers to make a mechanistic approach to the association between personality types and cancer; two types of personality, the emotionally unstable-introvert and the emotionally stable-extravert, were compared with each other in lifestyle, mental stress status, and biological markers such as plasma levels of neurotransmitters and NK activity of peripheral lymphocytes. We first found that emotionally unstable-introverts have a more unhealthy lifestyle associated with low NK activity than among stable-extraverts, along with higher sensitivity to mental stress (also known to suppress NK activity) than stable-extraverts. Second, emotionally unstable-introverts were found to have in fact decreased NK activity along with higher plasma levels of noradrenaline, when compared with stable-extraverts. Our results thus demonstrate that emotionally unstable-introverts have a decreased capacity of immunological host defense against cancer, which is possibly due to two factors, unhealthy lifestyle and high sensitivity to mental stress.