Last Updated: 2003-06-03 16:51:24 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Despite the ancients' belief that melancholy can lead to cancer, new research released Tuesday suggests that your personality has no influence on whether or not you develop the disease.

Japanese researchers discovered that people who fit certain personality types -- as in people who were especially extraverted, neurotic, tough-minded or prone to lying -- were no more likely than others to develop cancer over a seven year period.

Study author Dr. Yoshitaka Tsubono of Tohoku University told Reuters Health that these findings show that people who want to reduce their risk of cancer should focus on factors that have shown to have a significant impact on the disease: namely smoking, heavy drinking, obesity and lack of exercise.

"Although further studies are needed, our results indicate that we do not have to worry about changing our personality to prevent cancer," Tsubono said.

The researcher noted that theories regarding personality's effect on the risk of cancer date back to 200 AD, but recent reports have shown mixed results, and suggested that the potential influence personality has on cancer may not be so straightforward.

"Although modern studies have been conducted since the 1960s, there have been controversies as to whether personality causes cancer, or cancer causes change in personality," Tsubono said.

To investigate the question themselves, the researchers asked 30,277 residents in Japan to complete personality tests and describe their health behaviors, then followed those residents for seven years to determine who developed cancer.

Almost 700 people were already diagnosed with cancer when the study began, and another 986 developed the disease during the following seven years.

The researchers focused on certain personality traits: extraversion, neuroticism and psychoticism -- described as liveliness, emotional instability and coldness, respectively -- as well as a trait marked by lying and social conformity.

Overall, people who had strong tendencies towards each of the four personality types were no more likely than others to develop any type of cancer, nor did they show higher risks for individual cancers -- namely, cancer of the stomach, lung, colorectum and breast.

The lack of relationship between cancer risk and personality remained even when the authors removed the influence of other factors, such as smoking, body weight and family history of cancer.

People who had a tendency towards neuroticism were more likely to have already been diagnosed with cancer before the study began, and more likely to develop cancer during the first three years of the study. However, the increased risk of cancer among overly neurotic people eventually disappeared.

Neurotic individuals are more prone to worrying and anxiety.

Writing in the Journal of the National Cancer Institute, the authors suggest that people's neuroticism may be a result of a cancer diagnosis, rather than the cause.

Early cancer may have caused some people to become more neurotic, they note, and people whose cancer was diagnosed during the first years of the study may have already had symptoms of the disease when the study began. These early symptoms, even without a diagnosis, could also have caused people to become more neurotic over time, the authors write.