Psychological attitudes and risk of breast cancer in Japan: a prospective study

Objective To examine the association between psychological factors and the risk of breast cancer prospectively in a non-Western population. Methods Data from the Japan Collaborative Cohort (JACC) study were analyzed. From 1988 to 1990, 34,497 women aged 40-79 years completed a questionnaire on medical, lifestyle and psychosocial factors. The rate ratios (RRs) of their responses were computed by fitting to proportional hazards models. Results During the mean follow-up period of 7.5 years, 149 breast cancer cases were documented. Those individuals who possessed ikigai (Japanese term meaning something that made one's life worth living) showed a significantly lower risk of breast cancer (multivariate-adjusted RR = 0.66; 95% confidence interval [CI] = 0.47-0.94). Those who perceived themselves as able to make decisions quickly also had a lower risk of breast cancer (multivariate-adjusted RR = 0.56; 95% CI = 0.36-0.87). The other factors investigated, including ease of anger arousal and self-perceived stress of daily life were not associated with breast cancer risk. Conclusions Although further studies will be necessary to verify these findings, our results suggest that having ikigai and being decisive decrease an individual's subsequent risk of breast cancer.