A healthy lifestyle index and its association with risk of breast, endometrial, and ovarian cancer among Canadian women

Several modifiable risk factors have been associated with risk of female cancers, but there is limited data regarding their combined effect on risk among Canadian women. Therefore, we assessed the joint association of modifiable risk factors, using a healthy lifestyle index (HLI) score, with risk of specific reproductive cancers. This study included a subcohort of 3,185 of the 39,618 women, who participated in the Canadian Study of Diet, Lifestyle, and Health, and in whom 410, 177, and 100 postmenopausal breast, endometrial, and ovarian cancers, respectively, were ascertained. We estimated hazard ratios (HR) and 95% confidence intervals (CI) using Cox proportional hazards regression models modified for the case-cohort design. Each unit increase in the HLI score was associated with 3% and 5% reductions in risk of postmenopausal breast cancer and endometrial cancer, respectively (HR 0.97; 95% CI 0.94-0.99 and HR 0.95; 95% CI 0.90-0.99, respectively). Compared to those with HLI score in the lowest category, those in the highest category had 30% and 46% reductions in risk of these cancers, respectively. The HLI score was not associated with altered risk of ovarian cancer. Our findings suggest that promoting a healthy lifestyle may aid in the primary prevention of postmenopausal breast and endometrial cancers.