Healthy lifestyle index and the risk of ductal carcinoma in situ of the breast in the Women's Health Initiative.

A relatively high healthy lifestyle index (HLI) score, representing a healthy diet, participation in moderate to vigorous physical exercise, no smoking, low to no alcohol intake and a normal body mass index, has been associated with a reduced risk of invasive breast cancer. However, no study has shown an association between the HLI and the risk of ductal carcinoma in situ of the breast (DCIS), which is considered to be a nonobligate precursor of invasive breast cancer. We evaluated this association in a prospective cohort of 132 230 postmenopausal women, aged 50 to 79 years, recruited between 1993 and 1998 across the United States and enrolled in the Women's Health Initiative study. The HLI score was created and categorized into quartiles. During an average follow-up of 15.4 years, 2035 DCIS cases were ascertained. Multivariable-adjusted Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association of HLI with the risk of DCIS. Women in the highest HLI quartile had a lower DCIS risk than those in the lowest quartile (HR  = 0.80, 95% CI, 0.70-0.92) and this association was stronger in women with a family history of breast cancer (HR  = 0.70, 95% CI, 0.52-0.93), and for ER+/PR+ DCIS (HR  = 0.66, 95% CI, 0.52-0.83). These findings suggest that there is an inverse association between HLI and risk of DCIS, and suggest that the adoption of a healthy lifestyle might lower the risk of DCIS.