Joint effects of multiple sleep characteristics on breast cancer progression by menopausal status

Sleep has been closely linked to breast cancer risk. However, the association between sleep and breast cancer prognosis remains unclear. The aim of this study was to evaluate the separate and joint effects of multiple sleep characteristics on breast cancer prognosis among Chinese women. A total of 1580 breast cancer patients were recruited between October 2008 and December 2014 and followed up until December 31, 2017 in Guangzhou. Multivariate Cox models were conducted to estimate the hazard ratios (HR) and 95% confidence intervals (95%CI) for breast cancer prognosis in association with sleep characteristics. Long sleep duration at night (>9 h) (HR = 2.33, 95%CI: 1.01–5.42), poor sleep quality (HR = 3.08, 95%CI: 1.74–5.47), and impaired daytime function (HR = 2.49, 95%CI: 1.65–3.79) after diagnosis were associated with an increased risk of breast cancer progression. Both short sleep duration (<6 h) (HR = 2.00, 95%CI: 1.06–3.77, P interaction = 0.011) and long sleep duration (>9 h) (HR = 4.69, 95%CI: 1.31–16.78, P interaction = 0.187) increased the progression risk only among patients with impaired but not normal daytime function. In addition, daytime napping significantly modified the effect of short sleep duration on the progression (HR = 3.55, 0.59, 95%CI: 1.55–7.97, 0.23–1.53 for patients without and with daytime napping, respectively, P interaction = 0.005). Stratification results suggested that the associations were more evident among pre-menopausal patients, although no significant interaction was observed. Our findings suggested that inadequate sleep duration to feel one's best and poor sleep quality after diagnosis were associated with an increased risk of breast cancer progression, particularly for pre-menopausal women.