Sleep characteristics, light at night and breast cancer risk in a prospective cohort

Abstract

Increasing numbers of women in the US are getting too little sleep. Inadequate sleep has been associated with impaired metabolic function and endocrine disruption. Sister Study cohort participants (n=50,884), completed baseline and follow-up questionnaires on sleep patterns. Incident breast cancers estrogen receptor (ER) status of the tumor were ascertained from questionnaires and medical records. Cox regression was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs). Analyses of sleep characteristics reported at the first follow-up interview included only participants who were breast cancer-free at time of follow-up interview. Over ~7 years of follow-up, 2,736 breast cancer cases (invasive and ductal carcinoma in situ) were diagnosed. There was little evidence that usual sleep duration or other sleep characteristics were associated with breast cancer. However, relative to those with no difficulty sleeping, women who reported having difficulty sleeping ≥ 4 nights a week were at an increased risk of overall (HR=1.32, 95% CI: 1.09–1.61) and postmenopausal breast cancer (HR=1.51, 95% CI 1.24–1.85). Risk of ER+ invasive cancer was elevated for women who reported having a light or television on in the room while sleeping (HR=1.20, 95% CI: 0.97–1.47) or who typically got less sleep than they needed to feel their best (HR=1.21, 95% CI: 0.98–1.50). In our study, most sleep characteristics, including sleep duration, were not associated with an increased risk although higher risk was observed for some markers of inadequate or poor quality sleep.

Outdoor light at night and postmenopausal breast cancer risk in the NIH‐AARP diet and health study

“…Unlike all three studies (including our study) that assessed outdoor LAN intensity using satellite imagery, two other prospective studies that instead used a questionnaire‐based LAN assessment did not find a significant association. In the Sister Study, women who reported the presence of light or television in the bedroom during sleep did not have significantly elevated risk for overall breast cancer over 7.4 years of follow up (1.09 [0.93, 1.26]) 24 . However, our study did not examine the relationship between LAN and breast cancer risk according to menopausal status.…”

“…More recently, four prospective studies investigated the associations between LAN and breast cancer risk in large cohorts. Two of these studies found a modest increase in breast cancer risk associated with outdoor LAN levels derived from satellite imagery, 22,23 while the other two studies focused on self‐reported LAN and found no or positive yet nonsignificant associations 24,25 . Findings from one study also suggested that the relationship between LAN and breast cancer may be stronger for ER‐positive (ER+) tumors, 24 supporting a role of the antiestrogen effect of melatonin in breast cancer development.…”

Association between sleep duration and breast cancer incidence: The multiethnic cohort

“…In other large population-based, predominantly white, prospective cohort studies, similar null results indicating no association between sleep duration and breast cancer were found. [20][21][22][23][24]26,34 However, a report from the Ohsaki Cohort in Japan described a higher risk of breast cancer (HR = 1.62, 95% CI: 1.05-2.50), 19 which differs from our risk estimate of 1.04 (95% CI = 0.94 to 1.14) for Japanese Americans with short sleep duration. The primarily white NIH-AARP Diet and Health Study described a lower risk of breast cancer among short sleepers (HR = 0.84, 95% CI: 0.71-0.98), which differed from our risk estimate of 1.04 (95% CI: 0.92-1.18).…”

“…In other large population‐based, predominantly white, prospective cohort studies, similar null results indicating no association between sleep duration and breast cancer were found . However, a report from the Ohsaki Cohort in Japan described a higher risk of breast cancer (HR = 1.62, 95% CI: 1.05–2.50), which differs from our risk estimate of 1.04 (95% CI = 0.94 to 1.14) for Japanese Americans with short sleep duration.…”

Light therapy and mood in breast cancer

“…Dear Editor, As found by White et al, 1 inadequate or poor quality sleep is associated with an increased risk of breast cancer. In patients, sleep can interfere immune function, alter responses to stress, and impact daytime activities and quality of life which is not only a target in the treatment of patients affected by cancer but also a predictor of response to therapy.…”