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

Abstract

Circadian disruption may play a role in breast carcinogenesis. Previous studies reported relationships between outdoor light at night (LAN) and the breast cancer risk, but their findings are mixed. There is also a need to examine LAN and breast cancer incidence according to different individual and environmental characteristics to identify subpopulations at greater risk associated with LAN exposure. We studied residential outdoor LAN estimated from satellite imagery at baseline (1996) in relation to postmenopausal breast cancer incidence over ~16 years of follow‐up in 186 981 postmenopausal women including 12 318 incident postmenopausal breast cancer cases in the NIH‐AARP Diet and Health Study. We used Cox proportional hazards models to estimate hazard ratios (HR) and two‐sided 95% confidence intervals (CI) of the relationship between quintiles of LAN and postmenopausal breast cancer risk, overall and by hormone receptor status and cancer stage. We found that when compared to women in the lowest quintile of baseline LAN, those in the highest quintile had a 10% increase in postmenopausal breast cancer risk (HR (95% CI), 1.10 (1.02, 1.18), P‐trend, .002). The association appeared to be stronger for estrogen receptor (ER) positive breast cancer (1.12 [1.02, 1.24], .007) than for ER‐negative cancer (1.07 [0.85, 1.34], .66). Our findings also suggested that the relationship between LAN and breast cancer risk may differ by individual characteristics, such as smoking, alcohol drinking, sleep duration and BMI, and neighborhood environment. In conclusion, our study suggests that higher outdoor LAN exposure may be a risk factor for postmenopausal breast cancer.

Associations between artificial light at night and risk for thyroid cancer: A large US cohort study

“…Multiple studies have reported an association between LAN and higher risks for various chronic diseases, including cancer 29 . For example, artificial outdoor LAN assessed by satellite imagery has been linked to an increased risk of breast cancer in several large cohorts of middle‐aged to older women, including the NIH‐AARP Diet and Health Study 30,35,41 . Specifically, these studies reported that compared with women living in the lowest quintile of LAN, those in the highest quintile had an 11% to 14% increase in breast cancer risk, and the association appeared to be stronger for estrogen receptor (ER)–positive breast cancer 30 .…”

“…For example, artificial outdoor LAN assessed by satellite imagery has been linked to an increased risk of breast cancer in several large cohorts of middle‐aged to older women, including the NIH‐AARP Diet and Health Study 30,35,41 . Specifically, these studies reported that compared with women living in the lowest quintile of LAN, those in the highest quintile had an 11% to 14% increase in breast cancer risk, and the association appeared to be stronger for estrogen receptor (ER)–positive breast cancer 30 . It has been suggested that exposure to LAN reduces nighttime production of melatonin, which acts as a tumor suppressor partially through its anti‐estrogenic actions 31 .…”

“…Exposure to artificial LAN suppresses melatonin, a critical regulator of circadian rhythms, and subsequently may cause circadian disruption 27 . Multiple epidemiologic studies have reported an association between higher levels of LAN measured from satellite imagery and elevated risks for cancer, particularly breast cancer 28‐30 . It has been hypothesized that the association with breast cancer may be partially driven by melatonin's effect on estrogen pathways 31 .…”

The Association between Outdoor Artificial Light at Night and Breast Cancer Risk in Black and White Women in the Southern Community Cohort Study

“…Our findings corroborate the previously reported positive association between LAN and breast cancer risk and extend prior work by characterizing this relationship among both Blacks and Whites in a large cohort of women recruited from disadvantaged communities. Several previous cohort investigations, including in the California Teachers Study, 4 the Nurses’ Health Study II, 5 and the National Institutes of Health–AARP Diet and Health Study, 6 reported a modest increase in breast cancer risk associated with higher outdoor LAN levels (10–14%, comparing the highest to the lowest quintile). In our SCCS analysis, the effect sizes appeared larger compared with those in previous cohorts 4 , 5 , 6 although the distribution of LAN was similar and the confidence intervals overlap.…”

“… 2 , 3 Several epidemiologic studies have linked higher outdoor LAN estimated from satellite imagery to elevated incidence of breast cancer, including in cohorts predominantly comprised of White women with relatively high socioeconomic status (SES). 4 , 5 , 6 However, it remains unclear whether LAN is associated with breast cancer risk among Black women and women of lower SES.…”