Exposure to Artificial Light at Night in Relation to Weight Gain and Cardiovascular Risk among Women Cancer Survivors

Background: Cancer survivors are at high risk for weight gain and cardiovascular disease (CVD) after treatment. Artificial light at night (ALAN) may contribute to elevate risks by disrupting circadian rhythm, affecting hormonal regulation and metabolism. This relationship has not been evaluated in women cancer survivors. Methods: After excluding women with daytime sleep schedules and those with prevalent CVD, 2,401 women (aged 35-74 years) who reported a history of cancer other than non-melanoma skin cancer when they enrolled in the Sister Study (2003-2009) were followed through September 2021 (mean follow-up: 11.8 years). Self-reported indoor ALAN exposure during sleep was categorized as: no light (reference group), small nightlight in the room, light outside the room, and television/light on in the room. Generalized Poisson regression models with a log link and robust standard errors were used to estimate multivariable relative risks (RRs) for weight gain ≥5 kg and a BMI increase ≥10% over follow-up. Multivariable Cox proportional hazards models were used to estimate hazard ratios (HRs) for incident CVD, including myocardial infarction, angina, heart failure, heart bypass surgery, angioplasty, transient ischemic attack, or stroke. Results: At cohort entry, the median time since cancer diagnosis was 9.8 years and 28.6% of participants were obese (BMI ≥30). Any ALAN was associated with weight gain (RR 1.51, 95% CI 1.12-2.03) and BMI increase (RR 1.46, 95% CI 1.02-2.09). Sleeping with a television or light on was positively associated with weight gain (RR 1.83, 95% CI 1.27-2.65, P trend =0.0002), particularly in long-term survivors (>10 years, RR 2.99, 95% CI 1.71-5.23, P trend <0.0001), and with BMI increase (RR 1.89, 95% CI 1.21-2.94, P trend =0.003) over follow-up. These associations persisted after adjusting for sleep duration and quality, dietary patterns, and physical activity. Sleeping with a television or light on was also associated with increased CVD risk (HR 1.61, 95% CI 1.05-2.46, P trend =0.03), with a stronger association among survivors with pre-existing CVD risk factors (diabetes, hypertension, or dyslipidemia) at enrollment (HR 1.90, 95% CI 1.13-3.17, P trend =0.0008). Conclusions: ALAN may contribute to weight gain, higher BMI, and elevated CVD incidence in cancer survivors who are women. ALAN may be a modifiable risk factor for obesity and CVD in this high-risk population. Future studies should include an assessment of daytime light exposure.