Multicenter prospective cohort study of impact of daytime light exposure on risk of gastrointestinal cancer incidence and mortality

Daytime light exposure is essential for health, primarily by synchronizing tissue and cellular-level clocks with external light/dark cycle. Insufficient exposure may disrupt circadian alignment and contribute to adverse outcomes, including cancer. A multicenter prospective cohort study in China included 89,069 participants with objectively measured daytime light intensity and duration. Over a median follow-up of 8.8 years (804,111 person-years), 1692 gastrointestinal cancer cases were recorded, of which 891 were fatal. Higher levels of daytime light (≥1916 lux between 7:30 and 20:30, based on the 80% cutoff) were associated with lower risk of gastrointestinal cancer incidence (HR 0.87; p=0.04) and mortality (HR 0.76; p=0.008), particularly for pancreatic cancer incidence (HR 0.58; p=0.005) and mortality (HR 0.47; p=0.001). Daytime light exposure ≥ 2.4 h(≥ 5000 lux between 7:30 and 20:30, which is often used as a chronotherapeutic threshold) was associated with a lower risk of pancreatic cancer incidence and mortality. Predictive ability of daytime light metrics exceeded that of sleep quality, diet, depression, and alcohol concumption. The authors conclude that higher daytime light exposure was associated with lower risks of gastrointestinal cancer incidence and mortality, indicating a potential protective effect that warrants further investigation (graphical abstract).