Exposure to artificial light-at-night and cardiometabolic health: an urban perspective from the Catalan GCAT cohort study

BACKGROUND AND AIM It has been suggested that artificial light-at-night (ALAN) exposure may lead to metabolic disturbances through circadian misalignment and sleep disruption. The present study investigated associations between residential outdoor ALAN exposure and cardiometabolic risk factors and disease outcomes. METHODS We used data from 9,752 participants (59% women) in the Genomes for Life (GCAT) cohort study in Barcelona. Residential ALAN was assessed from images of the International Space Station with a 30m resolution. We estimated the visually relevant photopic illuminance and the metabolic and circadian-regulation relevant melanopic equivalent daylight (D65) illuminance, in lux. We examined cross-sectional associations between ALAN and cardiometabolic risk factors (obesity, glycaemia and hypertension). During a mean follow-up time of 2.5 years (SD 0.97) we prospectively assessed, in 5,743 participants, incident diseases (angina pectoris, myocardial infraction, stroke, diabetes, hypercholesterolemia and hypertension) ascertained through electronic health records. We adjusted our main models for demographic characteristics and further adjusted for greenness density and air pollution. RESULTS In cross-sectional analyses we found an association between photopic and melanopic Illuminances and hypertension, OR = 1.15 (95% CI 1.03-1.29) and 1.58 (1.08-2.32), per unit increase; associations remained stable after adjusting for other urban exposures. The association between illuminances and obesity was less consistent across adjustments. In incident analyses, photopic and melanopic illuminances were associated with hypercholesterolemia, OR = 1.94 (1.06-3.55) and OR = 1.30 (1.09-1.55), respectively. We had limited power, due to few incident cardiovascular events, and did not observe an association between ALAN and cardiovascular diseases nor diabetes. CONCLUSIONS The present study suggests an association between photopic and melanopic illuminance at night and risk of hypertension and hypercholesterolemia, key risk factors for cardiometabolic diseases. Results should be interpreted carefully since satellite-based ALAN assessment, even in high resolution, estimates individual exposure only partially. KEYWORDS Light-at-night, circadian misalignment, hypercholesterolemia, hypertension, cardiovascular, obesity