Associations between indoor light pollution and unhealthy outcomes in 2,947 adults: Cross-sectional analysis in the HEIJO-KYO cohort

Nighttime use of artificial light is usual and essential in these modern times. Although light exposure at night (LAN) is reportedly a risk factor of several diseases, epidemiological studies on indoor LAN levels are still limited. Hence, the present study aimed to measure bedroom LAN levels by using light meters in a larger sample than in previous studies, and to evaluate the associations with comprehensive health outcomes. Out of 3012 participants, 2947 (mean age, 69.3 years; female, 60.6%) completed the bedroom LAN intensity measurement. The median bedroom LAN intensity was 1.0 lux (interquartile range, 0.2-4.0 lux). In a multivariable analysis adjusted for potential confounding factors, the highest quartile group of bedroom LAN intensity had significantly higher body weight, body mass index, abdominal circumference, and low-density lipoprotein cholesterol than the lowest quartile group. The group with a median LAN intensity ≥10 lux had significantly higher white blood cell counts and had significantly lower high-density lipoprotein cholesterol levels than the group with a median LAN intensity <10 lux. In addition, the groups with median LAN intensities ≥3 and ≥10 lux had significantly higher odds ratios for sleep disturbances and depressive symptoms than the group with <3 and <10 lux, respectively. Therefore, the present study provided real-world data on bedroom LAN levels as a marker for indoor light pollution in a large sample and suggested that higher bedroom LAN levels are significantly associated with parameters of obesity, dyslipidemia, systemic inflammation, sleep disturbances, and depressive symptoms.