Light matters: Investigating the influence of natural and artificial light on BMI and key mediators

This study examined the effects of daytime natural light and nighttime artificial light exposure on BMI while exploring the mediating effects of lifestyle factors. Data were drawn from a virtual survey of 5,260 Brazilians (18-65 y) conducted from May 2023-May 2024. Principal Component Analysis identified latent variables for daytime natural light (outdoor exposure and ambient light) and nighttime artificial light (from screens and other sources). Associations with BMI were evaluated using restricted cubic splines, multivariate linear regression, and mediation analysis, considering diet quality, last food intake timing, sleep quality, bedtime, exercise, age, sex, and education. Daytime light exposure was associated with a lower BMI [β(95%CI):-0.17(-0.28; -0.06)], with diet quality as the primary mediator (17%), followed by bedtime (10%). Increased exposure to artificial light at night was associated with a higher BMI [β(95%CI):0.14(0.04; 0.23)], with sleep quality (22%) and diet quality (16%) emerging as the strongest mediators. These findings demonstrate the significant impact of misaligned light exposure - disrupted from the natural day-night cycle - on BMI and its association with unhealthy lifestyle behaviors. They emphasize the need to incorporate natural light alignment into effective obesity prevention strategies.