Chronobiology internationalJan 12, 2026

How natural and artificial light relate to body weight and key factors

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Jun 28, 2026

Abstract

Essence

In this Brazilian adult survey, more daytime natural light exposure was linked to lower BMI, while more artificial light at night was linked to higher BMI.

Evidence

A cross-sectional virtual survey of 5,260 Brazilians aged 18-65 used latent light-exposure measures, regression, and mediation analyses, finding daytime light associated with lower BMI and nighttime artificial light with higher BMI, with diet quality, bedtime, and sleep quality mediating part of the associations.

Caveat

Because this was a cross-sectional, survey-based study using self-reported behaviors and inferred light-exposure patterns, it cannot establish causality.

Simplified

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.