Sleep

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

Longo Silva G, de Menezes R, et al. • Chronobiology international • 2026

PubMed 41524109 DOI 10.1080/07420528.2025.2606281

TL;DR

Daytime natural light exposure was associated with lower BMI and nighttime artificial light exposure was associated with higher BMI, with diet quality, sleep quality, and bedtime emerging as key mediators of these relationships.

Key Findings

Results

Daytime natural light exposure was associated with a lower BMI.

β(95%CI): -0.17(-0.28; -0.06) for the association between daytime natural light and BMI
Diet quality was the primary mediator of this association, accounting for 17% of the effect
Bedtime was the second strongest mediator, accounting for 10% of the effect
Principal Component Analysis identified daytime natural light as a latent variable comprising outdoor exposure and ambient light

Results

Nighttime artificial light exposure was associated with a higher BMI.

β(95%CI): 0.14(0.04; 0.23) for the association between nighttime artificial light and BMI
Sleep quality was the strongest mediator, accounting for 22% of the effect
Diet quality was the second strongest mediator, accounting for 16% of the effect
Nighttime artificial light was measured as a latent variable comprising light from screens and other sources

Methods

Principal Component Analysis was used to identify latent variables for both daytime natural light and nighttime artificial light exposure.

Daytime natural light was composed of two components: outdoor exposure and ambient light
Nighttime artificial light was composed of two components: light from screens and light from other sources
This approach allowed for a composite measure of light exposure rather than relying on a single indicator

Methods

The study examined multiple lifestyle mediators between light exposure and BMI.

Mediators considered included diet quality, last food intake timing, sleep quality, bedtime, and exercise
Covariates included age, sex, and education
Mediation analysis was used alongside restricted cubic splines and multivariate linear regression to evaluate associations
The virtual survey included 5,260 Brazilians aged 18-65 years, conducted from May 2023 to May 2024

Conclusions

Misaligned light exposure — disrupted from the natural day-night cycle — was associated with BMI and unhealthy lifestyle behaviors.

The findings demonstrate that both reduced daytime natural light and increased nighttime artificial light contribute to higher BMI
The effects were mediated substantially through behavioral pathways including diet quality and sleep
The authors emphasize the need to incorporate natural light alignment into obesity prevention strategies

What This Means

This research suggests that the type of light people are exposed to — and when they are exposed to it — is linked to body weight. A large survey of over 5,000 Brazilian adults found that people who got more natural light during the day tended to have a lower body mass index (BMI), while people who were exposed to more artificial light at night (such as from screens or indoor lighting) tended to have a higher BMI. These associations were not just direct; they were partly explained by differences in diet quality, sleep quality, and the timing of when people go to bed. For daytime natural light, the biggest explanatory factor was diet quality (accounting for about 17% of the link to lower BMI), followed by bedtime habits (about 10%). For nighttime artificial light, poor sleep quality was the strongest mediator (22%), with diet quality also playing a role (16%). This suggests that light exposure may influence body weight partly by shaping eating habits and sleep patterns, which are both known to affect metabolism and energy balance. This research suggests that getting adequate natural light during the day and reducing artificial light exposure at night could be important components of strategies to prevent obesity — not just through direct biological effects, but also by encouraging healthier sleep and dietary behaviors. The findings highlight light exposure as a modifiable environmental factor worth considering alongside diet and exercise in public health approaches to weight management.

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Citation

Longo Silva G, de Menezes R, de Oliveira Lima M, de Melo J, de Lima Soares L, Serenini R. (2026). Light matters: Investigating the influence of natural and artificial light on BMI and key mediators.. Chronobiology international. https://doi.org/10.1080/07420528.2025.2606281

Key Findings

What This Means

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