Key result
High-illuminance blue light is linked to reduced vagal HRV, while dim warm light may increase it.
Why the study?
Autonomic dysfunction in neuropsychiatric and sleep disorders may be modulated by light through effects on cardiac vagal activity, but evidence across healthy and clinical populations needed synthesis.
Does ocular exposure to visible light modulate vagally-mediated heart rate variability in healthy and clinical populations?
Systematic Review (n=669)
Does ocular exposure to visible light modulate vagally-mediated heart rate variability in healthy and clinical populations?
While ocular light exposure shows physiological promise for modulating autonomic function via vagally-mediated heart rate variability, high risk of bias and methodological heterogeneity currently limit its clinical application.
High risk of bias and heterogeneity limit clinical use; leaves open whether optimized light reliably modulates vagal tone.
BACKGROUND: Light therapy is increasingly used to address disorders such as depression, anxiety, sleep disturbances, and seasonal affective disorder. Autonomic dysfunction, common in these conditions, may be modulated by light through its effects on cardiac vagal activity, indexed by vagally-mediated heart rate variability (vmHRV). OBJECTIVE: This systematic review synthesized evidence on the effects of ocular exposure to visible light (illuminance and color) on vmHRV in healthy and clinical populations. METHOD: Following PRISMA guidelines, an electronic search of MEDLINE (via PubMed), Web of Science, Cochrane, and ProQuest was conducted in June 2024. Using the PICOS criteria, 24,673 records were screened, with 25 studies included. Risk of bias was assessed with the Cochrane Risk of Bias 2 tool. RESULTS: All included studies were rated as high risk of bias. High-illuminance blue light was generally associated with reduced vmHRV, likely due to its arousal-promoting effects. Conversely, lower-illuminance warm-colored light (e.g., red or dim white light) showed potential to increase vmHRV, indicating a calming effect. However, findings were inconsistent due to methodological heterogeneity, including variability in populations, exposure protocols, and control conditions. CONCLUSION: While ocular light exposure shows promise for modulating vmHRV, the high risk of bias and variability across studies limit clinical application. Future research should adopt standardized protocols, account for confounding variables, and explore long-term interventions to better evaluate light's therapeutic potential for autonomic regulation.
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Martins et al. (2025) conducted a systematic review in Healthy individuals and clinical populations (e.g., depression, anxiety) (n=669). Ocular exposure to visible light (illuminance and color) vs. Darkness, white light, or other light conditions was evaluated on Vagally-mediated heart rate variability (RMSSD and HF-HRV). High-illuminance blue light was generally associated with reduced vagally-mediated heart rate variability, whereas lower-illuminance warm-colored light showed potential to increase it.
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