Effects of light exposure on vagally-mediated heart rate variability: A systematic review

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).

This systematic review synthesized evidence on the effects of ocular exposure to visible light (illuminance and color) on vmHRV in healthy and clinical populations.

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.

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.

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.