An extensive international cohort study has found a significant correlation between light exposure at night and an elevated risk of cardiovascular disease (CVD) in adults over the age of 50. Lead researcher Daniel P. Windred, PhD, along with his team from the Flinders Health and Medical Research Institute in Bedford Park, South Australia, concluded that minimizing nighttime light exposure could serve as an effective strategy in preventing cardiovascular diseases.
The study analyzed data from 88,905 participants, with a mean age of 62.4 years, of which 56.9% were female. The cohort was selected from approximately 502,000 individuals in the UK Biobank, recruited between 2006 and 2010. Notably, 103,669 participants used light-tracking devices on their dominant wrist for one week between 2013 and 2016, allowing researchers to capture an impressive 13 million hours of light exposure data. CVD incidents were monitored through November 2022, and the data was stratified into percentiles based on light exposure.
After adjusting for established cardiovascular risk factors such as physical activity, smoking, diet, and sleep duration, the researchers discovered that participants in the 91st-100th percentile for nighttime light exposure faced significantly higher risks of various cardiovascular conditions. For instance, the risk for coronary artery disease in this group had an adjusted hazard ratio (HR) of 1.32 (95% CI, 1.18-1.46), while the risk for myocardial infarction was 1.47 (95% CI, 1.26-1.71). The study also noted a 1.56 HR for heart failure and a 1.32 HR for atrial fibrillation.
Interestingly, the study found that female participants exhibited stronger associations between nighttime light exposure and risks for heart failure and coronary artery disease. Among younger participants, the correlation was similarly pronounced, highlighting the potential vulnerability of specific demographics to the effects of light exposure at night.
This study stands out for its focus on individual-level light exposure, as opposed to relying solely on satellite data, which has been the norm in previous research. Earlier cohort studies indicated that individuals exposed to the brightest outdoor nights had a 7%-30% increased risk of coronary heart disease and stroke when compared to those with darker nights. Windred and his colleagues emphasized that the current study provided a more accurate assessment of the impact of nighttime light on heart health.
The mechanisms through which nighttime light exposure may increase cardiovascular risk remain an area of active research. Cedernaes, MD, PhD, notes that light exposure around bedtime can disrupt the secretion of melatonin, a hormone critical for regulating sleep-wake cycles. This disruption can adversely affect circadian rhythms and health overall.
As researchers and healthcare practitioners seek to mitigate the health risks associated with nighttime light exposure, there is an increasing emphasis on identifying at-risk individuals. Family physician Juan Carlos Venis, MD, MPH, highlights the importance of discussing the health impacts of shift work with patients, particularly those with existing risk factors for heart disease. “Opening a dialogue about how their work schedule affects their health can lead to meaningful changes,” he stated.
While the findings of this study are groundbreaking, further research is needed to fully understand the relationship between light exposure, sleep timing, and cardiovascular health. As Cedernaes suggests, future studies could help determine how reducing nighttime light exposure can effectively lower the risk of cardiovascular diseases over time.
In conclusion, the evidence presented in this study underscores the importance of monitoring and managing nighttime light exposure as a potential preventive measure against cardiovascular diseases, particularly for older adults and those with existing health risks.
