Night light a CVD risk factor?

A prospective cohort study using data from the UK Biobank shows that night light exposure is an important risk factor for adverse cardiovascular (CV) health.

“In this study, night light exposure was a significant risk factor for developing CV disease (CVD) among adults >40 years, [with dose-dependent associations observed],” the investigators said.

The analyses included 88,905 participants (mean age 62.4 years, 56.9 percent women). They had light data across all clock times and were free of each CV outcome at the time of light tracking. The mean time between light tracking and the final follow-up was 7.9 years.

Approximately 13 million hours of light exposure data were tracked by wrist-worn light sensors (1 week each) and categorized into the 0–50^th (darkest nights), 51^st–70^th, 71^st–90^th, and 91^st–100^th (brightest nights) percentiles. [JAMA Netw Open 2025;8:e2539031]

Compared with individuals with darkest nights, those with the brightest nights had significantly higher risks of developing coronary artery disease (CAD; adjusted hazard ratio [aHR], 1.32; p<0.001), myocardial infarction (MI; aHR, 1.47; p<0.001), heart failure (HF; aHR, 1.56; p<0.001), atrial fibrillation (AF; aHR, 1.32; p<0.001), and stroke (aHR, 1.28; p=0.009).

Participants with brighter nights (51^st–70^th and 71^st–90^th percentiles) also had higher risks of CAD (aHRs, 1.12 and 1.20, respectively), MI (aHRs, 1.20 and 1.27), and HF (aHRs, 1.15 and 1.21) than those with darkest nights.

“These associations were robust after adjusting for established CV risk factors, including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk,” said the investigators.

The correlation between brighter night light and higher CVD risks align with evidence on outdoor night light exposure. [Eur Heart J 2021;42:822-830; Stroke 2024;55:990-998; Sleep 2023;46:zsac130] “[O]ur findings are also consistent with higher CV risks observed in rotating shift workers, a population that experiences frequent exposure to bright light during the biological night,” they said.

Circadian misalignment

These associations may be attributed to the disruptive effect of night light on circadian rhythms, which can lead to dysregulation of various CV and metabolic mechanisms. [Eur J Neurosci 2020;51:531-550; J Physiol 2003;549:945-952]

Circadian disruption may promote hypercoagulability, thus increasing the risks of thromboembolic events and subsequent ischaemia. [Eur J Neurosci 2024;60:5450-5466]]

Circadian disruption may also cause higher average 24-hour blood pressure, potentially increasing the risks for vascular endothelial damage and myocardial hypertrophy. [J Biol Rhythms 2017;32:154-164; Int J Mol Sci 2023;24:9309]

Larger associations in women, younger cohorts

There were larger-magnitude associations between night light and risks of HF (p for interaction=0.006) and CAD (p for interaction=0.02) for women, and between night light and risks of HF (p for interaction=0.04) and AF (p for interaction=0.02) for younger individuals.

Evidence shows that exposure to shift work, which causes circadian disruption, predicts higher HF risk in women vs men. [Mayo Clin Proc 2022;97:1134-1144] Women’s circadian system are also apparently more sensitive to bright light than men. [J Pineal Res 2024;76:e12936] The effect in the younger cohort may be due to the attenuated circadian light sensitivity in older individuals. [Sleep 2021;44:zsaa214]

A promising new target for CVD prevention

“To our knowledge, this is the first study of personal light exposure patterns and incident CVDs, indicating night light as an important new risk factor,” the investigators noted.

Taken together, these findings suggest that night light avoidance could be a promising target for CVD prevention on top of current preventive measures, which include maintaining a healthy diet, engaging in physical activity, and avoiding alcohol and tobacco, they said.