TOPLINE

People with high exposure to nighttime light had adverse remodeling in the left ventricle (LV), myocardial deformation, and impaired contractile function on cardiac MRI and had increased risks for several cardiovascular disease (CVD) events.

METHODOLOGY

• Researchers analyzed data from the UK Biobank prospective cohort to assess whether exposure to nighttime light was associated with changes in cardiac structure and function and future cardiovascular events.
• They included 11,071 adults without CVD who wore an accelerometer with a light sensor on their wrists for 7 days between 2013 and 2015. The mean age of adults was 61.1 years, and 56.6% were women.
• Nighttime for each participant was considered as their least active 5-hour window, and light above 3 lux during that period was the exposure of interest, categorized as none, low, intermediate, or high. Light above 1000 lux during the daytime and the duration of sleep were also recorded.
• Adults underwent cardiac MRI after a median duration of 3.1 years. Primary outcomes were phenotypes observed on cardiac MRI.
• For secondary outcomes, the researchers followed more than 70,000 participants for incident myocardial infarction, stroke, heart failure, atrial fibrillation, and CVD mortality over a median duration of follow-up of 7.9-9.5 years.

TAKEAWAY

• High exposure to nighttime light was associated with 2.4% greater LV mass indexed to height, 1.5% greater mean wall thickness, and 1.9% lower myocardial contraction fraction than no exposure to light above 3 lux, with a linear dose-response relationship observed across exposure levels.
• Adults with high exposure to nighttime light had 2.7% lower absolute global circumferential strain, 2.9% lower radial strain, and 2.8% lower longitudinal strain indices in the LV than those with no exposure to light above 3 lux. They also had 0.9%-2.3% larger right ventricular and left atrial volumes and a 1.1% lower left atrial ejection fraction.
• Adults with high exposure to nighttime light had a 29% higher risk for heart failure, a 15% higher risk for atrial fibrillation, a 24% higher risk for myocardial infarction, a 33% higher risk for stroke, and a 26% higher risk for CVD mortality than those with no exposure.
• A shorter duration of sleep accounted for about 24%-49% of the associations between high exposure to nighttime light and adverse cardiac MRI findings.

IN PRACTICE

"[The] findings provide mechanistic insights into how light at night may translate into increased CVD risk and underscore the importance of maintaining dark nights and adequate sleep for cardiovascular health," the researchers wrote.

SOURCE

The study was led by Jin Dai, PhD, of Tulane University in New Orleans. It was published online on September 9 in European Heart Journal.

LIMITATIONS

Researchers evaluated exposure to light for only 1 week, which may not have reflected long-term exposure. They could not assess exposure to blue light because the wrist device did not record color of light. The study was observational and could not establish that nighttime light exposure caused cardiac changes and CVD.

DISCLOSURES

The study received support from the National Heart, Lung, and Blood Institute; the National Institute of Diabetes and Digestive and Kidney Diseases; the Fogarty International Centre; and Tulane Research Centres of Excellence Awards. One author reported receiving support from one of the funding agencies and National Institute of General Medical Sciences. The authors declared having no disclosure of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.