Too Much Light at Night May Quietly Reshape the Heart, Study Finds

A study of more than 11,000 people has found that exposure to light at night is associated with potentially harmful changes in the structure and function of the heart. The research, led by Professor Lu Qi of Tulane University in New Orleans, was published September 9 in the European Heart Journal.

The study included 11,071 participants from the UK Biobank, each of whom wore a light sensor on their wrist for seven days to measure how much light they were exposed to at night. Three years later, the participants underwent cardiac MRI scans, which let researchers compare those exposed to nighttime light levels above 3 lux with those exposed to almost no light at all.

People exposed to higher levels of nighttime light showed thickening in the wall of the heart's left ventricle, which reduced the space inside the chamber, along with signs that the heart muscle was less able to flex normally with each heartbeat. Changes were also seen in the right ventricles and left atria. Qi said this is the first study of its kind to show that higher nighttime light exposure is linked to cardiac remodeling, a change in heart structure and function typically seen in response to chronic stress or injury that can ultimately weaken the heart and lead to heart failure.

An accompanying editorial by Professor Thomas Munzel of the University Medical Center Mainz in Germany and colleagues said clinicians treating patients with heart failure or atrial fibrillation should start asking about their sleep environment, including how dark the bedroom is and how much screen use happens after sunset. The editorial recommended simple, inexpensive measures such as blackout curtains, warm-colored bedside lighting and covering standby LEDs on household electronics, and noted that shielded fixtures, warm-spectrum bulbs and dimming streetlights are already available to reduce light pollution in cities.