Spending time around light at night may be linked to changes in the heart, according to a study involving more than 11,000 people.
The research appears in the European Heart Journal.
Researchers wanted to look beyond earlier studies connecting nighttime light exposure with cardiovascular disease.
They examined whether regular exposure to light after dark might also be associated with physical changes in the heart.
The study used data from 11,071 UK Biobank participants. Everyone wore a wrist-mounted light sensor for seven days, giving researchers a way to track nighttime light exposure.
Three years later, participants received cardiac MRI scans. The scans provided detailed information about the heart’s structure and how well it was working.
Researchers compared people exposed to more than three lux of light at night with those experiencing almost complete darkness.
How Nighttime Light May Change the Heart
People exposed to higher nighttime light levels were more likely to have thickening of the left ventricle wall. The left ventricle is one of the heart’s main pumping chambers.
When that wall becomes thicker, there is less room inside the chamber.
The MRI scans also suggested that the heart muscle was less flexible during each beat.
Reduced flexibility can be an early indication that the heart is not working as efficiently as it should.
Researchers also found changes involving the right ventricles and left atria.
The paper explains that these findings as evidence of cardiac remodeling, a process in which the heart’s structure and function change in response to ongoing stress or injury.
Over time, such changes can weaken the heart and contribute to heart failure.
Light Pollution and Cardiovascular Risk
The researchers say the results add to growing evidence that light pollution could be a cardiovascular risk factor.
However, the study was observational, so it does not prove that nighttime light exposure directly caused the heart changes in the participants.
So for example, maybe people who rely upon excessive nighttime lighting may also be more likely to engage in a habit that’s been clearly shown to damage the heart, such as smoking or overeating processed foods.
That said, the researchers suggest that reducing unnecessary light at night could eventually become part of strategies aimed at preventing cardiovascular disease.
A Darker Bedroom Could Help
Blackout curtains can block outdoor light, while warmer bedside lighting can reduce exposure to harsh light before or during sleep.
Small indicator lights on electronic devices should be covered.
People who work night shifts or regularly use screens after sunset may have additional sources of nighttime light to consider.
The study didn’t establish how much light is too much for an individual person, and it also didn’t show that sleeping in complete darkness will prevent cardiovascular problems.
Even so, reducing unnecessary light is relatively simple and inexpensive compared with many other approaches to improving heart health.
