We usually think about bedroom light in terms of sleep. A new study suggests it may be worth thinking about in terms of the heart, too.
The research, published in the European Heart Journal and led by Professor Lu Qi of Tulane University, followed 11,071 participants from the UK Biobank. Each person wore a wrist light sensor for seven days to measure how much light they were exposed to at night. About three years later, they had detailed cardiac MRI scans.
What the scans showed
The team compared people whose nighttime light levels went above 3 lux with people who had almost no light at night. For a sense of scale, 3 lux is dim, well below normal room lighting.
People with more nighttime light tended to have a thicker wall in the left ventricle, the heart’s main pumping chamber, which left less space inside it. Their heart muscle also appeared less able to flex normally with each beat, and changes showed up in other chambers as well.
Doctors call this kind of change “cardiac remodeling.” It is typically seen when the heart is under chronic stress, and over time it can weaken the heart. Professor Qi described the work as the first study of its kind and suggested that reducing nighttime light could be considered as one strategy for preventing heart disease.
The catch
- This is an observational study. It shows an association, not proof that light caused the heart changes. People exposed to more light at night may differ in other ways, such as shift work, stress or how well they sleep.
- Light exposure was measured for just one week, which may not reflect years of habits.
- Participants came from the UK Biobank, a large group of middle-aged and older UK adults, so the results may not apply equally to everyone.
Easy ways to darken your nights
An editorial published alongside the study argued that doctors should start asking patients how dark their bedrooms are. The advice its authors offered is inexpensive:
- Use blackout curtains or shades if streetlights or signs shine in.
- Choose warm-colored, low bedside lighting.
- Cover the small standby lights on chargers, TVs and other electronics.
- Cut back on screen use after dark.
Even if the heart findings don’t hold up in future studies, a darker bedroom is a well-established part of good sleep, so there is little downside to trying.
This article is for general information, not medical advice.