Your Heart May Thank You

Any light in the bedroom at night—moonlight filling the room or light shining in from underneath a door—can increase the risk of heart disease years later by changing the heart’s structure.

Researchers from Tulane University in New Orleans analysed the impact of light during hours of sleep on a group of 11,000 volunteers who wore a light sensor on their wrist for seven days; three years later, their hearts were scanned with an MRI.

The researchers divided the group into the light levels they had been exposed to, with 3 lux being the dividing line. Three lux is equivalent to a faint illumination just after sunset but is too dark to read a book.

Those who had been exposed to more than 3 lux showed thickening in the wall of the left ventricle of the heart. The heart was less able to flex normally during each heartbeat, and this is an early sign of a malfunctioning heart.

Light exposure at bedtime is an unsuspected heart disease risk, but it can be remedied with blackout curtains, covering LED technology, such as digital alarm clocks, and making sure lights in other rooms and corridors are switched off, or at least put a door snake against the door to keep the light out.