The common sleeping mistake made by millions that puts your heart in danger

Sleeping with just a small amount of light exposure may increase your risk of heart disease, a new study suggests.

Researchers in Louisiana analyzed sleep habits and patterns of more than 11,000 people without heart disease, all of whom wore wrist sensors for a week to measure light levels throughout the night.

MRI scans performed three years later showed that people who slept with more than three lux (lumen per square meter) of light – the equivalent of bright moonlight – had thicker walls in their heart’s left ventricle.

The left ventricle is crucial for pumping oxygen-rich blood to the rest of the body, but thickened walls leave less space inside, forcing the heart to work harder and raising the risk of heart attack, rhythm disorders and stroke. 

These patients’ heart muscles were also less able to flex during a heartbeat, which researchers warn is a sign of ‘cardiac remodeling,’ or structural changes that reduce the organ’s ability to beat and sustain pressure.

The researchers estimate up to half of the impact of light on the heart was due to participants getting less sleep, about five to six hours on average.  

The extent of the damage increased in even brighter rooms, with common exposures including the glow from a smartphone, radiance from a digital alarm clock or bright lights outside. 

Researchers urged cutting out as much light pollution as possible and aiming for no more than one lux, or a very dim room lit by no more than a single candle several feet away.

‘Light pollution has emerged as a new risk factor for cardiovascular disease,’ Dr Lu Qi, senior study author and director of the Tulane University Obesity Research Center in New Orleans, said.

‘Our findings, together with evidence from other studies, suggest that reduction of nighttime light exposure should be considered as one of the potential strategies for preventing heart disease by clinicians and policy makers.’

The findings come as nearly 1 million Americans die of heart disease each year, making it the country’s leading cause of death. 

The study, published in the European Heart Journal, looked at 11,017 patients between ages 40 and 69 who were recruited from the UK Biobank database. The average age was 61, and 57 percent of participants were women. Additionally, 98 percent were white.   

For one week, each participant wore a monitor on their dominant wrist with a built-in light sensor. Of the participants, about 25 percent had no nighttime light exposure over three lux.  

About three years later, each participant underwent an MRI scan of the heart to examine its structures and functional abilities. 

The study found people exposed to at least three lux at night had greater cardiac chamber volumes in their left and right ventricles, as well as the left atrium. 

There was also greater wall mass and thickness in the left ventricle, along with greater strain on this area.

Additionally, 24 to 49 percent of the impact on the heart was due to shorter sleep duration of less than five or six hours, which Qi said it the ‘direct consequence of night light exposure.’ 

‘Night light exposure may affect other cardiovascular disease risk factors such as stress, biological changes,’ Qi added in an email to CNN.

There were several limitations to the study, such as only measuring light exposure for one week using a wrist sensor rather than measuring light exposure on the eyes. 

The researchers urged limiting nighttime light exposure to under one lux with tools such as blackout curtains and turning off hallway lights that may creep into the bedroom.