Sleeping with light on may boost risk of heart disease death

Sleeping with the light on can significantly increase the risk of heart disease and death.

US and Australian scientists followed almost 90,000 Britons for nearly a decade and found that those exposed to brighter light while sleeping were significantly more likely to develop serious cardiovascular conditions.

The team warned that artificial light disrupts the body’s internal clock, known as the circadian rhythm, putting pressure on the heart over time.

Participants were given sensors worn on their wrists to measure light exposure during sleep. The researchers then compared this data to subsequent diagnoses of coronary artery disease, heart attack, heart failure, atrial fibrillation and stroke.

The findings were striking. People who were exposed to the most light at night were 56 percent more likely to have heart failure and 47 percent more likely to have a heart attack than those who slept in the dark.

They were also 32 percent more likely to have coronary artery disease and 30 percent more likely to have a stroke. Women who were exposed to higher levels of light at night faced a greater risk of coronary artery disease than men.

Writing in the journal JAMA Network Open, the researchers said: “Night light exposure was a significant risk factor for the development of cardiovascular disease in the over 40s.

“Avoiding light at night may be a useful strategy to reduce the risk of cardiovascular disease.”

Professor Frank Scheer, a neuroscientist at Brigham and Women’s Hospital in Boston and co-author of the study, said reducing light exposure was a simple but powerful step.

He added: “In the case of light exposure at night, there is no downside to keeping things dark other than using a dim light to get out of bed safely.

“If you keep the light really dim, below five lux, meaning five candles at arm’s length, you can still see your surroundings, but it will have minimal impact on your circadian system.”

Dr D., a sleep health researcher at Flinders University in Adelaide. Daniel Windred said the strength of the findings surprised even scientists.

He added: “It was surprising to see that the risk of heart failure increased by almost 60 per cent in bright night light.

“If you chronically disrupt these rhythms over a long enough period of time, you probably increase people’s risk of cardiovascular disease.”