Artificial light that leaks into bedrooms—from screens, streetlights, or electronic devices—could be more harmful than previously thought. A new study published in JAMA Network Open and cited by RealSimple reveals that nocturnal light exposure is associated with an increased risk of heart failure and atrial fibrillation, even in people without a history of cardiovascular disease.
Researchers analyzed data from the UK Biobank, including more than 88,900 adults over 40 years of age, and found that those who slept in bright environments had a 45% to 56% higher risk of heart failure, and up to 32% more likely to suffer from arrhythmias, compared to those who slept in total darkness.
The finding confirms that the nighttime lighting environment can have profound effects on heart health, beyond rest or the aesthetics of the bedroom.
When the night stops being night
For almost ten years, participants wore light sensors that recorded light exposure between midnight and six in the morning. The results were maintained even after adjusting variables such as age, diet, socioeconomic level or physical activity. The effect was more pronounced in women and younger people, suggesting special sensitivity in these groups.
“Our findings demonstrate that, in addition to classic diet and exercise recommendations, avoiding light at night could become a new cardiovascular prevention goal,” the study authors noted.
The biological clock under attack
The main suspect is the circadian rhythm, the internal clock that regulates sleep cycles, body temperature, metabolism and blood pressure. Exposure to light—especially blue or white—during the night inhibits melatonin, the rest hormone, disrupting this biological rhythm. Over time, this imbalance can lead to increased blood pressure, inflammation, metabolic disturbances, and cardiac stress.
Links between nighttime light and increased risk of type 2 diabetes, obesity, and sleep disorders have also been documented.
How to protect your heart (and sleep)
Reducing exposure to artificial light is one of the simplest and most effective measures to protect the cardiovascular system. Specialists recommend:
Turn off screens (mobile phone, TV, computer) at least an hour before going to sleep.
Use blackout curtains or masks to block outside light.
Replace white light bulbs with warm, low-intensity lights in the bedroom.
Avoid charging your cell phone near the bed and deactivate standby lights or bright watches.
“Even small improvements sustained over time can reduce the cumulative effects of circadian imbalance,” the experts point out.
The study also looked at the protective effect of daytime sunlight. People who spent more time outdoors had a lower risk of heart disease, probably due to better regulation of the sleep-wake cycle and reduced stress. Walking or exercising early, outdoors, reinforces the circadian rhythm and improves both cardiovascular health and mental well-being.
Darkness to sleep, light to live
The final message is clear: nighttime darkness is not a luxury, but a physiological necessity. Sleeping in a really dark environment helps the body to synchronize, the heart to recover, and the mind to rest. Protecting yourself at night—from screens, streetlights, and light alarms—can be one of the simplest and most powerful decisions to take care of your heart health.
