Sleeping with the lights on may elevate your risk of heart attack.

The human organism was shaped to the rhythm of the Sun, based on the regular alternation between light and darkness. This cycle, which has remained unchanged for millennia, is now fragmented by artificial light sources which extend the day indefinitely. Far from being harmless, this progressive intrusion disrupts the most fundamental balances. This is precisely what a series of recent studies reveals, highlighting the unsuspected effects of nighttime light on the heart and sleep.

The day that invites itself into our nights

Every evening, a faint blue light persists on faces, coming from phones forgotten under the pillow or too reassuring night lights. Banal gestures which nevertheless disrupt an age-old mechanism: the circadian rhythm. A monumental study has just confirmed its biological price. Published in JAMA Network Open, it reveals that exposure to artificial light at night increases the risk of heart failure by 56% and that of heart attack by 47%, compared to the darkest nights.

To obtain these results, Flinders University researchers analyzed a massive volume of data. Specifically, they studied more than 13 million hours of light exposure in 88,905 British adults. All were over 40 years old and wore a sensor on their wrist, day and night. By cross-referencing this data with the medical history and lifestyle of the participants, a correlation emerged. Night light has emerged as a cardiovascular risk factor in its own right.

When night light disrupts the body's signals

Human beings are not designed to sleep in full light. Its internal clock, regulated by the day-night alternation, controls vital functions such as blood pressure, heart rate and the release of hormones. In the absence of darkness, this biological conductor loses his bearings. The team led by Daniel Windred, also lead author of a second publication in PNAS, demonstrated that ambient light above 105 lux between midnight and 6 a.m. seriously disrupted these mechanisms.

This disruption leads to several chain reactions. The heart accelerates, tension rises and inflammation gradually sets in. In addition, the risk of arrhythmia increases significantly. In the long term, researchers sometimes see a progression towards heart failure or stroke. The phenomenon affects women and young adults more strongly. In them, sensitivity to light seems more marked. These effects remain visible even when taking into account lifestyle or genetics.

A world too lit to stay healthy

Night light now goes beyond the simple framework of modern comfort. It is gradually becoming a real public health issue. The Flinders University team, cited by New Atlas, calls for a review of domestic, urban and medical lighting. This change would be as fundamental as nutritional advice or physical activity. Moreover, the risks do not only concern the heart. Other studies carried out by these researchers show a clear link with type 2 diabetes. The people most exposed see their risk increase by 67%.

Conversely, exposure to broad daylight seems beneficial. Participants who benefited from bright natural lighting during the day saw their risk of cardiovascular mortality drop by up to 34%, according to the cross-analysis relayed by Flinders University. Daylight strengthens the internal clock signal, consolidates sleep-wake cycles and improves metabolic functions.

Faced with these findings, researchers are proposing simple and inexpensive solutions: turning off screens one hour before bedtime, using blackout curtains, favoring low-intensity lamps in the evening. Innocuous actions that could become the foundations of a new cardiac prevention strategy.