Nighttime light exposure linked to cardiac remodeling and higher cardiovascular risk

A new study suggests that light exposure during sleep could raise the risk of cardiovascular disease. Yana Iskayeva/Moment/Getty Images New research shows that even dim light during sleep may thicken heart muscle walls and reduce heart flexibility, potentially raising cardiovascular risk.  The findings build on prior evidence linking nighttime light exposure to cardiovascular disease risk. Optimizing your sleep environment can help protect your heart health. Sleeping in dark conditions may be important not only for quality sleep but also for heart health. New research suggests that nighttime light exposure is associated with subtle changes in the heart, and even low levels of light — as low as 3 lux — could have negative effects over time. For context, moonlight is less than 3 lux, whereas the glow of a smartphone is much higher. Researchers analyzed data from more than 11,000 UK Biobank participants who wore wrist devices measuring light exposure. At around a three-year follow-up, the researchers used cardiovascular magnetic resonance imaging (MRI) to examine their hearts. Participants exposed to higher levels of nighttime light showed signs of cardiac remodeling, including slightly thicker heart muscle and subtle changes in heart contraction. These changes, the researchers noted, could lead to heart failure or atrial fibrillation (AFib). Prior observational studies have linked nighttime light exposure to a higher risk of cardiovascular disease, but the effects on the heart’s structure and function were less understood.  The new study builds on evidence connecting nighttime light exposure and cardiovascular disease, but cannot prove that light itself causes these changes. The findings were published in the European Heart Journal on September 9. “This is the first study of its kind, and it shows that exposure to higher levels of light at nighttime is linked to cardiac remodeling,” lead study author Lu Qi, MD, PhD, a professor in the Epidemiology Department at Tulane University and director of the Tulane University Obesity Research Center, said in a news release. “This is where the structure and function of the heart changes and we typically see it in response to chronic stress or injury to the heart. It’s our body’s way of adapting to that stress, but ultimately it weakens the heart and can lead to heart failure,” Qi continued. Low-level light exposure during sleep linked to heart changes Researchers focused on nighttime light exposure above 3 lux, a relatively low level of illumination. This threshold was used to distinguish participants who experienced measurable nighttime exposure from those who did not. Compared with participants with no nighttime exposure above 3 lux, those with higher exposure had a 2.4% greater left ventricular mass, a 1.5% greater average heart wall thickness, and a 1.9% lower myocardial contraction fraction.  The researchers also observed impaired myocardial deformation and subtle changes involving the right ventricle and left atrium. These differences were small and did not indicate cardiovascular disease.  However, they may offer clues about how nighttime light exposure could contribute to cardiovascular problems over the long term. According to Qi, these heart changes could lead to the development of atrial fibrillation (AFib) or heart failure. “Our data indicate short sleeping may account for a high proportion of the observed adverse association, suggesting nighttime exposure may affect sleep duration and quality, which subsequently increases CVD risk,” Qi told Healthline. Cheng-Han Chen, MD, a board certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, said that while the exact mechanisms of this association are not fully understood, several factors may be involved. Chen wasn’t part of the study. “Previous research has linked nighttime light exposure with cardiovascular risk factors such as high blood pressure, high cholesterol, obesity, and diabetes,” Chen told Healthline.  “Over time, these conditions can contribute to changes in the heart’s structure and function and increase cardiovascular risk. Nighttime light may also disrupt the body’s natural circadian rhythm, which plays an important role in regulating blood pressure, metabolism, sleep, and healthy heart function.” Nighttime light exposure and cardiovascular disease risk The MRI findings in the present study are consistent with a 2025 JAMA Network Open study involving nearly 89,000 UK Biobank participants.  Researchers measured personal light exposure for one week and followed cardiovascular outcomes for about 9.5 years. Compared with people exposed to the darkest nighttime conditions, those in the brightest-light group had higher risks of coronary artery disease, heart attack, heart failure, AFib, and stroke.  The risks were 32% higher for coronary artery disease, 47% higher for heart attack, 56% higher for heart failure, 32% higher for AFib, and 28% higher for stroke. The researchers observed a dose-response pattern, with cardiovascular risk generally increasing as nighttime light exposure increased.  Still, these were observational findings and cannot establish that light directly caused cardiovascular disease.  However, a 2024 review of more than 1 million participants from 14 studies similarly found that greater exposure to light at night was associated with a higher risk of cardiometabolic disease. Circadian rhythm disruption may play a role The circadian rhythm is the body’s internal 24-hour clock that regulates sleep, hormones, and cardiovascular processes. Light is one of the body’s strongest signals for setting its internal clock. Disruptions from nighttime light exposure could impair circadian signaling and suppress melatonin, potentially interfering with sleep quality.  In the new study, shorter sleep was responsible for 24–49% of the associations between nighttime light exposure and several cardiac measurements. Nighttime light can come from televisions, phones, and nightlights, as well as streetlights and illuminated buildings outside the home.  Research has shown an association between indoor and outdoor nighttime light and cardiovascular outcomes. “Higher levels of nighttime light exposure have been associated with an increased risk of several cardiovascular conditions, including heart failure, atrial fibrillation, heart attack, and stroke,” Chen said.  “Some research has also found an association with a higher risk of cardiovascular death. However, these associations do not necessarily mean that nighttime light directly causes these conditions. More research is needed to better understand the relationship.” Optimizing your bedroom for quality sleep More research is needed to determine whether reducing nighttime light directly improves heart health and whether the cardiac changes observed are reversible. Still, there are many benefits to sleeping in a dark bedroom. “Good sleep habits are also important. When possible, keep the bedroom as dark as reasonably possible at night and maintain a consistent sleep schedule,” Chen said. While eliminating all light, even the smallest glow, might not be possible, there are simple strategies to avoid circadian disruption and support quality sleep. Use blackout curtains or shades if outdoor light enters your bedroom. Turn electronics away from the bed and cover unnecessary indicator lights. Keep your phone face down or outside the bedroom when practical. If you need a nightlight, use the dimmest warm-colored light that provides adequate visibility. Maintain relatively consistent sleep and wake times. Get bright natural light during the daytime, especially in the morning, to reinforce your circadian rhythm. Those who live in brightly lit urban environments or experience disrupted sleep may need to take extra measures to optimize their sleep environment.  “If avoiding nighttime light is difficult, focus on the cardiovascular risk factors you can control,” Chen said. “This includes eating a heart-healthy diet low in saturated fat and sodium, getting regular physical activity, maintaining a healthy weight, and avoiding tobacco and excessive alcohol.”

Many people sleep with a night-light their whole lives—though as they grow older, small plug-in light fixtures may be replaced by the glow of laptops or phone screens. While sleeping in a low level of light may be commonplace, doing so comes with its own health hazards, including altering the shape of the human heart.A new study, published this week in the European Heart Journal, links exposure to light while sleeping to cardiac remodeling, or changes to the shape and function of the heart. Specifically, light exposure during sleep led to thickening of the wall of the left ventricle, one of the organ’s four chambers, reducing the space inside the heart. That weakens its ability to flex during a heartbeat, setting the stage for cardiac dysfunction. “Light pollution has emerged as a new risk factor for cardiovascular disease,” Dr. Lu Qi, a professor at Tulane University and an author of the study, said in a press release. “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 policymakers.” How much light is too much light? To determine how light exposure during sleep impacts cardiovascular health, the study’s researchers analyzed the sleep habits of 11,071 participants. Subjects wore a light sensor on their wrists while sleeping for seven days. Three years later, their hearts were scanned via cardiac MRIs to assess their structure and function. Those who were exposed to more than 3 lux overnight saw significantly more cardiac remodeling compared with those who slept in near complete darkness. Lux, the International System unit for light exposure, measures how much light falls on a given surface area.Three lux, the study’s benchmark for a high level of light exposure, may not seem like much light at all. It’s equivalent to the brightness of deep twilight, or to the amount of light that bleeds under a door from a bright adjacent room. A phone screen, meanwhile, can top out around 80 lux, according to experts. With 58% of U.S. adults saying they use their phone within an hour of bedtime or while in bed as they fall asleep, that’s more than half of Americans who may be unknowingly setting themselves up for heart problems in the future. How to sleep more safely To avoid light exposure during sleep, experts recommend using blackout curtains or sleep masks and covering small standby lights on electronics. Limiting screen time immediately before bed (and especially while falling asleep) is important, too. For the best quality sleep, ambient light should be limited to a maximum of just 1 lux, which is close to total darkness. In an article accompanying the study, cardiologist Thomas Münzel and his colleagues spoke to how its results might inform the future of medicine, including the questions doctors ask their patients during health screenings. “It is time for clinicians, particularly those managing patients with heart failure or atrial fibrillation, to start asking about the sleep environment: how dark the bedroom is, whether the patient works night shifts, and how much screen use occurs after sunset,” Münzel wrote. “Darkness deserves recognition as a vital sign, as essential to cardiovascular health as blood pressure control and clean air.”