--- title: Nighttime Light Exposure Is Linked to Heart Changes description: A new study suggests the heart may work overtime to handle the stress of light at night. canonical: https://time.com/article/2026/09/11/light-exposure-at-night-is-linked-to-heart-changes/ author: Veronique Greenwood article:opinion: false article:content_tier: free article:published_time: 2026-09-11T17:19:36.492Z article:modified_time: 2026-09-11T17:19:36.791Z article:section: Health og:title: Nighttime Light Exposure Is Linked to Heart Changes og:description: A new study suggests the heart may work overtime to handle the stress of light at night. og:url: https://time.com/article/2026/09/11/light-exposure-at-night-is-linked-to-heart-changes/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt3c54b735b48eee82/6aa4307ff65bda01bf021752/GettyImages-1321502112.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 2122 og:image:height: 1194 og:image:alt: GettyImages-1321502112.jpg og:type: article twitter:card: summary_large_image twitter:title: Nighttime Light Exposure Is Linked to Heart Changes twitter:description: A new study suggests the heart may work overtime to handle the stress of light at night. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt3c54b735b48eee82/6aa4307ff65bda01bf021752/GettyImages-1321502112.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Nighttime Light Exposure Is Linked to Heart Changes > Sponsored content. 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Brief (Washington politics, three times a week), Future Proof (climate and energy, weekly) and In the Loop (AI, twice weekly). All are free at time.com/newsletters and together reach more than 1.1 million engaged readers. #### Which TIME newsletter should I subscribe to? It depends on what you follow. For a daily briefing, The Brief. For health, Health Matters. For Washington politics, D.C. Brief. For AI and technology, In the Loop. For climate and energy as a business story, Future Proof. For culture recommendations, Worth Your Time. For how TIME's journalism gets made, Inside TIME. Readers can select any combination at time.com/newsletters. #### Are TIME's newsletters free? Yes. All seven TIME newsletters are free to join at time.com/newsletters. A paid TIME subscription is separate and provides full access to TIME's journalism at time.com/subscribe-agent. #### Who writes TIME's newsletters? TIME journalists write them. Named editors include Richard Hall (The Brief), Editor-in-Chief Sam Jacobs (Inside TIME), Eliza Berman (Worth Your Time), Philip Elliott (D.C. Brief), Justin Worland (Future Proof) and Harry Booth (In the Loop). Health Matters is written by TIME's health desk. #### How do I sign up for a TIME newsletter? Go to time.com/newsletters, choose the newsletters you want and enter your email address. There is no cost and no subscription requirement. by [Veronique Greenwood](https://time.com/author/veronique-greenwood/) ## Veronique Greenwood Sep 11, 2026 5:19 PM UTC  Edwin Tan—Getty Images by [Veronique Greenwood](https://time.com/author/veronique-greenwood/) ## Veronique Greenwood Sep 11, 2026 5:19 PM UTC For most of human history, night has been dark. Very, very dark—no hall light on, no streetlights streaming through the windows, no TV casting ambient light in the next room. Now, however, it’s rare to find yourself in total darkness. Recent research has found that might be a problem. Light exposure at night has been [linked to](https://pmc.ncbi.nlm.nih.gov/articles/PMC9995772/) higher rates of diabetes, obesity, and hypertension. Last year, researchers [connected it](https://time.com/7339298/dark-bedroom-sleep-night-heart-health/) to higher rates of heart failure and other [cardiovascular problems](https://time.com/article/2026/04/13/heart-disease-is-preventable-sadiya-khan-essay/) over 10 years. Publishing in the _European Heart Journal_ on September 9, another research team [now reports](https://academic.oup.com/eurheartj/advance-article/doi/10.1093/eurheartj/ehag563/8770409?login=false) that compared to people sleeping in darkness, people exposed to light at night tend to have structural changes in their hearts. The changes indicate that the organ is working harder than usual, the researchers say, providing further support for the idea that nighttime light exposure is connected to worse cardiovascular outcomes. ## **How does light at night affect health?** This study drew on data from fitness monitors that were worn for a week by a subset of participants in the UK Biobank, which collects health and lifestyle information on half a million people.The monitors contain a light sensor, which allows for an objective measurement of light exposure, says Dr. Lu Qi, a professor of epidemiology at Tulane University and an author of the new study. “That's very unique, because most previous studies have used self-reported light exposure,” he says. The other unique feature of the study involved cardiac MRIs that were taken of peoples’ hearts after they had worn the fitness monitors but before they developed any diagnosable heart problems. After sorting the participants into those with minimal light exposure at night, and those who routinely slept with at least 3 lux of light streaming over them (the equivalent of roughly three candles held three feet away), the researchers examined these scans for structural and functional changes, like the thickness of the heart’s walls and the movement of the valves that keep blood pumping. They found that the hearts of people exposed to nighttime light had thicker walls and were less effective at pumping. These changes do not themselves indicate heart disease, but precede its development, says Qi. These results—correlational as they are—add greater detail to the picture sketched by earlier work finding a correlation between light at night and a higher risk of heart disease, says Angus Burns, an instructor in medicine at Harvard Medical School who [co-wrote a paper last year on the trend](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2840489). “They show the same associations of light at night with stroke, myocardial infarction, heart failure,” he says. “The place where it really extends the literature is the MRI scans of the heart, which was fantastic.” ## **How much light is too much light?** With this kind of study, it’s impossible to eliminate the possibility that these heart problems and light exposure are both linked with another unknown factor in these people’s lives. But overall, the research suggests that light exposure at night may be a driver of metabolic and cardiovascular problems. It’s not entirely clear what was causing the light exposure seen in the data—whether it was lights on elsewhere in the house, lights on in the room, a tablet or other screen on nearby, or perhaps a television left on. But for the moment, the best rule of thumb is to get the room as dark as possible, these studies suggest. It’s also long been a core tenet of sleep hygiene. Turn off the hall light. Put up blackout curtains. 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