Could Your Nighttime Light Be Hurting Your Heart?

Here’s something to think about next time you’re scrolling your phone in bed or leaving the hallway light on: a major study suggests that exposure to light at night might be raising your risk of heart disease.

Researchers tracked nearly 89,000 adults in the UK for almost a decade. Instead of relying on estimates or questionnaires, they had participants wear wrist-mounted light sensors for a week to measure their actual light exposure. Then they followed up through medical records to see who developed cardiovascular problems.

The results were striking. People with the highest nighttime light exposure had a 42% higher risk of heart attack, 45% higher risk of heart failure, and roughly 28% higher risk of stroke and atrial fibrillation compared to those who kept things dark at night. And this wasn’t explained away by other factors—the researchers accounted for age, weight, diet, exercise, smoking, sleep quality, shift work, and even genetic predisposition to heart disease. The association still held.

So what’s going on? Light is the main signal that sets your body’s internal clock. When light hits your eyes at night, it can throw off the normal rhythms that regulate everything from blood pressure to metabolism. Your blood pressure is supposed to dip while you sleep, but nighttime light can prevent that drop. It can also push your nervous system into a more stressed state and mess with how your body handles glucose and fats. Over time, these disruptions may take a toll on your cardiovascular system.

What makes this study particularly relevant is that the light levels involved weren’t unusual. We’re not talking about working night shifts under fluorescent lights. The exposures that showed up as risky came from everyday sources—phone screens, bedside lamps, streetlight creeping through the curtains. Things most of us encounter regularly.

The study isn’t perfect. Measuring light for just one week might not capture someone’s typical long-term habits, and observational research can’t prove cause and effect with certainty. But the findings are consistent with what we know about circadian biology, and the dose-response pattern (more light, more risk) adds credibility.

The practical takeaway? Dimming the lights in the evening, using blackout curtains, and putting away screens before bed aren’t just good sleep hygiene—they might be good for your heart too.

Photo by Jakub Żerdzicki on Unsplash