Light is supposed to signal your body that it’s time to rest, yet most people now sleep surrounded by it — streetlights streaming through the window, the glow of electronics, the standby light on the TV. What seems harmless is, in fact, an invisible stressor on your heart. Mounting evidence shows that artificial light at night interferes with your body’s ability to repair and regulate itself, setting the stage for the very diseases most people try to avoid through diet and exercise.
Heart disease — narrowed or hardened arteries that restrict blood flow — is influenced by poor lifestyle habits. But research suggests your nighttime environment plays a powerful role, too. When your internal clock is thrown off by light exposure, it triggers a cascade of changes: blood pressure creeps up, heart rate climbs, and inflammation rises. Over time, these small disruptions become the foundation for serious cardiovascular problems.
True recovery happens only in darkness. That’s when your body restores rhythm, balances hormones, and gives your heart a chance to rest. Yet for many people, that natural cycle is elusive. The simple act of dimming the light after sunset could make the difference between heart health and heart strain — and recent studies are revealing just how strong that connection really is.
Light Exposure at Night Linked to Cardiovascular Disease
A study published in JAMA Network Open analyzed about 13 million hours of light data from 88,905 adults aged 40 and older to determine whether brighter light at night increased cardiovascular disease risk.1
Over a 9.5-year follow-up period, researchers found that participants exposed to the brightest nighttime environments were significantly more likely to develop coronary artery disease, heart attack, heart failure, atrial fibrillation, and stroke. Those with the brightest nights — defined as the top 10% of nighttime light exposure — had up to a 56% higher risk of heart failure and 47% higher risk of heart attack compared to those with the darkest nights.
• The participants represented real-world living conditions across the U.K. — This research tracked individuals in their natural environments using wrist-worn light sensors instead of relying on satellite imagery. By following real people over time rather than relying on lab-based light exposure or self-reports, the study provided some of the most compelling evidence yet that the artificial glow surrounding us at night is harming our hearts.
• The more light participants were exposed to at night, the higher their risk of heart disease became — Those in the middle exposure range had slightly elevated risks, while those in the top range faced dramatically higher odds. For example:
◦ 32% higher risk of coronary artery disease
◦ 32% higher risk of atrial fibrillation (an irregular heartbeat)
◦ 28% higher risk of stroke
• Women and younger adults were the most affected — The study found that women and younger adults faced stronger effects from nighttime light exposure. The biological reason may lie in sex-specific circadian sensitivity — women’s internal clocks are more reactive to light signals, meaning that a small disruption causes larger hormonal and cardiovascular effects.
Similarly, younger adults have greater circadian responsiveness, which fades with age, making them more vulnerable to nighttime light’s biological disruptions.
• Light exposure at night confuses your body’s master clock — This is located in a brain region called the suprachiasmatic nucleus, which normally signals the release of melatonin, a hormone that promotes sleep and helps regulate blood pressure, blood sugar, and heart rate. When this rhythm is disturbed:
◦ Heart rate increases when it should be at rest.
◦ Blood pressure rises and stays elevated through the night.
◦ Inflammatory pathways activate, damaging blood vessels over time.
◦ The heart muscle becomes less efficient, leading to structural changes such as thickening of the walls and reduced pumping strength.
• Daytime light exposure had the opposite effect, offering protection — Participants exposed to brighter light during the day showed lower risks of coronary artery disease, heart failure, and stroke.
This highlights the importance of maintaining strong light-dark contrast: getting enough bright light in the morning and daytime while keeping nights as dark as possible. Your body’s internal rhythm depends on this contrast to maintain healthy cardiovascular and metabolic function.
Night Light and Dirty Air Team Up to Hurt Your Heart
For a study published in the Journal of the American Heart Association, researchers tracked 416,032 adults for almost 15 years and looked at air pollution and nighttime light around their homes to see who developed heart and blood vessel problems like heart attacks, heart failure, irregular heartbeat, stroke, or died from heart disease.2
• Worse air meant more heart problems — People living with the heaviest mix of pollution had higher chances of heart attack, heart failure, irregular heartbeat, and dying from heart disease than those in cleaner areas. Risk climbed step by step as fine particles and traffic fumes went up.
• Tiny particles and traffic gases were the biggest issue — The highest levels of fine particle pollution (PM2.5) and traffic gases were linked to about one-third higher risk of heart failure and roughly one-third higher risk of death from heart disease. Bigger, coarse dust mattered less.
• Bright nights added extra risk on their own — and on top of pollution — Living in brighter-at-night areas was tied to higher risks of heart attack, heart failure, irregular heartbeat, and death from heart disease. When people had both high pollution and high night light, their risk rose even more.
The brightness at night accounted for about 25% of air pollution’s added risk for heart attacks and about 20% to 39% of the extra risk for heart failure, depending on how polluted the area was.
• City brightness and pollution went hand in hand — Brighter-at-night neighborhoods also had higher fine particles and traffic fumes. As fine particles rose, night brightness typically rose, too, showing the two exposures often come as a package in cities.
Light at Night Disrupts Your Mind and Body Too
It’s not only your heart that suffers from exposure to light at night. Researchers from the Turner Institute for Brain and Mental Health in Melbourne, Australia, analyzed data from 86,772 adults to explore how day and night light exposure affects mood and mental health. They found that people who were exposed to more light at night had higher rates of depression, anxiety, post-traumatic stress disorder (PTSD), bipolar disorder, psychosis, and self-harm.3
• Too much light at night and too little in the day worsens mood balance — People who spent most of their day indoors but stayed under bright light in the evening had a 30% higher risk of depression. In contrast, those who received bright daylight exposure had a 20% lower risk of depression and better protection against PTSD and psychosis. This imbalance — dim days and bright nights — confuses your brain’s internal clock, making it harder to regulate mood and emotion.
• Circadian rhythm disruption alters how your brain and hormones work — Your circadian rhythm — the 24-hour biological cycle that coordinates sleep, hormone release, and metabolism — depends on bright light by day and darkness by night. Exposure to light at the wrong times shifts this rhythm, throwing off your sleep, hormone balance, and emotional regulation. Over time, this affects areas of your brain that control mood.
• Even dim light is enough to disturb your brain — Research shows that exposure to just five lux of light at night — about the brightness of a dim streetlamp — is linked with symptoms of depression.4 For perspective, the glow from a tablet produces about 40 lux. This suggests that even small amounts of artificial light during sleep send confusing “wake up” signals to your brain, interrupting deep rest and emotional recovery.
• Light at night is tied to physical health problems, too — The same body-wide stress response that disrupts mood also harms physical health. Studies show that nighttime light exposure increases your risk of obesity, diabetes, and high blood pressure. In one study, 40.7% of those exposed to light at night were obese — compared to just 26.7% among those sleeping in darkness.5
• Artificial light at night has even been linked to cancer risk — The World Health Organization classifies shift work involving light-at-night exposure as a probable human carcinogen because it disrupts circadian rhythms. Higher night light exposure has been tied to postmenopausal breast and thyroid cancers.6,7 One study following 464,371 adults found that those exposed to the brightest nighttime light had a 55% higher risk of thyroid cancer than those in the darkest areas.8
How to Protect Your Heart by Taking Back the Night
If you’ve ever struggled to sleep because your room isn’t truly dark, you’re not imagining the effects on your body. The same artificial light that helps you stay productive after sunset is quietly confusing your internal clock and keeping your heart from repairing itself overnight. What’s more, that same light affects far more than your heart — it influences your mood, hormones, metabolism, and even cancer risk.
Fortunately, the solution isn’t complicated. By making a few intentional changes to restore your natural light-dark cycle, you support not only your cardiovascular health but also your mental and metabolic well-being. These simple steps help you reclaim control of your environment, your recovery, and your long-term health.
1. Darken your nights completely — Your body needs real darkness to trigger melatonin and shift into repair mode. Even small light leaks — like the glow from a TV, phone, or streetlight — send “daytime” signals to your brain. Cover windows with blackout curtains or wear a soft, contoured sleep mask to block light. Avoid using electronics before bed, and dim every screen and switch bulbs to warm, low-intensity lighting at sunset. Think of this as giving your body permission to rest.
2. Strengthen your days with bright, natural light — Getting bright light early in the morning helps anchor your body clock and sets the stage for deeper, more restorative sleep at night. Open your blinds immediately after waking and step outside for 10 to 15 minutes of sunlight first thing in the morning.
If you work indoors, position your desk near a window or use a full-spectrum light box. Your goal is to reinforce a strong contrast — bright days and dark nights — which keeps your heart, hormones, and metabolism synchronized.
3. Build a calming nighttime routine that tells your body it’s safe to rest — If you go from full activity to bed with no transition, your nervous system stays on high alert. Choose a short ritual that helps you wind down — a warm bath, gentle stretching, or journaling under dim light.
Avoid scrolling on your phone or watching stimulating shows right before bed, since both the light and the emotional intensity keep your brain active. By repeating the same routine nightly, you train your body to expect rest, which steadies your heart rate and blood pressure through the night.
4. Keep technology from running your sleep environment — Many people unknowingly keep their rooms filled with electromagnetic fields (EMFs) and low-level light from chargers, alarm clocks, or standby LEDs. Cover or unplug anything that glows, and remove your cellphone from the bedroom. If you use a security device, disable any light indicators during sleep hours. Your bedroom should look like a dark cave — quiet, cool, and free from glowing distractions that interfere with your heart’s recovery rhythm.
5. Use darkness as a daily health habit, not a luxury — Protecting your heart isn’t only about food and exercise — it’s about giving your body the dark, quiet nights it evolved to depend on. Treat your sleep environment with the same seriousness as your diet or workout plan.
If you track your habits, note how much earlier you fall asleep and how refreshed you feel after eliminating light leaks. Seeing measurable progress reinforces your motivation and turns this into a lasting routine. The reward is steady energy, balanced hormones, and a heart that performs at its best every day.
FAQs About Exposure to Bright Light at Night
Q: How does light exposure at night increase heart disease risk?
A: Artificial light at night confuses your body’s internal clock, known as the circadian rhythm, which regulates heart rate, blood pressure, and inflammation. When this rhythm is disrupted, your heart can’t fully rest or repair itself. Over time, these nightly disturbances contribute to arterial damage, high blood pressure, and higher risks of heart attack, heart failure, and stroke.
Q: What did researchers discover about nighttime light and heart health?
A: In one large study published in JAMA Network Open, adults exposed to the brightest nighttime environments were up to 56% more likely to develop heart failure and 47% more likely to have a heart attack.9 Those who had the darkest nights showed the lowest rates of cardiovascular disease, while bright daylight exposure during the day offered protective benefits.
Q: Does light at night affect other parts of my body?
A: Yes. The same exposure that stresses your heart also harms your brain, mood, and metabolism. Research found that people exposed to more light at night had higher rates of depression, anxiety, PTSD, bipolar disorder, and self-harm. Nighttime light exposure has also been linked to obesity, diabetes, and certain cancers, including breast and thyroid cancers.
Q: How do air pollution and night light interact to raise cardiovascular risk?
A: A study in the Journal of the American Heart Association found that light pollution and air pollution often occur together, especially in urban areas.10 People exposed to both had the highest risks of heart attack, heart failure, and cardiovascular death. Nighttime brightness explained up to 39% of the extra heart failure risk linked to air pollution, showing that light exposure amplifies environmental damage to the heart.
Q: What can I do to protect my heart and mind from light pollution?
A: Make darkness part of your health routine. Keep your bedroom completely dark with blackout curtains or a sleep mask, remove glowing electronics, and use dim, warm lights in the evening. In the morning, expose yourself to bright natural light within 30 minutes of waking to reset your body clock. This simple daily rhythm — bright days, dark nights — helps your heart, hormones, and mood stay in sync.
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