Sleeping With the Lights On May Affect Your Heart, Study Finds

• Researchers detected subtle changes in heart structure
• Greater light exposure was associated with cardiovascular risk
• Sleeping in darkness may support healthier rest

Sleeping with the TV on, a phone screen illuminating the room, or even small lights from electronic devices could have consequences beyond disrupting rest.

A new study published in the European Heart Journal found an association between light exposure during sleep and subtle changes in the structure and function of the heart.

The research, reviewed by NBC News, USA Today, and Healthline, is notable because the changes appeared even with relatively low levels of nighttime illumination.

Scientists examined exposure beginning at 3 lux, a level that still represents a very dim environment but can be detected through closed eyelids.

Why Can Nighttime Light Affect Sleep?

What Did Researchers Find in the Heart?

Researchers analyzed data from 11,071 UK Biobank participants who did not initially have cardiovascular disease.

For seven days, participants wore wrist sensors that recorded light exposure and movement. Years later, their hearts were evaluated using magnetic resonance imaging.

When researchers compared participants who slept in near-total darkness with those exposed to more nighttime light, they detected small but measurable differences.

On average, participants in the highest-exposure group had:

• 2.4% greater left ventricular mass in one of the heart’s main chambers.
• 1.5% greater heart-wall thickness.
• 1.9% lower myocardial contraction fraction, a measurement related to the heart’s ability to contract.

These differences do not mean that the participants had heart disease, but they are associated with a process known as cardiac remodeling—changes in the heart’s structure and function.

Lu Qi, the study’s lead researcher and a professor at Tulane University, explained that this type of remodeling can occur in response to chronic stress or injury and could weaken the heart over time.

Does Sleeping With the Lights On Increase the Risk of Heart Attack or Stroke?

During a follow-up period of up to 10 years, participants with greater nighttime light exposure had a higher associated cardiovascular risk than those with the lowest exposure.

Researchers reported associations with:

• A 29% higher risk of heart failure.
• A 24% higher risk of heart attack.
• A 33% higher risk of stroke.
• A 26% higher risk of cardiovascular death.

However, there is a crucial qualification: The study was observational.

That means its findings demonstrate an association but do not prove that sleeping with the lights on directly causes cardiovascular problems.

Participants also wore the sensors for only one week, and the study could not fully distinguish the effects of different types or wavelengths of light.

Why Might Light During Sleep Matter?

One possible explanation involves the circadian rhythm, the internal clock that organizes the body’s processes over an approximately 24-hour cycle.

This system helps regulate sleep, hormones, blood pressure, metabolism, and other processes connected to cardiovascular health.

Nighttime light exposure can disrupt these natural signals and affect both the duration and quality of sleep.

In fact, the study found that shorter sleep duration could explain a significant portion of the association between nighttime illumination and some of the observed heart changes.

Nighttime light can come from phones, televisions, nightlights, clocks, LED indicators, humidifiers, or outdoor lighting entering through windows.

What Can You Do to Reduce Light While Sleeping?

Experts emphasize that further research is needed to determine whether reducing nighttime light can reverse or directly prevent the observed heart changes.

However, maintaining a sufficiently dark bedroom is also part of standard recommendations for promoting healthy sleep.

Measures recommended by experts and sleep organizations include:

• Using blackout curtains or blinds when significant outdoor light enters the room.
• Covering unnecessary LED lights on televisions and other devices.
• Keeping the phone face down or outside the bedroom when possible.
• Using dim, warm-toned lighting when it is necessary to get up during the night.
• Reducing household lighting as bedtime approaches.
• Maintaining relatively consistent bedtime and wake-up schedules.
• Seeking exposure to natural light during the day, particularly in the morning.

Environmental cardiologist Thomas Münzel and other experts proposed a notable idea in an editorial published alongside the study: Nighttime darkness should be considered an important component of cardiovascular health, along with other environmental factors.

The study does not mean that a small bedroom light will cause heart disease. However, it adds to evidence suggesting that the environment in which people sleep could matter for heart health more than previously understood.

Warning: This information is intended for educational and informational purposes only and does not replace evaluation, diagnosis, or treatment by a healthcare professional. Consult a doctor if you experience symptoms or sleep problems or have a history of cardiovascular disease.

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SOURCES: NBC News / USA Today / Healthline / European Heart Journal, UK Biobank / National Sleep Foundation.