If You Do This While Sleeping, You Could Be Hurting Your Heart, New Study Says

Research shows your room should be free of one thing while you're snoozing.

It's no secret that getting enough sleep is vital for your health. But even though establishing a routine that will get you into bed early enough is important, the quality of your shuteye can be just as essential as how many hours you manage to get. In fact, new research says that you could be hurting your heart by not avoiding one thing while sleeping. Read on to see what shouldn't be part of your slumber.

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Sleeping with any lights on could increase your heart disease and diabetes risk.

woman sleeping with light on in bedroom

In a study published on March 14 in the journal Proceedings of the National Academy of Sciences, 20 participants aged 19 to 36 were invited to spend two nights sleeping in a lab. All participants were then provided with a dark room to sleep in during the first night. However, half of the participants spent the second night in a room illuminated by 100 lux—equivalent to the glow of a TV or a streetlight through a window—while the other half slept in complete darkness, Smithsonian Magazine reports.

Before going to bed, the researchers connected participants to IV tubes that allowed researchers to monitor their blood while they slept without waking them. The team also measured other sleep quality and health metrics, including their brain waves, hormone levels, and heart rates throughout the night. In the morning, the team took additional tests to measure glucose and insulin levels and administered a dose of glucose to participants to record their body's insulin response. Results found that not only did participants who slept in dimly lit rooms get less restorative sleep, but they also had 25 percent higher levels of insulin in their bloodstream in the morning as well as a higher average heart rate than those who slept in dark rooms.

"The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes, and metabolic syndrome," Phyllis Zee, MD, PhD, the study's senior author and chief of sleep medicine at Northwestern University Feinberg School of Medicine, said in a statement. "It's important for people to avoid or minimize the amount of light exposure during sleep."

Being exposed to even minimal light while sleeping can stop the body from resting properly.

Woman sleeping
Stock-Asso / Shutterstock

The study's findings helped support previous research, which has found that exposure to light during the day can increase your heart rate due to a response generated by your body's sympathetic nervous system. Typically, this allows you to become more alert during waking hours. But by being activated during sleeping hours, your body is missing out on crucial restoration time that the body needs to stave off serious health issues.

"We showed your heart rate increases when you sleep in a moderately lit room," Daniela Grimaldi, MD, PhD, a co-first author of the study and research assistant professor of neurology at Northwestern, said in a statement. "Even though you are asleep, your autonomic nervous system is activated. That's bad. Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day."

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Avoid exposure to light near bedtime and keep any illumination in your room to a bare minimum.

A young woman lying in bed while using her smartphone

Based on the findings, Zee suggests making some alterations to your sleep surroundings. "I think the strength of the evidence is that you should clearly pay attention to the light in your bedroom," she told CNN. "Make sure that you start dimming your lights at least an hour or two before you go to bed to prepare your environment for sleep."

Besides being sure to not use harsh LED lightbulbs where you sleep, you should also be aware of the devices creating brightness in your room, such as laptops, TV screens, phones, or tablets. "Blue light is the most stimulating type of light," Zee said. "If you have to have a light on for safety reasons, change the color. You want to choose lights that have more reddish or brownish tones."

If you can't change your sleep environment, Zee recommends installing blackout curtains in your room or using an eye mask to block out light. It can also help to rearrange your room so that any outside lighting doesn't shine on you while sleeping.

Other research has found that sleeping on your left side could harm your heart.

A senior sleeping while holding his heart in discomfort

But it's not just about finding the proper lighting when it comes to resting conditions and cardiovascular health: Other scientists have also explored how sleeping in different positions could potentially affect your heart, Healthline reports. One such study conducted in 1997 tested 40 subjects—18 of whom had been diagnosed with heart disease and 22 considered healthy—using an electrocardiogram (ECG) to monitor electrical activity in the heart while they switched between sleeping on their back and sides. Results showed that participants sleeping on their left side saw the most significant changes to their ECG ratings while resting.

A separate study conducted in 2018 also used ECG to monitor the heart data from 9 subjects. Similar to the 1997 study, results also found that participants sleeping on their left sides had significant changes in their heart's electrical activity. But in this study, an imaging technique known as vectorcardiography also showed that the heart turned and shifted while in that position, which researchers said may explain the recorded changes. In comparison, almost no ECG changes were recorded while participants slept on their right side, likely due to a thin layer of tissue between the lungs known as the mediastinum actually holding the heart securely in place while sleeping that way, Healthline says.

However, both studies quickly concluded that more research would be needed on how sleep position could affect the heart's activity overall. And while some patients who have been diagnosed with congestive heart failure have reported trouble breathing or discomfort while sleeping on their left side, there is no conclusive evidence that sleeping on your left side could be putting you at an increased risk of heart disease if you don't already have a condition.

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Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
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