A new study from Tulane University is raising fresh concerns about sleeping with a light on, linking nighttime light exposure to a higher risk of cardiovascular disease.
Researchers found that exposure to more than 3 lux of light — roughly the brightness of moonlight — was associated with increased risks of heart failure, atrial fibrillation (irregular and often very rapid heart rhythm), heart attack, stroke and cardiovascular death.
Experts spoke with Fox News Digital about the potential risks associated with sleeping with a nightlight.
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Sleep is partially controlled by the circadian rhythm, the brain’s internal 24-hour clock that regulates sleep and wakefulness, according to sleep expert and neuroscientist Chelsie Rohrscheib, Ph.D., a sleep expert and neuroscientist based in Michigan.
“The circadian rhythm is strongly influenced by light entering the eyes – light exposure signals the brain to suppress melatonin production, a hormone that helps regulate the timing of sleep, while low light levels signal the brain to produce more melatonin,” she told Fox News Digital.
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“As melatonin levels rise in the evening, they help prepare the brain and body for sleep. Light pollution from various sources in our bedroom can trick the brain into producing less melatonin, which can negatively impact sleep quality.”
Consistent light exposure will chronically reduce overall sleep quality, Rohrscheib warned.
“Sleep plays an essential role in many biological processes, including body and brain restoration, hormone release, immune system functioning, cognitive processes such as memory consolidation, brain waste clearance and metabolic regulation,” she said.
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“When sleep is consistently poor, these processes do not function optimally, which in turn elevates the risk for many chronic health conditions such as hypertension, cardiovascular disease, stroke, type 2 diabetes, obesity, neurodegenerative diseases, certain cancers and mood disorders.”
A 2022 Northwestern Medicine study found that just one night of sleeping with moderate light exposure (100 lux) disrupted glucose regulation while increasing heart rate and sympathetic nervous system activity, as reflected by reduced heart rate variability (HRV), Rohrscheib noted.
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Sleep impairment is also linked to increased risk of mortality, according to Ashley Curtis, PhD, sleep researcher and assistant professor at the University of South Florida College of Nursing.
“Emerging evidence even suggests that it affects the gut microbiome, everything from digestion to immunity,” she told Fox News Digital. “While the immediate evidence is strongest for disrupted sleep health, the downstream risks to your long-term health are substantial.”
Certain groups may be more sensitive to nighttime light than others, experts agree.
“Shift workers, children, older adults and individuals with insomnia or mood disorders are especially vulnerable to the effects of light on sleep depth,” Alex Dimitriu, M.D., a double board-certified sleep medicine doctor and founder of Menlo Park Psychiatry & Sleep Medicine, told Fox News Digital.
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Curtis noted that older adults often become less sensitive to light, meaning bright or short-wavelength light has a weaker effect on suppressing melatonin than it does in younger adults.
“The caveat, however, is that older adults also experience a higher baseline prevalence of sleep disruption, which can bidirectionally impact the circadian system,” she added.
There is also some evidence showing that bright light has a more pronounced impact on melatonin suppression in men, the expert noted.
For people with insomnia, who already experience chronic sleep disruption, bright light exposure before bedtime can make these underlying problems worse, as it further interferes with the biological circadian rhythm, Curtis warned.
Blue wavelength light from TVs and phones is the most disruptive because people’s retinas are most sensitive to it, and it maximally suppresses melatonin, according to Dimitriu.
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“Dim, warm, red-toned night lights cause far less circadian impact – these are natural sunset colors one would see in the evenings,” he told Fox News Digital.
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Curtis agreed that warmer, dimmer light, which has a longer wavelength, doesn’t have as much impact on melatonin production.
“Research shows that even if dim light impacts melatonin initially, it allows time for the body to recover,” she said. “Therefore, it doesn’t disrupt your sleep to the degree that brighter light does.”
“While blackout curtains are recommended for optimal sleep, you don’t need to have absolute darkness to maintain a healthy sleep environment,” Curtis said.
The experts recommend implementing the following changes to cultivate a healthy sleep environment – even if it’s not pitch black.
