A new study from Tulane University has found that sleeping with a light on could raise the risk of serious cardiovascular problems, adding to a growing body of research on how nighttime light exposure affects long-term health.
Researchers determined that exposure to more than 3 lux of light while sleeping — about the brightness of moonlight — was associated with higher risks of heart failure, atrial fibrillation, heart attack, stroke and cardiovascular death.
Experts who spoke with Fox News Digital say the findings point back to the body’s circadian rhythm, the internal 24-hour clock that governs sleep and wakefulness.
How Light Disrupts Sleep
“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,” said Chelsie Rohrscheib, Ph.D., a Michigan-based sleep expert and neuroscientist.
“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,” she said.
Rohrscheib warned that consistent nighttime light exposure chronically reduces sleep quality, which in turn interferes with processes the body depends on.
“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,” Rohrscheib said. “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.”
Rohrscheib also pointed to a 2022 Northwestern Medicine study that found just one night of sleeping with moderate light exposure (100 lux) disrupted glucose regulation while increasing heart rate and sympathetic nervous system activity, reflected by reduced heart rate variability.
Ashley Curtis, Ph.D., a sleep researcher and assistant professor at the University of South Florida College of Nursing, said impaired sleep is also tied to a higher risk of mortality.
“Emerging evidence even suggests that it affects the gut microbiome, everything from digestion to immunity,” Curtis said. “While the immediate evidence is strongest for disrupted sleep health, the downstream risks to your long-term health are substantial.”
Some Groups More Vulnerable Than Others
Experts say certain populations may be more sensitive to nighttime light’s effects on sleep depth.
“Shift workers, children, older adults and individuals with insomnia or mood disorders are especially vulnerable to the effects of light on sleep depth,” said Alex Dimitriu, M.D., a double board-certified sleep medicine doctor and founder of Menlo Park Psychiatry & Sleep Medicine.
Curtis noted that older adults often become less sensitive to light overall, meaning bright or short-wavelength light has a weaker melatonin-suppressing effect 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 said.
There is also evidence that bright light has a more pronounced effect on melatonin suppression in men, according to Curtis. For people who already have insomnia, bright light before bed can make the underlying problem worse by further disrupting the circadian rhythm, she warned.
Not All Light Is Equal
Dimitriu said blue wavelength light — the kind emitted by TVs and phones — is the most disruptive to sleep because the retina is especially sensitive to it, causing maximal melatonin suppression.
“Dim, warm, red-toned night lights cause far less circadian impact – these are natural sunset colors one would see in the evenings,” he said.
Curtis agreed, noting that warmer, dimmer, longer-wavelength light has less 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.”
Still, Curtis said total darkness isn’t required for a healthy sleep environment. “While blackout curtains are recommended for optimal sleep, you don’t need to have absolute darkness to maintain a healthy sleep environment,” she said.
