Sleeping with lights on, even at low levels, has been associated with an increased risk of cardiovascular disease, according to a new study from Tulane University. Researchers found that exposure to more than 3 lux of light, comparable to moonlight, was linked to higher risks of heart failure, atrial fibrillation, heart attack, stroke, and cardiovascular death.
Sleep plays a critical role in numerous bodily functions, including the restoration of the body and brain, hormone regulation, immune system performance, memory consolidation, waste clearance from the brain, and metabolic regulation. The body's internal 24-hour clock, known as the circadian rhythm, which governs sleep and wakefulness, is heavily influenced by light. Light exposure signals the brain to suppress melatonin production, a hormone essential for regulating sleep timing. Conversely, low light levels prompt the brain to increase melatonin.
"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," explained Chelsie Rohrscheib, Ph.D., a sleep expert and neuroscientist.
A 2022 study by Northwestern Medicine highlighted that even a single night of moderate light exposure (100 lux) disrupted glucose regulation and increased heart rate while reducing heart rate variability, indicating heightened sympathetic nervous system activity. Ashley Curtis, PhD, a sleep researcher and assistant professor at the University of South Florida College of Nursing, noted that sleep impairment is also connected to an increased risk of mortality and may affect the gut microbiome, impacting digestion and immunity.
Certain individuals may be more susceptible to the effects of nighttime light. These include shift workers, children, older adults, and those with insomnia or mood disorders. While older adults may become less sensitive to light, they often experience a higher prevalence of sleep disruption, which can negatively impact their circadian systems.
Blue wavelength light, commonly emitted by screens such as TVs and phones, is considered particularly disruptive due to the eye's sensitivity to it, leading to maximum suppression of melatonin. In contrast, dim, warm, red-toned night lights produce less circadian impact, as these colors mimic natural sunset hues. Warmer, dimmer light with longer wavelengths has a less pronounced effect on melatonin production, allowing the body more time to recover.
To cultivate a healthier sleep environment, experts recommend several practical changes. These include turning off bright overhead lights one to two hours before bed, placing night lights close to the floor, and using dimmer bulbs that emit warmer colors like orange, amber, or red. It is also advised to cease all screen use at least one hour before bedtime to avoid stimulating the brain. Layering window treatments can help soften external bright lights, and using a sleep mask can further prevent light pollution from impacting sleep quality.