Study links sleeping with night-time light to higher risk of heart disease and stroke
Researchers at Tulane University found that exposure to low-level light while sleeping is associated with increased incidence of heart failure, atrial fibrillation, heart attack, stroke and cardiovascular mortality.
A Tulane University study reported that sleeping with a light source emitting more than 3 lux – roughly the brightness of moonlight – correlates with higher rates of heart failure, atrial fibrillation, myocardial infarction, stroke and death from cardiovascular causes. The researchers analyzed health records and found the risk rose with nighttime light exposure above this threshold.
Sleep scientist Chelsie Rohrscheib, Ph.D., explained that light entering the eyes suppresses melatonin, the hormone that signals the body to prepare for sleep. "The circadian rhythm is strongly influenced by light entering the eyes – light exposure signals the brain to suppress melatonin production, while low light levels signal the brain to produce more melatonin," she said.
Rohrscheib warned that chronic reduction in melatonin can diminish sleep quality, which in turn impairs processes such as hormone release, immune function and metabolic regulation, increasing the likelihood of hypertension, cardiovascular disease, stroke, diabetes and other chronic conditions.
Sleep researcher Ashley Curtis, Ph.D., noted that poor sleep also affects the gut microbiome and overall mortality risk. She added that older adults may experience weaker melatonin suppression from bright light but still face higher baseline rates of sleep disruption.
Sleep physician Alex Dimitriu, M.D., said shift workers, children, older adults and people with insomnia or mood disorders are especially vulnerable to nighttime light. He identified blue-wavelength light from screens as the most disruptive, while dim, warm, red-toned nightlights have a far lesser effect on melatonin.
The experts suggested practical steps such as using blackout curtains or low-intensity, warm-colored nightlights to minimize circadian disruption without requiring complete darkness.