Light pollution during nighttime sleep — even exposure as weak as moonlight or a beam of light coming through a gap under a door — can negatively affect the human heart, according to a new study published in the European Heart Journal.
“Exposure to higher levels of light at night is associated with cardiac remodeling,” said Lu Qi of Tulane University in New Orleans, USA, who led the study, in a press release. “This refers to changes in the structure and function of the heart that we typically observe in response to chronic stress or damage to the heart muscle.”
According to Qi, although the body adapts to stress in this way, “ultimately, it weakens the heart and may lead to heart failure,” Euronews reports.
Therefore, Qi said, keeping the bedroom as dark as possible “should be considered by clinicians and policymakers as one possible strategy for preventing heart disease.”
The study included 11,071 people who were exposed to different levels of light at night for one week, ranging from almost complete darkness to varying degrees of illumination — up to light comparable to the glow of a phone screen at low brightness or a beam of light coming through a partially open door.
Three years later, the participants underwent cardiovascular magnetic resonance imaging (MRI) to identify possible changes in the structure and function of the heart.
The results showed that participants exposed to the highest levels of nighttime light developed thickening of the walls of the heart's left ventricle, reducing the space inside the chamber. There were also signs of a reduced ability of the heart to contract with each beat, an early indicator of impaired cardiac function.
“Darkness deserves recognition as a vital sign, as essential for cardiovascular health as blood pressure control and clean air,” wrote Professor Thomas Münzel of the University Medical Center Mainz, Germany, and his colleagues in an accompanying editorial.
The authors call on doctors to ask patients about their sleeping conditions, including “how dark the bedroom is, whether the patient works night shifts, and how much time they spend looking at screens after sunset.” They recommend using blackout curtains, warm-colored bedside lighting, and covering small standby LEDs on household electronics.
Municipal authorities also have a role to play, the authors note, because light pollution is “one of the few environmental threats that cities can control directly and inexpensively.” They cite shielded light fixtures, warm-spectrum bulbs, and dimming lights or using motion-activated streetlights as “energy-efficient and climate-friendly” ways to reduce exposure to artificial light.
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