Dim nighttime light may place an unexpected strain on the heart
Sandego.net – A bedroom that seems only faintly illuminated could still matter for long-term cardiovascular health. New research suggests that exposure to light while sleeping may be linked to changes in heart-muscle structure and performance, with brighter nighttime conditions tied to a greater degree of change.
The study examined more than 11,000 adults with no diagnosed cardiovascular disease who were enrolled in the UK Biobank, a major biomedical database containing genetic and health information from 500,000 people in the United Kingdom. Its findings were published Wednesday in the European Heart Journal.
Participants wore wrist-based sensors for seven days to track overnight light exposure. About three years later, they underwent cardiovascular MRI scans that allowed researchers to assess the heart’s shape and pumping function.
More than moonlight-level brightness was linked to heart changes
Sleep specialists generally advise keeping bedrooms extremely dark, ideally at no more than 1 lux. Lux measures illumination under the International System of Units. A level of 3 lux is comparable to moonlight or the faint glow that can enter beneath a closed bedroom door.
People who slept with exposure above 3 lux showed thickening in the walls of the left ventricle, the heart chamber responsible for pumping oxygen-rich blood to the body. As those walls become thicker, the chamber’s internal space can shrink, potentially making the heart’s work less efficient.
The scans also showed a reduced ability of heart muscle to flex with each beat, an early sign that heart function may be impaired. Researchers identified additional changes in two other heart chambers. The degree of remodeling increased as nighttime light levels rose.
Common sources of unwanted bedroom light can include a phone left screen-up, a glowing digital clock, outdoor lighting entering through windows, or illumination from nearby rooms.
“Light pollution has emerged as a new risk factor for cardiovascular disease,” said senior author Dr. Lu Qi, the HCA Regents Distinguished Chair and Professor and director of the Tulane University Obesity Research Center in New Orleans.
“Our findings, together with evidence from other studies, suggest that reduction of nighttime light exposure should be considered as one of the potential strategies for preventing heart disease by clinicians and policy makers,” Qi said in a statement.
Sleep loss may explain part of the connection
Shorter sleep appeared to account for part of the association. Qi said that sleeping for less than five or six hours explained between 24% and 49% of the observed effect on the heart, describing reduced sleep duration as a direct consequence of nighttime light exposure.
The remaining share may involve other pathways. Nighttime light can affect stress and biological processes tied to cardiovascular risk, including blood pressure and heart rate. Still, the study cannot establish that light itself directly caused the heart changes.
Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, described the changes as cardiac remodeling. Freeman was not involved in the research.
“We don’t want the heart muscle to get thick. We don’t want the heart muscle to get stiff. We don’t want the heart to get too big,” Freeman said. “And all of these things seem to happen when exposed to excess light and potentially poor quality sleep.”
Important limits remain
Karl Lawrence, a lecturer at the Institute of Pharmaceutical Science at King’s College London, noted several reasons to interpret the findings carefully. A single week of light monitoring may not reflect a person’s usual exposure over months or years. A wrist sensor also does not precisely measure the amount of light reaching the eyes, meaning it may either overestimate or underestimate the relevant exposure.
“To correlate this to heart scans three years later feels like it is somewhat of a stretch,” Lawrence said in an email. “Further studies would be needed to demonstrate causality.”
Even with those limitations, the research adds to growing concern about the effects of disrupted sleep and nighttime lighting. It also points toward simple environmental changes that may support better sleep conditions.
Ways to make a bedroom darker
Heavy curtains, blackout shades, or blackout drapes can reduce outdoor light entering through windows. They should be opened in the morning, since daylight helps regulate the body’s circadian rhythm.
Indoor light can be reduced by switching off hallway lighting and removing or covering unnecessary electronic displays. When light enters through gaps around windows or beneath doors, foam strips, draft blockers, and weatherproofing materials may help close those openings.
A sleep mask can be useful when darkness cannot be achieved through the room itself. For bedtime reading, warmer bulbs in deep amber, warm white, or red tones may be preferable to brighter, cooler lighting. If a night-light is necessary, keeping it dim, close to the floor, and reddish in color can limit disruption.
For many people, these adjustments are inexpensive and practical. While more research is needed to clarify the direct effect of nighttime light on heart disease, maintaining a dark sleep environment is a straightforward step that may benefit both sleep quality and overall health.
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