Light from a bedside lamp or a streetlamp shining through the window does more than disturb sleep — it may also affect heart health, according to a new study. The more light people were exposed to at night, the thicker their heart walls became and the weaker their heart's pumping function.
The study, conducted by a research team at Tulane University in the United States, was published in the latest issue of the European Heart Journal and examined the link between nighttime light exposure and heart health, medical sources said on the 14th.
The team measured nighttime light exposure among 11,071 adults enrolled in the UK Biobank. Participants wore light-sensing devices on their wrists for one week, after which researchers used cardiac magnetic resonance imaging to assess the structure and function of their hearts.
Those exposed to more light at night had thicker heart muscle. The left ventricle, which pumps blood to the rest of the body, showed greater muscle mass and thicker walls. At the same time, the heart's ability to contract and squeeze out blood declined.
When the heart is under sustained strain, its muscle can thicken to cope. If that condition persists, the heart may stiffen and struggle to expand or contract fully. That can eventually leave the organ unable to circulate blood smoothly, raising the risk of heart failure and other cardiovascular disease.
In long-term follow-up, people with high nighttime light exposure faced a 29% higher risk of heart failure than those with almost no exposure. Their risk of stroke was 33% higher and their risk of myocardial infarction 24% higher.
The researchers suggested the effect may stem from disruption of the body's internal clock. Bright surroundings at night can interfere with the secretion of melatonin, a hormone that supports sleep, shortening sleep duration or making deep sleep harder to achieve. Repeated sleep loss can in turn strain the regulation of blood pressure and heart rate.
Experts advise keeping bedrooms as dark as possible during sleep. Blackout curtains can help if light from streetlamps or signs enters the room, and reducing standby lights on televisions and other electronics may also help.
The study does not prove that nighttime light directly causes heart disease. The researchers said that because an association was found between nighttime light exposure and changes in the heart, further research is needed to identify the exact cause.
