Light pollution is a risk factor for many diseases: ‘We are facing a global threat’ | Health and wellness

On the pages of a book star dust (Thule Ediciones), a huge illustrated work in which the Swedish writer Hanna Arnesen reflects on the impact of man on planet Earth, contains several pages containing fragments of answers from a group of teenage schoolchildren to the question “What do you miss about life because of climate change?” ? Among these answers there are two that point to the same problem. “Darkness,” says one. “The ability to see the sky. There is light pollution where I live,” says another.

Coincidence is not a coincidence. According to the report New world atlas of artificial night sky brightnesspublished in a magazine The science In 2016, more than 80% of the world’s population and almost 100% of the population of the United States and Europe live under light-filled skies. This results in the Milky Way being hidden to six in ten Europeans and 88% of Europe’s land surface experiencing light pollution at night.

“Light pollution is a growing environmental problem. Each year, the illuminated area of ​​the world and the intensity of the artificial brightness of the night sky are growing by about 2.2%. We are faced with a threat of global reach that is growing very quickly,” reflects Alicia Pelegrina, a researcher at the Institute of Astrophysics of Andalusia (IAA). In 2021, the CSIC, through the IAA Sky Quality Authority, took part in a study which found that light pollution has increased by approximately 50% over the past 25 years.

Pelegrina, author of the essay Light pollution (The Cataract Books) argues that this threat, however, is not perceived as such by the general public because we tend to associate artificial night light with concepts such as progress, wealth, security, beauty, fun or well-being. “But let’s not kid ourselves, although light pollution cannot be touched, smelled or made, it is pollution in the strict sense of the word and poses a threat to more than just astronomical observations or the balance of ecosystems. Although knowledge about the effects of light pollution on our health is still in its infancy, it seems clear that our health is also at risk,” says the expert.

This still nascent body of research into the health effects of light pollution includes a study published in the journal iron, a journal of the American Society of Cardiology, is the first to link greater exposure to artificial bright outdoor light at night (fluorescent, incandescent and LED light sources) to an increased risk of stroke. For the study, the authors surveyed more than 28,000 adults in the Chinese city of Ningbo who were assessed for exposure to nighttime outdoor light in residential buildings using satellite imagery that mapped light pollution. The results found that people with higher levels of outdoor light exposure at night had a 43% higher risk of developing cerebrovascular disease than people with lower levels of exposure.

“Although this study has several limitations, it is new, sheds light on new risk factors for stroke and strengthens existing evidence that air pollutants influence the risk of stroke,” said Elena Lopez-Cancio, secretary of the Cerebrovascular Research Group. diseases of the Spanish Society of Neurology (SEN).

The specialist notes that there are other previous studies that have linked exposure to outdoor light at night to the risk of diabetes or hypertension, as well as its potential harmful effects on circadian rhythms and nighttime rest, and cautions that “all of these are known factors risk of stroke.” Other recent studies have also linked light pollution in recent years to significantly increased risks of breast, prostate, colorectal and thyroid cancers.

Biological clock and sleep suffer the most

According to Pelegrin, the presence of artificial light at night has two direct and immediate effects on our body: changing our biological clock and suppressing the synthesis of melatonin, the sleep hormone. Relationships with both seem clear. If our body clocks are fundamentally synchronized by alternating natural light and darkness over a 24-hour period, then the fact that a person is exposed to powerful artificial light at night will inevitably change how they function.

“When this synchronization does not occur, our circadian cycles change and our body plunges into chaos,” says the researcher from the Institute of Astrophysics of Andalusia. And this chaos, known as chronodisruption, has been linked in several epidemiological studies to an increase in both metabolic changes and cardiovascular disease, as well as the risk of cognitive decline, mood disorders and accelerated aging.

This disruption of chronology, adds Maria Angeles Bonmati, researcher at the Network Biomedical Research Center for Frailty and Healthy Aging (CIBERFES) and member of the chronobiology working group of the Spanish Sleep Society (SES), also affects the synthesis of melatonin, the hormone that makes us sleep. “Very powerful light will tell our brain that it is still daytime and that it is not time to sleep yet. And since everything in physiology is interconnected, sleeping less than our body needs leads to changes in health that can lead to serious illnesses,” explains the scientist, author of the book. Don’t let anything keep you from sleeping (Editorial criticism).

But melatonin, adds Alicia Pelegrina, has many other functions besides helping you sleep. “It is an important antioxidant agent and suppresses the growth of cancer cells, reducing the risk of tumors,” the expert emphasizes, pointing out that the antioxidant power of this hormone is necessary to stop free radicals that damage macromolecules – lipids, proteins. , carbohydrates and nucleic acids. Thus, they can change key cellular processes such as membrane functionality, enzyme production, cellular respiration, etc., contributing to the development of diseases such as atherosclerosis – one of the precipitating factors of stroke, premature aging, and high blood pressure. blood pressure and senile dementia, among others.

“Melatonin is only released at night because it requires dark conditions. Taking into account the key functions of this hormone in our body, we can say that artificial light is a very dangerous pollutant for our health,” says Pelegrina.

Correct illumination of cities

Despite significant progress in reducing traditional risk factors for cardiovascular disease, such as smoking, obesity and type 2 diabetes, “it is important to consider environmental factors such as light and air pollution in our efforts to reduce the global burden of cardiovascular disease.” especially in the most densely populated and polluted areas of the world,” Jian-Bing Wang, a researcher at Zhejiang University in China, said recently in a statement to the Journal of the American Heart Association.

Her view is echoed by Maria Angeles Bonmati, who, while admitting that it cannot be firmly established that light pollution in cities is a significant – or most significant – factor in urban poor sleep, believes that “there are many reasons” for reducing light pollution in cities . “Today, cities are overly illuminated not only due to street lighting, but also increasingly due to the installation of illuminated advertising screens and other light sources unnecessary from the point of view of city habitability,” defends the researcher, who believes that it would be advisable to plan street lighting based on real lighting needs and “raise public awareness of the possible harmful consequences of this over-lighting.”

Alicia Pelegrina also speaks in this latter sense, pointing out that the first step to reducing light pollution—and its health impacts—is to educate the public about its existence. “Light pollution comes from the misuse of artificial light, so solutions include rethinking how we use it,” adds the expert, who recommends better and more environmentally friendly lighting by avoiding emitting light directly into the sky or limiting lighting. hours in public places. Finally, it emphasizes the need to use lamps with spectral ranges visible to the human eye and to avoid white lamps, “as they are the most dangerous to our health and ecosystems, and those that are most dispersed in the atmosphere, obscuring the stars.” and making astronomical activities more difficult.

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