On the pages of the book star dust (Thule Ediciones), the enormous illustrated work in which the Swedish author Hannah Arnesen reflects on the impact of human beings on planet Earth, there are some pages in which fragments of the answers of a group of teenage students to the question are collected “What do you miss in life because of climate change?” Among these responses, there are two that coincide in pointing out the same problem. “Darkness,” says one. “Being able to see the sky. “Where I live there is light pollution,” says the other.
The coincidence is not a coincidence. According to report data The new world atlas of artificial night sky brightnesspublished by the magazine Science In 2016, more than 80% of the world’s population and almost 100% of the US and European population live under light-polluted skies. This causes the Milky Way to be hidden for six out of ten Europeans and 88% of Europe’s land surface experiences nights with light pollution.
“Light pollution is a growing environmental problem. Every year, the illuminated global area and the intensity of artificial brightness of the night sky grows by around 2.2%. We are facing a threat of global reach that is growing very quickly,” reflects Alicia Pelegrina, researcher at the Institute of Astrophysics of Andalusia (IAA). In 2021, the CSIC, through the IAA Sky Quality Office, participated in a study that revealed that light pollution had grown by around 50% in the last 25 years.
Pelegrina, author of the essay Light pollution (The Cataract Books), maintains that this threat, however, is not conceived as such by the population, since we tend to associate artificial night light with concepts such as progress, wealth, security, beauty, fun or well-being. “But let’s not fool ourselves, although light pollution cannot be touched, smelled or made noise, it is pollution in the strict sense of the word and poses a threat, not only to astronomical observations or to the balance of ecosystems. Although knowledge of the effects of light pollution on our health is still in its infancy, it seems clear that our health is also in danger,” says the expert.
To this still incipient body of research in the field of the health effects of light pollution, a study published in stroke, the journal of the American Society of Cardiology, which for the first time links greater exposure to artificial, bright, outdoor light at night (fluorescent, incandescent, and LED light sources) with an increased risk of stroke. For the study, the authors conducted a review of more than 28,000 adults in the Chinese city of Ningbo, who were assessed for exposure to outdoor residential nighttime light using satellite images that mapped light pollution. The result was that people with higher levels of exposure to outdoor light at night had a 43% higher risk of developing cerebrovascular disease compared to those with lower levels of exposure.
“Although it has several limitations, this study is novel, it sheds light on new factors in the risk of suffering a stroke and reinforces the existing evidence on air pollutants in the risk of suffering a stroke,” says Elena López-Cancio, Secretary of the Cerebrovascular Diseases Study Group of the Spanish Society of Neurology (SEN).
This specialist points out that there are other previous studies that have linked exposure to outdoor night light with the risk of suffering from diabetes or hypertension – as well as its potential deleterious effect on circadian rhythms and night rest – and warns that “all of them They are known risk factors for stroke.” Other recent studies have also linked light pollution in recent years with a significantly increased risk of breast, prostate, colorectal and thyroid cancer.
The biological clock and sleep, the most affected
The presence of artificial light at night has, according to Pelegrina, two direct and immediate consequences on our body: the alteration of our biological clock and the suppression of the synthesis of melatonin, the sleep hormone. The relationship with both seems clear. If our biological clock is fundamentally synchronized through the alternation that occurs between natural light and darkness in a 24-hour period, the fact that a person is exposed to powerful artificial light during the night will inevitably alter its functioning. .
“When this synchronization does not occur, our circadian cycles are altered and our body goes into chaos,” says the researcher at the Institute of Astrophysics of Andalusia. And this chaos, known as chronodisruption, has been related in several epidemiological studies to an increase in both metabolic alterations and cardiovascular diseases and the risk of cognitive decline, affective disorders and accelerated aging.
This chronodisruption, adds María Ángeles Bonmatí, researcher at the Networked Biomedical Research Center for Fragility 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 leads us to sleep. “A very powerful light will tell our brain that it is still daytime and that it is not yet time to sleep. And since in physiology everything is interrelated, sleeping less than what our body needs leads to changes in health that can lead to serious diseases,” explains the scientist, author of the book Don’t let anything keep you awake (Editorial Critica).
But melatonin, adds Alicia Pelegrina, fulfills many other functions, in addition to facilitating sleep. “It is an important antioxidant agent and inhibits the growth of cancer cells, reducing the risk of tumors appearing,” highlights the expert, who points out that the antioxidant power of this hormone is essential to stop free radicals that damage macromolecules — lipids, proteins, carbohydrates and nucleic acids. Thus, these can alter key cellular processes such as the functionality of membranes, the production of enzymes, cellular respiration, etc., favoring the development of diseases such as arteriosclerosis – one of the triggering factors of a stroke -, premature aging, high blood pressure and senile dementia, among others.
“Melatonin is only secreted at night, since 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 polluting agent for our health,” argues Pelegrina.
Correct overlighting of cities
Despite significant progress in reducing traditional cardiovascular risk factors, 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 diseases, particularly in the most densely populated and polluted areas of the world,” Jian-Bing Wang, a researcher at Zhejiang University (China), recently said in statements to the journal of the American Heart Association.
Her opinion is shared by María Ángeles Bonmatí, who, although she recognizes that it cannot be firmly stated that light pollution in cities is a relevant – or the most relevant – factor in the insufficient sleep of citizens, believes that “there are plenty of reasons.” ” to reduce light pollution levels in cities. “Today, cities are overlit, not only as a result of public lighting, but also, increasingly, due to the installation of illuminated advertising screens and other unnecessary light sources from the point of view of the habitability of a city,” defends the researcher, who considers that it would be appropriate to plan public lighting based on the real lighting needs and “raise awareness among the population about the possible harmful effects of this overlighting.”
Alicia Pelegrina also speaks out in this last sense, pointing out that the first step to reducing light pollution—and its impact on health—is to make the population aware of its existence. “Light pollution occurs from misuse of artificial light, so the solutions involve reviewing the way we use it,” adds the expert, who recommends lighting better and in a more sustainable way, avoiding the emission of light. directly to the sky or limit lighting hours in public spaces. Finally, it emphasizes using lamps with spectral ranges visible to the human eye and avoiding those that are white, “since they are the most dangerous for our health and for ecosystems, and the ones that are dispersed the most in the atmosphere, hiding the stars and making it difficult astronomical activity.
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