Light pollution and the quality of sleep


Institutional Communication Service

23 May 2022

Although light pollution may seem like a minor problem, it is actually harmful to many living things, including humans. Indeed, the unnatural presence of light affects the biological rhythms of organisms, interfering with migration, reproductive cycles, sleep and other activities. Light pollution is thought to be a major player in the decline of some species and compromises the quality of life of millions of people. We delve into the topic with Mauro Manconi, a full professor at USI Faculty of Biomedical Sciences and the University of Bern and head of service at the Neurocentro della Svizzera Italiana, responsible for the Sleep Medicine Service at the same institute. 


How much does light pollution affect sleep quality?  

The intrusion of unnecessary light into the outdoor and indoor environment is a progressively increasing phenomenon that has received little attention until a few years ago. When talking about light pollution, we mean an alteration of the natural nighttime light level operated by any artificial light source. Light sources have an important impact on the so-called "circadian cycle", that is, on the 24-hour course followed by numerous biological parameters such as blood pressure, cortisol secretion, insulin secretion, mood, cognitive performance, and especially sleep. Indeed, light is a potent inhibitor of melatonin, the neurohormone that synchronises the circadian cycle of biological functions. The groups most exposed to light pollution are night shift workers and people living in metropolitan areas. Not surprisingly, night shift workers are three times more likely than daytime workers to develop sleep disorders. Unfortunately, artificial light has an impact not only on humans but also on animals and plants and microorganisms such as bacteria, with global repercussions, even on the process of cleaning air pollution that takes place mainly at night. Within our homes, the primary source of illumination that invades the evening/night hours is produced by electronic devices such as cell phones, TVs, tablets and PCs. Those sources are enough to suppress melatonin production and cause a new and progressively increasing form of insomnia called "Techno-insomnia," which is particularly affecting young people. 


What is the situation with light pollution in Switzerland?  

Light pollution generally happens in highly populated urban areas. In Europe, the region of Lombardy and Belgium have a negative record, followed closely by London. In Switzerland, the situation is better. However, it is harder to find a place with "natural darkness" even here. The Swiss regions most affected by the phenomenon are the cantons of Zurich and Geneva, while in Ticino, it is the Sottoceneri and particularly Lugano that suffers the most light pollution. 


Do the Swiss sleep well? Is there any data on the situation in Ticino? 

It is difficult to answer these questions for two reasons. First, because there are more than 80 different sleep disorders, such as insomnia, sleep apnea, restless legs syndrome, and daytime sleepiness, to name the most frequent. Second, no studies are available on a large Swiss sample on the prevalence of insomnia, let alone in Ticino. In purely quantitative terms, in the world rankings, Japanese people sleep the least (about 6 hours/day) and the New Zealanders the most (about 8 hours/day). Switzerland ranks well with an average sleep of about 7.15 hours/day, along with Germany and the United States, higher than Italy and Spain but lower than France and the Netherlands. In Ticino, there is still little cultural and health attention to the issue of sleep, which, judging by the average consumption of sleeping pills among Ticino residents, does not seem to be in the best of health, still being among the highest in Switzerland. 


What are the effects of light pollution on bedtime, and what are the interferences during sleeping hours?  

Excessive light, especially exposure to light at the wrong times, including evenings and nights, might postpone bedtime and be associated with difficulty in falling asleep and staying asleep, resulting in sleep deprivation. The circadian cycle is altered by light. This is why light is also used as a therapy, i.e., capable of shifting the sleep phase in a different direction depending on the time at which it is administered. For therapeutic purposes, e.g., in phase delay syndrome (significant postponement of the sleep-wake cycle), by administering a white light for 20 to 30 minutes upon waking up in the morning, it is possible to stretch the sleep phase forward by about 1.5 hours after 2 to 3 weeks of therapy. Difficulty in falling asleep and increased intra-sleep awakenings, essentially insomnia and sleep deprivation in general, are only the first negative effect of abnormal light exposure. Altering the circadian cycle of numerous biological functions also increases the risk of psychological, cardiovascular and metabolic disorders in the long term. In fact, fundamental protective activities such as anti-inflammatory or antioxidant activities, which are important in the neurodegenerative and oncological spheres, occur in sleep. 


What disorders can interrupted or altered sleep cause?  

The first effect in temporal terms of prolonged sleep deprivation is psychological and cognitive. Mood decline, irritability, daytime sleepiness, problems with memory, attention, learning in children, and the ability to make context-appropriate choices are the first symptoms of chronic insomnia or generally reduced sleep in quantity or quality, even in the context of disorders other than insomnia, see, for example, sleep apnea. If sleep disturbances persist over time, the risk of hypertension and cardiovascular events, diabetes, fertility problems, gastrointestinal disorders, and possibly obesity and cancer increases.  


How much does exposure to fine particulate and nitrogen oxide that form that yellowish haze that looms over the world's metropolitan skies affect sleep quality? 

As is well known, air pollution increases the risk of numerous diseases, among them undoubtedly respiratory infections, and reduces life expectancy. We have less data on the effects of air pollution on sleep than on light pollution, but still enough to show a negative impact on sleep of particulate matter (PM), ozone and nitrogen oxide. Moreover, air pollution and sleep apnea synergistically increase health impairment. In particular, children and the elderly appear to have more vulnerable sleep when exposed to air pollution. How pollution can negatively affect sleep quality has yet to be clarified. Indeed, the nerve centre of sleep-breathing and allergy-related mechanisms could explain part of these effects. Besides, air pollution significantly increases oncological, cardiovascular, and psychiatric risks, all of which cannot be separated from sleep, which alone takes up about one-third of our lives.  


Sleeping well is essential for keeping good physical and mental health. Unfortunately, however, millions of people worldwide get little and poor sleep. What long-term consequences can occur if the situation does not change? 

On the topic of sleep duration over time, there is still disagreement in the scientific literature. Some studies indicate that the adult population has lost about 1 hour of sleep in the past 30 years, from 7.5 to 6.5 hours, while other studies show substantial stability in sleep duration in previous decades. Undoubtedly, taking an afternoon nap, which is a beneficial and physiological habit, has been lost. However, more consistent data concern sleep disorders, which tend to increase. It is estimated that about 30% of adults chronically have insomnia, with twice the prevalence in women and an average duration between 2 and 6 years. About 5% suffer from a significant form of sleep apnea, especially men; about 5% from restless legs syndrome; and about 10% of adults suffer from excessive daytime sleepiness. Sleep disorders are also common in youth, where 30% of preschool children suffer from sleep disorders, which tend to fade in school-age and recur in adolescence. Enuresis, for example, has a psychophysical impact and affects 5 per cent of 10-year-olds and 3 per cent of 16-year-olds. These numbers are unfortunately not yet supported by adequate information. Few actions are being taken regarding culture and sleep education compared to what is being done in the fight against smoking or in support of children's dental hygiene. The problem of growing consumption of stimulant drinks and cell phone use in young people is still underestimated and has a significant impact on sleep and the quality of life.